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AIP CONFERENCE PROCEEDINGS 1512 EDITORS A. K. Chauhan Chitra Murli S. C. Gadkari SOLID STATE PHYSICS Proceedings of the 57th DAE Solid State Physics Symposium 2012 Indian Institute of Technology, Bombay, Mumbai, India 3 – 7 December 2012 Solid State Physics (India) Vol. 57 (2012)
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Page 1: part1

AIP CONFERENCE PROCEEDINGS 1512

EDITORS

A. K. ChauhanChitra Murli

S. C. Gadkari

SOLID STATE PHYSICS

Proceedings of the 57th DAE Solid State Physics Symposium 2012

Indian Institute of Technology, Bombay, Mumbai, India 3 – 7 December 2012

Solid State Physics (India) Vol. 57 (2012)

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SOLID

STATE PH

YSICS

Proc

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57th D

AE So

lid Sta

te Physic

s Symp

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ChauhanMurli

Gadkari

1512

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ISBN 978-0-7354-1133-3ISSN 0094-243X

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SOLID STATE PHYSICSProceedings of the 57th DAE Solid State Physics Symposium 2012

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To learn more about the AIP Conference Proceedings Series, please visit http://proceedings.aip.org

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Melville, New York, 2013AIP | CONFERENCE PROCEEDINGS 1512

EDITORS

A. K. ChauhanChitra Murli

S. C. GadkariBhabha Atomic Research Centre, Mumbai, India

SOLID STATE PHYSICSProceedings of the 57th DAE Solid State Physics Symposium 2012

Indian Institute of Technology, Bombay, Mumbai, India 3 – 7 December 2012

Solid State Physics (India) Vol. 57 (2012)

All papers have been peer reviewed.

SPONSORING ORGANIZATIONSBoard of Research in Nuclear SciencesDepartment of Atomic EnergyGovernment of India

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Editors

A. K. ChauhanChitra MurliS. C. Gadkari

Bhabha Atomic Research Centre Mumbai, India

E-mail: [email protected] [email protected] [email protected]

Authorization to photocopy items for internal or personal use, beyond the free copying permitted under the 1978 U.S. Copyright Law (see statement below), is granted by the American Institute of Physics for users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that the base fee of $30.00 per copy is paid directly to CCC, 222 Rosewood Drive, Danvers, MA 01923, USA: http://www.copyright.com. For those organizations that have been granted a photocopy license by CCC, a separate system of payment has been arranged. The fee code for users of the Transactional Reporting Services is: 978-0-7354-1133-3/13/$30.00

© 2013 American Institute of Physics

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ISBN 978-0-7354-1133-3ISSN 0094-243XPrinted in the United States of America

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AIP Conference Proceedings, Volume 1512 Solid State Physics (India) Vol. 57 (2012)

Proceedings of the 57th DAE Solid State Physics Symposium

Table of Contents

Preface: Solid State Physics Symposium A. K. Chauhan, Chitra Murli, and S. C. Gadkari

1

Committees 3

INVITED TALKS

Connecting jamming and depinning transitions C. Reichhardt, Z. Nussinov, and C. J. Olson Reichhardt

7

Vibrational properties of zincblende structured ternary alloys Mala N. Rao

11

Interesting spectral evolution in Fe-based superconductors

Kalobaran Maiti, Ganesh Adhikary, Nishaina Sahadev, Deep Narayan Biswas, R. Bindu, N. Kumar, C. S. Yadav, A. Thamizhavel, S. K. Dhar, and P. L. Paulose

15

The vortex explosion transition M. N. Kunchur, M. Liang, and A. Gurevich

19

Unidirectional crystallization of charged colloids Junpei Yamanaka and Akiko Toyotama

22

Magnetic Compton scattering: A reliable probe to investigate magnetic properties B. L. Ahuja

26

Development of magnetoresistive thin film sensor for magnetic field sensing applications P. Chowdhury

30

Core/shell nano-structuring of metal oxide semiconductors and their photocatalytic studies S. Balakumar and R. Ajay Rakkesh

34

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CONTRIBUTED PAPERS

A. PHASE TRANSITIONS

Studies on melt-quenched AgInSbTe system C. Rangasami, Mahaveer K. Jain, and S. Kasiviswanathan

38

High-pressure electrical resistivity studies on FeSe2 and FeTe2 G. Parthasarathy, D. K. Sharma, Y. K. Sharma, and Usha Chandra

40

Investigation of dielectric and structural behaviour of lead free (Ba1�xCax)(Zr0.05Ti0.95)O3 ceramics Kamal Jain, Gurvinderjit Singh, G. K. Upadhyaya, and V. S. Tiwari

42

Influence of anthracene doping on the order-disorder phase transition in phenanthrene Rajul Ranjan Choudhury, R. Chitra, Lata Panicker, and V. B. Jayakrishnan

44

Study of structural phase transition and optical properties in BiFeO3-BiMnO3 thin films V. Annapu Reddy and R. Nath

46

HCP to omega martensitic phase transformation pathway in pure Zr Partha S. Ghosh, A. Arya, and G. K. Dey

48

Pressure induced phase transition in NaNbO3 S. K. Mishra, R. Mittal, S. L. Chaplot, and Thomas Hansen

50

Liquid-vapor phase diagram of metals using EAM potential Chandrani Bhattacharya

52

Role of amphiphilic molecule on liquid crystal phases Kaustabh Dan, Madhusudan Roy, and Alokmay Datta

54

Stabilisation of SrAl2O4 hexagonal phase at RT in ZnO-SrAl2O4 nanocomposite V. P. Singh, S. B. Rai, H. Mishra, and Chandana Rath

56

Effect of site selective Ti substitution on the melting point of CuTi alloys Karabi Ghosh and Manoranjan Ghosh

58

Temperature dependent structural studies of multiferroic La0.7Bi0.3CrO3 perovskites Aga Shahee and N. P. Lalla

60

Dielectric and ferroelectric studies on lead free piezoelectric KNN ceramics P. Mahesh, Ajeet Kumar, A. R. James, and D. Pamu

62

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Structural and elastic properties of ZrxNb1�xC alloy Purvee Bhardwaj, Faisal Shareef, Madhu Sarwan, V. Thakre, and Sadhna Singh

64

Structural properties of TiN and TiO at high temperature and pressure Vasudev Thakre, Sadhna Singh, Purvee Bhardwaj, and Faisal Shareef

66

Effect of high pressure on the structure of LuN Sanjay K. Singh, P. Rana, V. Nayak, and U. P. Verma

68

High pressure study of Mg1�xSrxO solid solution Mamta Chauhan and Dinesh C. Gupta

70

Structural behaviour and thermo-physical properties of PrTe: A model study M. Faisal Shareef, Madhu Singh, V. Abdul shukoor, and Sadhna Singh

72

FTIR, dielectric and impedance spectroscopic studies on Bi3.25La0.75Ti3-xZrxO12(x=0.1, 0.3, 0.5, 0.7 and 1) N. Thirumal Reddy, N. V. Prasad, G. S. Kumar, and G. Prasad

74

Structural refinement and observation of enhanced magnetic properties of La doped BiFeO3 Pittala Suresh and S. Srinath

76

High pressure phase transformation in uranium carbide: A first principle study B. D. Sahoo, K. D. Joshi, and Satish C. Gupta

78

First-principles investigations of equation of states and phase transitions in PaN under pressure P. Modak and Ashok K. Verma

80

Electronic structure, charge and orbital order and metal-insulator transition in nickelates D. Misra and A. Taraphder

82

Activation of slip systems and shape changes during deformation of single crystal copper: A molecular dynamics study S. Rawat, V. M. Chavan, M. Warrier, S. Chaturvedi, S. Sharma, and R. J. Patel

84

Ab-initio investigations of R3�c to Pm3�m transition in RAlO3 (La, Pr and Nd) perovskites under pressure Ashok K. Verma and P. Modak

86

High pressure structural investigations of copper metaborate (CuB2O4) Pallavi S. Malavi, S. Karmakar, and Surinder M. Sharma

88

Memory effect in SrRu(1-x)O3(0.01<x<0.07) Chanchal Sow, D Samal, A. K. Bera, S. M. Yusuf, and P. S. Anil Kumar

90

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Synthesis and structural characterization of highly tetragonal (1-x)Bi(Zn1/2Ti1/2)-xPbTiO3 piezoceramics Jyoti Sharma, Rishikesh Pandey, and Akhilesh Kumar Singh

92

Dielectric studies of the blue phase-III liquid crystal Manoj Marik, B. K. Chaudhuri, and D. Jana

94

Magnetic anomalies in specific heat and dielectric properties of multiferroic GdMnO3 Puneet Negi, Hemaunt Kumar, H. M. Agrawal, and R. C. Srivastava

96

Antiferromagnetic order in systems with doublet Stot = 1/2 ground states Sambuddha Sanyal, Argha Banerjee, Kedar Damle, and Anders W. Sandvik

98

High pressure behavior of BiMn2O5 K. K. Pandey, H. K. Poswal, Ravi Kumar, and Surinder M. Sharma

100

Delineating overlapping structural and magnetic phase transformations in a Fe-5.93at% Ni alloy A. Verma, Jung B. Singh, M. Sundararaman, and J. K. Chakravartty

102

Enhanced incompressibility in iron doped nano particles of indium sesquioxide under high pressure Nandini Garg, K. K. Pandey, A. K. Mishra, Anshu Singhal, and Surinder M. Sharma

104

Raman spectroscopic studies on TaVO5 Nilesh P. Salke, Rekha Rao, Jinxia Deng, and Xianran Xing

106

Structural behaviour of Mg, Al and Si doped niobium oxynitrides under high pressures

Bharat Bhooshan Sharma, H. K. Poswal, Surinder M. Sharma, J. V. Yakhmi, Y. Ohashi, and S. Kikkawa

108

B. SOFT CONDENSED MATTER INCLUDING BIOLOGICAL SYSTEMS

First principles DFT study of weak C-H…O bonds in crystalline amino acids under pressure-alanine Lavanya M. Ramaniah, C. Kamal, and S. K. Sikka

110

Dynamical motion in SDBS micelles V. K. Sharma, S. Mitra, and R. Mukhopadhyay

112

Optical and thermal properties of a lyotropic micellar nematic phase T. N. Govindaiah, H. R. Sreepad, P. M. Sathyanarayana, J. Mahdeva, and Nagappa

114

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Role of valence plasmons in transmission of photons through mica membrane in energy range 10-40eV

P. K. Yadav, Shailendra Kumar, R. K. Gupta, M. H. Modi, Pragya Tiwari, G. S. Lodha, and S. K. Deb

116

Structure of micelles in re-entrant phase of SDS/Al(NO3)3 solutions

Raisa Nadaf, Mahesh Ijjada, Janaky Narayanan, Binoj Kutty, V. K. Aswal, Jayesh R. Bellare, and P. S. Goyal

118

Surface properties of rhodamine B doped poly (vinyl) alcohol films studied using XPS and AFM J. Tripathi, S. Tripathi, J. M. Keller, K. Das, and T. Shripathi

120

Nano-Bioglass (NBG) for bone regeneration applications-Preparation and its characterization D. Durgalakshmi and S. Balakumar

122

Probing interaction of charged nanoparticles with uncharged micelles Sugam Kumar, V. K. Aswal, and J. Kohlbrecher

124

Free volume dependent fluorescence property of PMMA composite: Positron annihilation studies V. Ravindrachary, S. D. Praveena, R. F. Bhajantri, Ismayil, and Vincent Crasta

126

Free volume related electrical properties of sodium alginate/LiClO4 solid polyectrolyte S. D. Praveena, V. Ravindrachary, R. F. Bhajantri, and Ismayil

128

Study of interaction of ZnO nanoparticles with human serum albumin using fluorescence spectroscopy A. Bhogale, N. Patel, J. Mariam, P. M. Dongre, A. Miotello, and D. C. Kothari

130

Permeability studies of redox-sensitive nitroxyl radicals through bilayer lipid membranes

M. Kumara Dhas, A. Milton Franklin Benial, Kazuhiro Ichikawa, Ken-ichi Yamada, Fuminori Hyodo, A. Jawahar, and Hideo Utsumi

132

Probing the microstructure of hydrogels using fluorescence recovery after photobleaching Santripti Khandai, Ronald A. Siegel, and Sidhartha S. Jena

134

Structural refinement analysis of bulk Zn-ferrite obtained from sintering of its nanoparticles G. Thirupathi and R. Singh

136

Two dimensional mixtures at water surface Madhumita Choudhuri and Alokmay Datta

138

Bidirectional transport of motor-driven cargoes in cell: A random walk with memory Deepak Bhat and Manoj Gopalakrishnan

140

“Coffee-ring” patterns of polymer droplets Nupur Biswas and Alokmay Datta

142

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Force induced melting of DNA hairpin: A Monte Carlo study M. Suman Kalyan and K. P. N. Murthy

144

Phase transitions in methyl parben doped dipalmitoyl phosphatidylethanolamine vesicles Lata Panicker

146

A simple route to silver/polyaniline nanocomposite Javed R. Mondal and S. Bhattacharya

148

Surfactant-monomer interactions: Towards oxidative surface polymerization of transparent conducting polymers Smita Mukherjee, Anshu Kumar, Bikash K. Sikder, and Anil Kumar

150

Tuning of adsorption vs. depletion interaction in nanoparticle-polymer system Sugam Kumar, A. J. Chinchalikar, V. K. Aswal, and R. Schweins

152

Structure and interaction in liquid-liquid phase transition of silica nanoparticles in aqueous electrolyte solution A. J. Chinchalikar, V. K. Aswal, J. Kohlbrecher, and A. G. Wagh

154

Physical understanding of pore formation on supported lipid bilayer by bacterial toxins R. Bhattacharya, A. Agrawal, K. G. Ayappa, S. S. Visweswariah, and J. K. Basu

156

Preparation and introduction of CdSe quantum dots in a 5CB twisted nematic liquid crystal cell: Observation of ordered array of nanostructures Subhojyoti Sinha, Sanat Kumar Chatterjee, Jiten Ghosh, and Ajit Kumar Meikap

158

Role of electrostatic interaction on surfactant induced protein unfolding Sumit, Sugam Kumar, and V. K. Aswal

160

Computationally efficient algorithm in cluster geometry optimization Kanchan Sarkar and S. P. Bhattacharyya

162

Yielding behavior of dense microgel glasses R. G. Joshi, B. V. R. Tata, and D. Karthickeyan

164

Synthesis and characterization of metal oxide-polyaniline emeraldine salt based nanocomposite K. Siva Kumar, B. Kavitha, K. Prabakar, D. Srinivasu, Ch. Srinivas, and N. Narsimlu

166

Protonated water under hydrophobic nanoconfinement: An ab initio study M. K. Tripathy, K. R. S. Chandrakumar, and S. K. Ghosh

168

Dielectric and electric modulus study of PPy/TiO2/CNT/SLS composite with temperature D. C. Tiwari, Priyanka Atri, and Rishi Sharma

170

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Thermal properties of conformationally modified arachidic acid crystals from different solvents Debarati Bhattacharya, L. Panicker, R. Chitra, G. Abraham, and S. Basu

172

Synthesis and dielectric studies of polyorthotoluidine-polyvinyl pyrrolidone conducting polymer composites A. K. Himanshu, Rajni Bahuguna, D. K. Ray, S. K. Bandyopadyayay, and T. P. Sinha

174

C. NANO-MATERIALS

Particle distribution of nanocrystalline copper produced by exploding wire method Rashmita Das, Basanta Kumar Das, and Anurag Shyam

176

No acceptor enhanced RTFM in nitrogen doped ZnO synthesized by ammonialysis

N. Sivagami, D. Vanidha, A . Arunkumar, A. Sivagamasundari Maheswarikuppaiyandi, Nareddula Dastagiri Reddy, S. Rajagopan, and R. Kannan

178

Grain growth kinetics and its effect on instrumented indentation response to nanocrystalline Ni Arnomitra Chatterjee, Garima Sharma, and J. K. Chakravartty

180

Enhanced multiferroic properties in scandium doped Bi2Fe4O9 Dimple P. Dutta and A. K. Tyagi

182

CaMoO4:Tb@Fe3O4 hybrid nanoparticles for luminescence and hyperthermia applications A. K. Parchur, N. Kaurav, A. A. Ansari, A. I. Prasad, R. S. Ningthoujam, and S. B. Rai

184

Structural and optical studies on Mg doped CdS nanoparticles by simple co-precipitation method G. Giribabu, D. Amaranatha Reddy, G. Murali, and R. P. Vijayalakshmi

186

Crystallographic, FTIR and optical property studies on Co doped ZnS nanometer-sized crystals V. D. Mote, V. R. Huse, and B. N. Dole

188

Electronic and optical properties of free standing Au nanowires using density functional theory Anil Thakur, Arun Kumar, and P. K. Ahluwalia

190

Band gap engineering in nano structured graphane by applying elastic strain Naveen Kumar, Jyoti Dhar Sharma, Ashok Kumar, and P. K. Ahluwalia

192

Structural and electrochemical studies of LiNi0.2Co0.8VO4 cathode material for lithium batteries D. Prakash and C. Sanjeeviraja

194

Superparamagnetism in nanocrystalline CePd3: Bulk magnetization and TDPAC studies S. N. Mishra, S. K. Mohanta, S. M. Davane, K. Iyer, and E. V. Sampathkumaran

196

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Nanoindentation studies of nickel zinc ferrite embedded mesoporous silica template S. Banerjee, P. Hajra, M. R. Mada, S. Bandopadhyay, and D. Chakravorty

198

Tuning the optical properties in nanocrystalline Zn doped CdSe thin films by light soaking Kriti Sharma, Alaa S. Al-Kabbi, G. S. S. Saini, and S. K. Tripathi

200

Photoluminescence spectra of InAs quantum dots embedded in GaAs heterostructure Rahul M. Makhijani, S. Chakrabarti, and Vijay A. Singh

202

Observation of excitation wavelength dependent photoluminescence from ZnO nanoparticles embedded in mesoporous silica K. Sowri Babu, A. R. C. Reddy, Ch. Sujatha, K. V. G. Reddy, and N. K. Mishra

204

Single molecule detection using SERS study in PVP functionalized Ag nanoparticles Parul Garg and S. Dhara

206

Electrical characterization of dye sensitized nano solar cell using natural pomegranate juice as photosensitizer U. Adithi, Sara Thomas, V. Uma, and N. Pradeep

208

Surfactant doped silica aerogels dried at supercritical pressure

V. G. Parale, D. B. Mahadik, M. S. Kavale, A. Venkateswara Rao, R. S. Vhatkar, P. B. Wagh, and Satish C. Gupta

210

Photoluminescence study of ��Ga2O3 nanostructures under different oxygen pressure conditions

R. Jangir, S. Porwal, Pragya Tiwari, S. K. Rai, Puspen Mondal, Tapas Ganguli, S. M. Oak, and S. K. Deb

212

Electronic transport, ac-susceptibility, and magnetotransport studies of Pr0.6Sr0.4MnO3 manganite nanoparticles Proloy T. Das, J. Panda, A. Taraphder, and T. K. Nath

214

Structural, Raman spectroscopy and dielectric relaxation study of nanoceramics NdFeO3 Sadhan Chanda, Indrani Das, Sujoy Saha, and T. P. Sinha

216

Probing the plasmonic response of an isolated Au nanorod using cathodoluminescence Pabitra Das, Suraj Kumar Karmakar, and Tapas Kumar Chini

218

Role of Co doping on structural and morphological properties of SnO nanoparticle G. Vijayaprasath, G. Ravi, M. Arivanandhan, and Y. Hayakawa

220

Exchange bias effect in nanocrystalline Co@Co3O4 D. De, S. Majumdar, and S. Giri

222

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Determination of density of states using constant photocurrent method in nc-CdSe:Sn thin films Jagdish Kaur and S. K. Tripathi

224

Wet chemical synthesis of Ag nano wires for surface enhanced Raman spectroscopy D. Rajesh, M. Ghanashyam Krishna, and C. S. Sunandana

226

Manifestation of weak ferromagnetism and photocatalytic activity in bismuth ferrite nanoparticles M. Sakar, S. Balakumar, P. Saravanan, and S. N. Jaisankar

228

Synthesis, characterisation and counterion dependent mesoscopic modifications of ionomer nanocomposites having different dimensional silver nanostructures Sabyasachi Patra, Debasis Sen, Chhavi Agarwal, Ashok K. Pandey, S. Mazumder, and A. Goswami

230

Gold nanostars reshaping and plasmon tuning mechanism Abhitosh Kedia and P. Senthil Kumar

232

A simple novel method of developing BFO nanostructures

N. Dutta, S. K. Bandyopadhyay, P. Sen, A. K. Himanshu, P. Y. Naviraj, R. Menon, P. K. Mukhopadhyay, and P. Ray

234

Economic approach for fabricating nontoxic Cu2ZnSnS4 (CZTS) thin films for solar cell applications

Renuka Digraskar, Swapnali Dhanayat, Ketan Gattu, Sandeep Mahajan, Deepak Upadhye, Anil Ghule, and Ramphal Sharma

236

Studies on nitrogen doped ZnO nanorods synthesized through sonochemical route N. R. Panda, B. S. Acharya, and P. Nayak

238

Enhanced electrical conductivity and reduced defect emissions of ZnO:Mo nanowire array films Ajay Kushwaha and M. Aslam

240

Synthesis and structural properties of pure and co-doped (Cu, Ag) ZnO nanoparticles B. Sankara Reddy, S. Venkatramana Reddy, and N. Koteeswara Reddy

242

Structural, electrical and magnetic properties of Ni2+ substituted cobalt nanoferrite using sol-gel method

A. Paul Blessington Selvadurai, P. M. Md.Gazzali, C. Murugasen, V. Pazhanivelu, R. Murugaraj, and G. Chandrasekaran

244

Magnetic-fluorescent nanocomposite: A case study on Fe3O4/ZnS A. Roychowdhury, S. P. Pati, S. Kumar, and D. Das

246

Luminescence and electrical behavior of lead molybdate nanoparticles B. P. Singh, A. K. Parchur, S. B. Rai, and P. Singh

248

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Synthesis and photoluminescence study of flower-like hydroxyapatite nanostructure for bioprobe applications G. Suresh Kumar, E. K. Girija, and A. Thamizhavel

250

Metal-dielectric composite for dispersion free optics M. Balasubrahmaniyam, Anuradha Patra, A. R. Ganesan, and S. Kasiviswanathan

252

Effects of Cr-doping on structural and optical properties of ZnO nanoparticles Shiv Kumar, S. Chatterjee, and Anup K. Ghosh

254

Effect of size on the exciton-phonon coupling strength in ZnO nanoparticles A. Sharma, S. Dhar, and B. P. Singh

256

Size dependent absorption kinetics of sedimenting nanoparticles Manoranjan Ghosh, Karabi Ghosh, Seema Shinde, and S. C. Gadkari

258

Synthesis and characterization of nano Co0.6Fe0.4S2 Pooja Sharma and N. Razia

260

Study of B and N doped graphene by varying dopant positions Pooja Rani and V. K. Jindal

262

Effect on magnetic properties of germanium encapsulated C60 fullerene Nibras Mossa Umran and Ranjan Kumar

264

Growth of germanium nanowires by electron beam evaporation R. Rakesh Kumar, K. Narasimha Rao, and A. R. Phani

266

Growth of TiO2 nanoparticles under heat treatment J. Bahadur, D. Sen, S. Mazumder, P. U. Sastry, and B. Paul

268

Optical studies of ZnO nanoparticles and 1-D nanofibers O. Padmaraj, B. Nageswara Rao, M. Venkateswarlu, and N. Satyanarayana

270

A new type of exchange bias effect in oxidized Ni3Al compacted nanoparticles M. Umasankar, S. P. Mathew, S. N. Kaul, M. Ames, and R. Birringer

272

Synthesis of phase pure BiDyO3 and its structural characterization S. Iyyapushpam, S. T. Nishanthi, and D. Pathinettam Padiyan

274

Photoluminescence and optical absorption of LiF:Eu phosphors A. K. Sharma, Satinder Kumar, S. P. Lochab, and Ravi Kumar

276

Indium assisted growth of GaN nanowires at low temperatures Kishore K. Madapu, S. Dhara, S. Amirthapandian, and Ramanathaswamy Pandian

278

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Visible light photocatalytic degradation of 4-chlorophenol using vanadium and nitrogen co-doped TiO2 R. Jaiswal, N. Patel, D. C. Kothari, and A. Miotello

280

A comparative study of transition metal doped tubular gold cages:M@Au24 (M = Au, Cu, Ag) Sumali, Priyanka, and Keya Dharamvir

282

Co-B nanoparticles supported over FSM type mesoporous silica: An efficient nanocatalyst for hydrogen production by hydrolysis of ammonia borane S. Gupta, N. Patel, R. Fernandes, D. C. Kothari, and A. Miotello

284

The effect of annealing on the structural and magnetic properties of zinc substitutes Ni-ferrite nanocrystals Chaturbhuj Ojha, A. K. Verma, and A. K. Shrivastava

286

Evolution of silver/gold triangular nanoframes from prismatic silver/gold core/shell nanostructures and their SERS properties P. Parthiban, M. Sakar, and S. Balakumar

288

Adsorption of Eu atom at the TiO2 anatase (101) and rutile (110) surfaces Sandeep Nigam, Suman Kalyan Sahoo, Pranab Sarkar, and Chiranjib Majumder

290

DFT study of H2O adsorption on TiO2 (110) and SnO2 (110) surfaces Suman Kalyan Sahoo, Sandeep Nigam, Pranab Sarkar, and Chiranjib Majumder

292

Ammonia sensing properties of silver nanocomposite with polypyrrole N. S. Karmakar, D. C. Kothari, and N. V. Bhat

294

Synthesis, characterization and magnetic properties of nanocrystalline nickel Sourav Das, N. P. Lalla, and G. S. Okram

296

Adsorption over polyacrylonitrile based carbon monoliths Mahasweta Nandi, Arghya Dutta, Astam Kumar Patra, Asim Bhaumik, and Hiroshi Uyama

298

Interaction of nitrogen molecule with graphene Babita Rani, V. K. Jindal, and Keya Dharamvir

300

Magnetic properties of Ni(OH)2 nanostructures B. Gokul and R. Sathyamoorthy

302

The transport behavior of graphene quantum dots Hemen Kalita, V. Harikrishnan, and M. Aslam

304

In-situ study of the growth of CuO nanowires by energy dispersive X-ray diffraction

Himanshu Srivastava, Tapas Ganguli, S. K. Deb, Tushar Sant, Himanshu Poswal, and S. M. Sharma

306

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Electronic properties of anodic bonded graphene Deepika, Adrian Balan, Abhay Shukla, Escoffier Walter, and Rakesh Kumar

308

Structural, optical and antibacterial studies on Zn1�xMnxS nanomaterials M. Elango, E. M. Rajesh, R. Rajendran, and M. Thamilselvan

310

Enhanced photocatalytic performance of ZnO-reduced graphene oxide hybrid synthesized via ultrasonic probe-assisted study A. Prakash, N. K. Sahu, and D. Bahadur

312

Dielectric properties of Mn0.5Zn0.5Fe2O4 ferrite nanoparticles C. Murugesan, P. M. Md Gazzali, B. Sathyamoorthy, and G. Chandrasekaran

314

Observation of Coulomb blockade and Coulomb staircase in a lateral metal nanostructure Sourabh Barua, Rohan Poojary, and K. P. Rajeev

316

Surface controlled magnetic properties of Fe3O4 nanoparticles Jeotikanta Mohapatra, Arijit Mitra, D. Bahadur, and M. Aslam

318

Synthesis and characterization of TiO2 and Ag/TiO2 nanostructure Swati Gahlot, Amit Kumar Thakur, Vaibhav Kulshrestha, and V. K. Shahi

320

Partial inversion in nano zinc ferrite as studied using Mössbauer spectroscopy L. Herojit Singh, R. Govindaraj, G. Amarendra, and C. S. Sundar

322

Magnetic core shell nanostructures with plasmonic properties Himanshu Tyagi and M. Aslam

324

Morphology controlled synthesis of ZnO nanostructures through a mild-thermal decomposition Shripal Singh, Jeotikanta Mohapatra, A. Mitra, Ajay Kushwaha, and M. Aslam

326

Impedance and modulus spectroscopy analysis of Mn0.5Zn0.5Fe2O4 nanoparticles H. Aireddy, U. Bidayat, and A. K. Das

328

Electrical and magnetic properties of sol-gel synthesized nanocrystalline Li2Ni1�xMgxTiO4 materials Rajesh Cheruku, G. Govindaraj, and Lakshmi Vijayan

330

Structural morphological and optoelectronic study of titania and gold doped titania nanoparticles grown by sol-gel technique Yogesh A. Jadhav, Ketan P. Gattu, Anil Ghule, and Ramphal Sharma

332

Kelvin probe studies of H2S exposed CuO:ZnO nanowires random networks

Niyanta Datta, Niranjan Ramgir, Manmeet Kaur, Kailasa Ganpathi, A. K. Debnath, D. K. Aswal, and S. K. Gupta

334

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Cathodoluminescence properties of �-Ga2O3 nanowires grown using CVD technique Sudheer Kumar, C. Tessarek, S. Christiansen, and R. Singh

336

Structural and Mössbauer spectroscopic studies of heat-treated NixZn1�xFe2O4 ferrite nanoparticles Ch. Srinivas, S. S. Meena, B. V. Tirupanyam, D. L. Sastry, and S. M. Yusuf

338

Effect of dopant concentration on photoluminescence properties of Gd2O3:Eu3+ T. Selvalakshmi and A. Chandra Bose

340

Influence of cobalt doping on the structural and optical properties of ZnS nanoparticles B. Poornaprakash, D. Amaranatha Reddy, G. Murali, R. P. Vijayalakshmi, and B. K. Reddy

342

First principles study of hydrogen storage in SWCNT functionalized with MgH2 R. Lavanya, K. Iyakutti, V. J. Surya, V. Vasu, and Y. Kawazoe

344

Probing gas response of pure and Au modified ZnO nanowires network using work function measurements

Preetam K. Sharma, Niranjan S. Ramgir, N. Datta, M. Kaur, C. P. Goyal, S. Kailasaganapathi, A. K. Debnath, D. K. Aswal, and S. K. Gupta

346

A novel one-step synthesis of highly fluorescent CdSe QD’s of tunable light emission by aqueous route R. M. Hodlur and M. K. Rabinal

348

Optical studies of reduced graphene oxide thin films Kanika Anand, Nipin Kohli, Onkar Singh, Anita Hastir, and Ravi Chand Singh

350

Study of magnetization dynamics in electrodeposited magnetic nanostructures Sachin Pathak and Manish Sharma

352

Enrichment of magnetic alignment stimulated by �-radiation in core-shell type nanoparticle Mn-Zn ferrite P. P. Naik, R. B. Tangsali, B. Sonaye, and S. Sugur

354

TL kinetics study of LiF nanophosphors for high exposures of gamma-rays A. K. Sharma, Ankush Vij, Satinder Kumar, S. P. Lochab, and Ravi Kumar

356

Quantum interference effects and high magnetoresistance in textured Ni nanodots embedded in TiN matrix J. Panda and T. K. Nath

358

Fermi velocity modulation in graphene by strain engineering Harihar Behera and Gautam Mukhopadhyay

360

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Ordering of FeCo nanocrystalline phase in FeCoNbB alloy: An anomalous diffraction study P. Gupta, Tapas Ganguli, A. K. Sinha, M. N. Singh, P. Svec Jr., and S. K. Deb

362

Nanostructured zinc oxide as a prospective room temperature thermoelectric material Pawan Kumar, M. Kar, Anup V. Sanchela, C. V. Tomy, and Ajay D. Thakur

364

Electrochemical capacitance properties of Mn3O4 nanoparticles via energy efficient thermolysis Arijit Mitra, Jeotikanta Mohapatra, Balakrishna Ananthoju, and M. Aslam

366

Chunk-shaped ZnO nanoparticles for ethanol sensing R. N. Mariammal, C. Stella, and K. Ramachandran

368

MnO2 nanotube-Pt/graphene mixture as an ORR catalyst for proton exchange membrane fuel cell P. Divya and S. Ramaprabhu

370

Antibacterial efficacy of silver nanoparticles against Escherichia coli

Rani M. Pattabi, G. Arun Kumar Thilipan, Vinayachandra Bhat, K. R. Sridhar, and Manjunatha Pattabi

372

Application of multiwalled carbon nanotubes-graphene hybrid nanocomposite for nonenzymatic H2O2 biosensor Pranati Nayak, P. N. Santhosh, and S. Ramaprabhu

374

Structural phase analysis of nanocrystalline Mg:ZrO2 S. Senthilkumaran, A. Ahamed Fazil, S. Kannan, and P. Thangadurai

376

Electronic structure and electron energy loss spectra of armchair and zigzag edged buckled silicene nano-ribbons Brij Mohan, Ashok Kumar, and P. K. Ahluwalia

378

Synthesis of embedded titanium dioxide nanoparticles by oxygen ion implantation in titanium films Deepti. A. Rukade, C. A. Desai, Nilesh Kulkarni, L. C. Tribedi, and Varsha Bhattacharyya

380

Effect of calcination temperature on structural and magnetic properties of nanocrystalline magnesium ferrite powders T. P. Sumangala, C. Mahender, N. Venkataramani, and S. Prasad

382

STM observation of surface transfer doping mechanism in 3 keV nitrogen ion implanted UNCD films B. Sundaravel, Kalpataru Panda, R. Dhandapani, B. K. Panigrahi, K. G. M. Nair, and I-Nan Lin

384

Synthesis, characterization and ion conductivity study of nanocrystalline LiNaSO4 K. N. Ganesha and G. Govindaraj

386

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Synthesis and characterization of ZnS thin films deposited by CBD and UCBD techniques Sachin V. Mukhamale and N. B. Chaure

388

Effect of tautomerism on Au-6-mercaptopurine nanocluster stability Neda Rashidpour, Vikas Kashid, and Vaishali Shah

390

Al3+ doped V2O5 nanostructure: Synthesis and structural, morphological and optical characterization

A. Venkatesan, N. Krishna Chandar, M. Krishna Kumar, S. Arjunan, R. Mohan Kumar, and R. Jayavel

392

Ag+12 ion induced modifications of structural and optical properties of ZnO-PMMA nanocomposite films Sarla Sharma, Rishi Vyas, and Y. K. Vijay

394

Electronic structure investigations in conductance across porphyrin-fullerene molecular junctions Vikas Kashid, H. G. Salunke, and Vaishali Shah

396

CaSn(OH)6 cubes: Synthesis and photoluminescence studies D. K. Patel, J. Nuwad, V. Sudarsan, R. K. Vatsa, and S. K. Kulshreshtha

398

Synthesis of reduced graphene oxide and its electrochemical sensing of 4-nitrophenol K. Giribabu, R. Suresh, R. Manigandan, L. Vijayalakshmi, A. Stephen, and V. Narayanan

400

Electrochemical sensing property of Mn doped Fe3O4 nanoparticles R. Suresh, K. Giribabu, R. Manigandan, L. Vijayalakshmi, A. Stephen, and V. Narayanan

402

Microwave accelerated one-minute synthesis of luminescent ZnO quantum dots Adersh Asok, A. R. Kulkarni, and Mayuri N. Gandhi

404

Interaction of carboplatin with SWCNT (10, 10): A first principles study V. J. Surya, K. Iyakutti, H. Mizuseki, and Y. Kawazoe

406

Nanocrystalline Ni-Al ferrites for high frequency applications T. Ramesh, S. Bharadwaj, R. S. Shinde, and S. R. Murthy

408

Effect of Ga-doped ZnO seed layer thickness on the morphology and optical properties of ZnO nanorods R. Nandi, D. Singh, P. Joshi, R. S. Srinivasa, and S. S. Major

410

Impedance spectroscopy of Sn1�xCdxO2 nanoparticles Sumaira Mehraj and Alimuddin

412

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Investigations on chemosynthesized CdSe microclusters Sachin A. Pawar, S. B. Pawar, A. S. Kamble, D. S. Patil, P. N. Bhosale, and P. S. Patil

414

Enhancement of nonlinear optical absorption in copper decorated �-Fe2O3 nanoparticles Manas Ranjan Parida and C. Vijayan

416

Enhanced magnetism in ball milled Cu:TiO2 K. Bagani, M. K. Ray, B. Ghosh, N. Gayathri, M. Sardar, and S. Banerjee

418

Micromagnetic study of magnetization reversal and dipolar interactions in NiFe nano disks Janaki Sheth, D. Venkateswarlu, and P. S. Anil Kumar

420

Ion beam synthesis of Au nanoparticles embedded nano-composite glass Ranjana S. Varma, D. C. Kothari, Ravi Kumar, P. Kumar, S. S. Santra, and R. G. Thomas

422

Application of silica nanoparticles for increased silica availability in maize R. Suriyaprabha, G. Karunakaran, R. Yuvakkumar, P. Prabu, V. Rajendran, and N. Kannan

424

Thermoluminescent response of rare earth doped nanocrystalline Ba0.97Ca0.03SO4 Shaila Bahl, S. P. Lochab, Anant Pandey, and Pratik Kumar

426

Structural and ac electrical properties of LiCoPO4 synthesised by template free hydrothermal approach Lakshmi Vijayan, Rajesh Cheruku, and G. Govindaraj

428

Nano Ag-doped ZnO particles magnetic, optical and structural studies A. H. Shah, E. Manikandan, M. Basheer Ahmed, and M. Irdosh

430

Development of high strength hydroxyapatite for bone tissue regeneration using nanobioactive glass composites

Pragya Shrivastava, Sridhar Dalai, Prerna Sudera, Santosh Param Sivam, S. Vijayalakshmi, and Pratibha Sharma

432

Electron beam assisted synthesis of cadmium selenide nanomaterials M. C. Rath, A. Guleria, S. Singh, A. K. Singh, S. Adhikari, and S. K. Sarkar

434

Effect of shield gas on the size distribution of aluminum nanoparticles synthesized in thermal plasma reactor

Vijaykumar B. Varma, Chiti M. Tank, Amiya Nandi, Arti Pant, Hima Prashant, R. K. Pandey, A. K. Das, S. V. Bhoraskar, and V. L. Mathe

436

Synthesis and electrical properties of Cu-doped tin oxide nanowires Anima Johari, Manish Sharma, and M. C. Bhatnagar

438

Nanomagnetic chelators for removal of toxic metal ions Sarika Singh, K. C. Barick, and D. Bahadur

440

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Effect of nucleation and growth temperatures on the synthesis of monodisperse silver nanoparticles Chandni, O. P. Pandey, and Bhupendra Chudasama

442

175 MeV Au+13 ion irradiation induced structural and morphological modifications in zinc oxide thin films Devendra Singh, Aditya Sharma, Mayora Varshney, Shalendra Kumar, and K. D. Verma

444

Effect of particle size on the thermoluminescence properties of Ba0.97Ca0.03SO4:Cu Renuka Bokolia and P. D. Sahare

446

Preparation and characterization of Eu3+ doped In2O3 nanoparticles Kanica Anand, Digvijay Singh, Sandeep Kumar, and R. Thangaraj

448

Study of the antibacterial activity of ZnO nanoparticles Arjuman Surti, S. Radha, and S. S. Garje

450

D. EXPERIMENTAL TECHNIQUES AND DEVICES

Development of neutron tomography and phase contrast imaging technique Y. S. Kashyap, Ashish Agrawal, P. S. Sarkar, Mayank Shukla, and Amar Sinha

452

Elemental and isotopic analysis of inorganic salts by laser desorption ionization mass spectrometry T. Jayasekharan and N. K. Sahoo

454

Design and development of low cost thermoelectric power setup in the temperature range of 30 – 320 K up to a magnetic field of 8 T S. K. Giri, S. K. Hazra, and T. K. Nath

456

Study of aging of nuclear detector based on n-silicon/copper phthalocyanine heterojunction A. Ray and S. K. Gupta

458

Comparative study of ionization chamber detectors vis-à-vis a CCD detector for dispersive XAS measurement in transmission geometry A. K. Poswal, A. Agrawal, D. Bhattachryya, S. N. Jha, and N. K. Sahoo

460

Structural and optical properties of Pr doped BiFeO3 multiferroic ceramics Vikash Singh, Subhash, R. K. Dwivedi, and Manoj Kumar

462

Defect analysis of CZTS thin films using photoluminescence technique N. Poornima, V. G. Rajeshmon, C. Sudha Kartha, and K. P. Vijayakumar

464

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Ambipolar copper phthalocyanine heterojunction field effect transistors based organic inverter Sarita Yadav and Subhasis Ghosh

466

ZnO based organic-inorganic hybrid p-n junction diode Budhi Singh and Subhasis Ghosh

468

Study of nonlinear refraction of organic dye by Z-scan technique using He–Ne laser S. Medhekar, R. Kumar, S. Mukherjee, and R. K. Choubey

470

Local structure investigation of Eu doped SrSnO3 samples surrounding Sr site S. Basu, D. K. Patel, V. Sudarsan, S. K. Kulshreshtha, S. N. Jha, and D. Bhattacharyya

472

Development of Nd-YAG laser heated diamond anvil cell facility and HPHT synthesis of WGe2 N. R. Sanjay Kumar, N. V. Chandra Shekar, and P. Ch. Sahu

474

X-ray absorption near-edge structure (XANES) studies on Sb-doped Bi2UO6 at Bi and U edges

A. K. Yadav, N. L. Misra, Sangita Dhara, Rohan Phatak, A. K. Poswal, S. N. Jha, and D. Bhattacharyya

476

Tris-(8-hydroxyquinoline)aluminum thin film as ETL in efficient green phosphorescent OLEDs K. Thangaraju, Yun-Hi Kim, and Soon-Ki Kwon

478

Comparison of spectral performance of HfO2/SiO2 and TiO2/SiO2 based high reflecting mirrors

S. Maidul Haque, P. R. Sagdeo, D. Bhattacharya, D. D. Shinde, J. S. Misal, Nisha Prasad, and N. K. Sahoo

480

Neutron imaging experiments at E-12 beam-line of CIRUS Ashish Agrawal, Yogesh Kashyap, Mayank Shukla, P. S. Sarkar, and Amar Sinha

482

Doping of graphene during chemical exfoliation Pawan Kumar Srivastava, Premlata Yadav, and Subhasis Ghosh

484

On experimental realisation of a plane wave of neutrons Sohrab Abbas and Apoorva G. Wagh

486

Detection of very low concentration of water in ethanol by using NASICON probe Parul Yadav and M. C. Bhatnagar

488

Density and thermal expansion of 7010 and 7017 wrought aluminum alloys by gamma ray attenuation technique K. Gopal Kishan Rao, K. Narender, A. S. Madhusudhan Rao, and N. Gopi Krishna

490

Comparison study of LDMOS and VDMOS technologies for RF power amplifiers B. V. Ramarao, J. K. Mishra, Manjiri Pande, P. Singh, G. Kumar, and J. Mukherjee

492

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Inductively coupled plasma reactive ion etching of III-nitride semiconductors A. P. Shah, M. R. Laskar, A. A. Rahman, M. R. Gokhale, and A. Bhattacharya

494

Developing high aspect ratio comb-drive using synchrotron radiation at Indus-2 Rahul Shukla, V. K. Jain, V. P. Dhamgaye, and G. S. Lodha

496

Analysis of soft x-ray/VUV transmission characteristics of Si and Al filters Aby Joseph, Mohammed H. Modi, Amol Singh, R. K. Gupta, and G. S. Lodha

498

CSA doped polypyrrole-zinc oxide thin film sensor M. A. Chougule, D. M. Jundale, B. T. Raut, Shashwati Sen, and V. B. Patil

500

Effect of swift heavy ion irradiation on conductivity and relaxation time in PVA-PEO-EC-LiCF3SO3 blends

Prajakta Joge, D. K. Kanchan, Poonam Sharma, Manish Jayswal, Nirali Gondaliya, and D. K. Awasthi

502

Development of Fe2O3 sensor for NO2 detection S. R. Nalage, S. T. Navale, M. A. Chougule, S. G. Pawar, Shashwati Sen, and V. B. Patil

504

Effect of EC & LiCF3SO3 on conductivity and relaxation in PVA-PEO blends Prajakta Joge, D. K. Kanchan, Poonam Sharma, and Nirali Gondaliya

506

Composition and optical microstructure of good gray cast iron Nithyadevi Duraisamy and V. Veeravazhuthi

508

Development of wide band complex permeability measurement set-up Manjeet Ahlawat and R. S. Shinde

510

Study of structural disorder in Pb(Mg1/3Nb2/3)O3

Ashok Bhakar, S. M. Gupta, Tapas Ganguli, A. K. Sinha, M. N. Singh, A. Upadhyay, S. K. Deb, and P. K. Gupta

512

Dielectric and piezoelectric properties of KNN synthesized using colloidal coating approach Rajan Singh, Ajit. R. Kulkarni, and C. S. Harendranath

514

Study of electrochemical reduced graphene oxide and MnO2 heterostructure for supercapacitor application S. K. Jana, V. P. Rao, and S. Banerjee

516

Study of oxide etching for MOSFET-based MEMS-bio sensor Vikas Sharma, K. Sachdev, and V. K. Khanna

518

Dielectric constant microscopy for biological materials A. V. Valavade, D. C. Kothari, and C. Löbbe

520

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UV detector based on polycrystalline diamond films K. G. Girija and J. Nuwad

522

10B thin film based position sensitive neutron detector Shraddha S. Desai and Shylaja Devan

524

Neutron diffraction measurements of dislocation density in copper crystals deformed at high strain rate Mala N. Rao, S. Rawat, S. Sharma, V. M. Chavan, R. J. Patel, and S. L. Chaplot

526

Characterization of pulsed (plasma focus) neutron source with image plate and application to neutron radiography Sanjay Andola, Ram Niranjan, A. M. Shaikh, R. K. Rout, T. C. Kaushik, and S. C. Gupta

528

E. LIQUIDS, GLASSES AND AMORPHOUS SYSTEMS

Optical properties and Judd-Ofelt analysis of Nd3+ ions in lead-zinc-phosphate glasses R. Lakshmikantha, N. H. Ayachit, and R. V. Anavekar

530

Microstructural and electrical properties of CoCl2 doped HPMC/PVP polymer blend films H. Somashekarappa, Y. Prakash, Mahadevaiah, K. Hemalatha, and R. Somashekar

532

Photo induced effects in Bi/As2Se3 bilayer thin films Ramakanta Naik, E. M. Vinod, C. Kumar, R. Ganesan, and K. S. Sangunni

534

Photo-degradation of Lexan polycarbonate studied using positron lifetime spectroscopy K. Hareesh, A. K. Pandey, D. Meghala, C. Ranganathaiah, and Ganesh Sanjeev

536

Magnetic studies of silico-phosphate glass-ceramics containing Ag and iron oxide K Sharma, C. L. Prajapat, M. R. Singh, and G. P. Kothiyal

538

Variation of Mott parameters by chemical modification of (In50Se50)90M10 (M = Ag and Bi) thin films Shikha Gupta, Falah I. Mustafa, N. Goyal, and S. K. Tripathi

540

Kinetics of amorphous-crystallization transformation of Se85�xTe15Snx (x = 2, 4 and 6) alloys under non-isothermal conditions using Matusita's approach Balbir Singh Patial, Nagesh Thakur, and S. K. Tripathi

542

Structural and ionic conductivity behavior in hydroxypropylmethylcellulose (HPMC) polymer films complexed with sodium iodide (NaI) N. Sandhya Rani, J. Sannappa, T. Demappa, and Mahadevaiah

544

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Nonlinear optical properties of IV-V-VI chalcogenide glasses Neha Sharma, Sunanda Sharda, Vineet Sharma, and Pankaj Sharma

546

Effect of ZrO2 on solubility and thermo-physical properties of CaO�Al2O3�SiO2 glass system Madhumita Goswami, Aparna Patil, and G. P. Kothiyal

548

Er3+-doped strontium lithium bismuth borate glasses for broadband 1.5 �m emission - optical properties D. Rajesh, A. Balakrishna, and Y. C. Ratnakaram

550

Effect of Zn incorporation on the optical properties of thin films of Se85Te15 glassy alloy S. Shukla and S. Kumar

552

Structural relaxation at glass transition temperature in Li2O�B2O3 glassy ionic system Munesh Rathore and Anshuman Dalvi

554

Time evolution of photo-generated defect states in a-Se thin films Rituraj Sharma, Pritam Khan, S. Binu, and K. V. Adarsh

556

Nanosecond light induced transient absorption in a�Ge5As30Se65 thin films Pritam Khan, Rituraj Sharma, and K. V. Adarsh

558

Effect of heat treatment on green luminescence broadening of Er-doped ZnO-PbO tellurite glass ceramics Raj Kumar Ramamoorthy, Anil K. Bhatnagar, M. Mattarelli, and M. Montagna

560

Transport of polar and non-polar solvents through a carbon nanotube Manish Chopra, Rohan Phatak, and N. Choudhury

562

Synthesis and structural studies of praseodymium doped silver borate glasses G. V. Jagadeesha Gowda and B. Eraiah

564

Physical, optical and structural properties of xNa2O�(50�x)Bi2O3�10ZnO�40B2O3 glasses Sajjan Dahiya, A. S. Maan, R. Punia, R. S. Kundu, and S. Murugavel

566

Synthesis and structural studies of multi-component strontium zinc silicate glass-ceramics Babita Tiwari, M. Pandey, S. C. Gadkari, and G. P. Kothiyal

568

Quantum and classical molecular dynamics simulations of liquid methane Y. Pathania and P. K. Ahluwalia

570

Analysis of ion dynamics on Na2NbZnP3O12 glass using anomalous relaxation function N. S. Krishna Kumar, G. Govindaraj, and S. Vinoth Rathan

572

Anomalous Brillouin shift in lead-tellurite glass above glass transition S. Chakraborty, A. K. Arora, V. Sivasubramanian, and P. S. R. Krishna

574

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MN rule in a-Si:H alloys Himanshu Gupta, L. P. Purohit, F. S. Gill, and R. Kumar

576

Electrical and optical properties of ferric doped PVA-PVP-PPy composite films Ravikumar V. Patil, M. R. Ranganath, and Blaise Lobo

578

Effect of ZnO on the physical and optical properties of tellurite base glasses Sunil Dhankhar, R. S. Kundu, Rajesh Punia, Meenakshi, and Nawal Kishore

580

Magnetic and thermal properties of the ground state GdNi Pooja Rana, S. K. Singh, V. Nayak, and U. P. Verma

582

Influence of an ionic liquid on the conduction characteristics of lithium niobophosphate glass Prashant Dabas and K. Hariharan

584

Effect of alkali treatment on the physical and surface properties of Indian hemp fibers Sangappa, B. Lakshmeesha Rao, S. Asha, and R. Somashekar

586

Effect of ZnO nanoparticles on structural and mechanical properties of HPMC polymer films B. Lakshmeesha Rao, Mahadeviah, S. Asha, R. Somashekar, and Sangappa

588

Comparison of orders, structures and anomalies of water: A molecular dynamics simulation study Dibyendu Bandyopadhyay, Sadhana Mohan, Swapan K. Ghosh, and Niharendu Choudhury

590

Structural and electronic transport properties of compound forming HgPb liquid alloy using ab-initio pseudopotential Nalini Sharma, Anil Thakur, and P. K. Ahluwalia

592

Ab-initio study of liquid systems: Concentration dependence of electrical resistivity of binary liquid alloy Rb1-xCsx Anil Thakur, Nalini Sharma, Surjeet Chandel, and P. K. Ahluwalia

594

Investigation of DC electrical conductivity of chalcogenide glasses Sanjay, N. Kishore, R. S. Kundu, A. Agarwal, and S. Dhankhar

596

Structural and physical properties of vanadium doped copper bismuth borate glasses R. L. Dhiman, Virender Singh Kundu, Susheel Arora, and A. S. Maan

598

Effect of La2O3 on the electrical conductivity and thermal properties of proton conducting glasses S. R. Tiple and V. K. Deshpande

600

Luminescence, electrical and magnetic studies of Mn2+:Li2O�LiF�B2O3�CdO glasses V. Naresh and S. Buddhudu

602

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Structural, dielectric and AC conductivity properties of Co2+ doped mixed alkali zinc borate glasses B. J. Madhu, Syed Asma Banu, G. A. Harshitha, T. M. Shilpa, and B. Shruthi

604

Solvent primitive model study of structure of colloidal solution in highly charge asymmetric electrolytes Brindaban Modak, Chandra N. Patra, and Swapan K. Ghosh

606

Silver doped nanobioactive glass particles for bone implant applications M. Prabhu, K. Kavitha, G. Karunakaran, P. Manivasakan, and V. Rajendran

608

Spectroscopic studies of pure and malachite green sensitized polyvinyl carbazole films Pankaj Kumar Mishra, Jyoti Mishra, and P. K. Khare

610

Optical and microhardness measurement of lead silicate Rashmi M. Jogad, Rakesh Kumar, P. S. R. Krishna, M. S. Jogad, G. P. Kothiyal, and R. D. Mathad

612

Spectroscopy of Nd3+ in two different glassy networks: Phosphate and silicate P. Nandi, M. Goswami, M. N. Deo, V. Sudarsan, and G. P. Kothiyal

614

Acoustical and thermal conductivity studies on CuO/DEA-benzene hybrid nanofluids B. Rohini, M. Gopalakrishnan, R. Kiruba, T. Mahalingam, and A Kingson Solomon Jeevaraj

616

Mixed alkali effect in glasses containing MnO2

M. Sudhakara Reddy, Asha Rajiv, V. C. Veeranna Gowda, R. P. S. Chakradhar, and C. Narayana Reddy

618

Reitveld refinement study of PLZT ceramics Rakesh Kumar, D. V. Bavbande, R. Mishra, V. H. Bafna, D. Mohan, and G. P. Kothiyal

620

F. SURFACES, INTERFACES AND THIN FILMS

Optical properties change of Ge12.5Sb25Se62.5 thin films by laser irradiation Ramakanta Naik, E. M. Vinod, C. Kumar, and R. Ganesan

622

Fabrication of electrospun poly (methyl methacrylate) nanofiber membranes M. Sethupathy, V. Sethuraman, and P. Manisankar

624

Improved optical and electrical properties of 200 MeV Ag15+ irradiated 3 wt% 'Li' doped MoO3 thin film

M. Kovendhan, D. Paul Joseph, P. Manimuthu, S. Sambasivam, J. P. Singh, K. Asokan, C. Venkateswaran, and R. Mohan

626

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Optical properties of (SnO2/Cu-Zn ferrite) multilayers S. Saipriya and R. Singh

628

Enhanced soft magnetic properties in stress free amorphous FeTaC/Ta multilayer thin films Akhilesh Kr. Singh and A. Perumal

630

Optical constants and thickness determination of thin films using envelope method and inverse synthesis method: A comparative study S. Jena, R. B. Tokas, S. Thakur, and N. K. Sahoo

632

Growth and electrical transport study in pulsed laser deposited Sr2CoO4 thin film on (001) MgO substrate Pankaj K. Pandey, R. J. Choudhary, and D. M. Phase

634

Dispersion parameters and optical band gap in Se80.5Bi1.5Te18�ySby amorphous thin films Anup Kumar, Pawan Heera, P. B. Barman, and Raman Sharma

636

A comparative study of photoconductivity in LaTiO3/SrTiO3 and LaAlO3/SrTiO3 2-DEG heterostructures A. Rastogi, Z. Hossain, and R. C. Budhani

638

Structural and electrical properties of pure and Cu doped NiO films deposited at various oxygen partial pressures Y. Ashok Kumar Reddy, A. Mallikarjuna Reddy, A. Sivasankar Reddy, and P. Sreedhara Reddy

640

Conductive atomic force microscopy study of local electronic transport in ZnTe thin films Sachin D. Kshirsagar, M. Ghanashyam Krishna, and Surya P. Tewari

642

Preferred C-axis oriented photoluminescent ZnO thin films prepared by RF magnetron sputtering Praloy Mondal and Debajyoti Das

644

Wide band gap nanocrystalline silicon carbide thin films prepared by ICP-CVD Debjit Kar and Debajyoti Das

646

Room temperature ethanol sensing property of cubic nanostructure tungsten oxide (WO3) R. Senthilkumar, G. Ravi, C. Sanjeeviraja, M. Arivanandhan, and Y. Hayakawa

648

Annealing effect of double dip coated ZnAl2O4 thin films R. Chandramohan, V. Dhanasekaran, K. Sundaram, and T. Mahalingam

650

Mn doped nanostucture ZnO thin film for photo sensor and gas sensor application

Sandip V. Mahajan, Deepak S. Upadhye, Shahid U. Shaikh, Ravikiran B. Birajadar, Farha Y. Siddiqui, Anil V. Ghule, and Ramphal Sharma

652

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Preparation and characterization of Fe-Si-B thin films

M. Satalkar, S. N. Kane, A. Pasko, A. Apolinário, C. T. Sousa, J. Ventura, J. J. Belo, J. M. Teixeira, J. P. Araujo, F. Mazaleyrat, and E. Fleury

654

Effect of substrate on magnetic properties of La2/3Sr1/3MnO3 films

C. L. Prajapat, D. Bhattacharya, R. B. Tokas, B. K. Roul, M. R. Singh, P. K. Mishra, S. Basu, S. K. Gupta, and G. Ravikumar

656

Stability of UV exposed RR-P3BT films by spectroscopic ellipsometry Mangesh S. Diware, J. S. Byun, S. Y. Hwang, T. J. Kim, and Y. D. Kim

658

Crystal structure and magnetic properties of Zn0.9Cu0.1Oy rf-sputtered thin films M. Venkaiah, U Kumar Kiran, and R. Singh

660

Preparation and characterization of lead doped zinc oxide thin films I. Inigo Valan, V. Gokulakrishnan, A. Stephen, and K. Ramamurthi

662

Raman spectral study of electrochemically synthesized aupolyaniline composite Vijay Kumar, Yasir Ali, R. G . Sonkawade, and A. S. Dhaliwal

664

Influence of Fe layer thickness on the structure and magnetic properties of Si/Fe multilayers S. S. Das and M. Senthil Kumar

666

Synthesis and characterization of nanostructured ZnS thin film T. A. Safeera, K. J. Anju, P. J. Joffy, and E. I. Anila

668

The metastable nature of Langmuir monolayers: An attempt towards quantification Uttam Kumar Basak and Alokmay Datta

670

Structural and photoluminescence properties of ZnO/PS heterojunction Kavu Kulathuraan and Balan Natarajan

672

Fabrication of high quality nanocrystalline Cd(1�x)ZnxS thin films for optoelectronic applications Urvashi Verma, Vikas Thakur, P. Rajaram, and A. K. Shrivastava

674

Improvement of room temperature ppb level Cl2 sensing characteristics of copper phthalocyanine film Rajan Saini, Aman Mahajan, R. K. Bedi, and D. K. Aswal

676

Thermal diffusion in Ni/Al multilayer M. Swain, D. Bhattacharya, S. Singh, M. Gupta, and S. Basu

678

High resolution TOF - SIMS depth profiling of nano-film multilayers K. G. Bhushan, R. Mukundhan, and S. K. Gupta

680

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Aging and annealing effects on properties of Ag-N dual-acceptor doped ZnO thin films R. Swapna, R. Amiruddin, and M. C. Santhosh Kumar

682

In-situ TEM studies on grain growth and glassy transition in nanoscale MgF2/Cu/Si structure Puspen Mondal, Mahendra Babu, C. Mukherjee, Rajiv Kamparath, and A. K. Srivastava

684

Crystalline silicon growth in nickel/a-silicon bilayer Md Ahamad Mohiddon, K. Lakshun Naidu, G. Dalba, F. Rocca, and M. Ghanashyam Krishna

686

Dependence of optical properties of chemical bath deposited SnS2 films on deposition time G. Sreedevi and K. T. Ramakrishna Reddy

688

Hydrogen implantation-induced layer transfer of silicon using direct wafer bonding U. Dadwal, S. Chandra, P. Kumar, D. Kanjilal, and R. Singh

690

Frequency dependent FMR studies on pulsed laser ablated YIG films deposited on (111) GGG substrate B. Bhoi, N. Venkataramani, R. P. R. C. Aiyar, Shiva Prasad, Mikhail Kostylev, and R. L. Stamps

692

Spin enhancement and band gap opening of ferrimagnetic graphene on fcc-Co(111) surface upon hydrogenation Niharika Joshi, Indu Kaul, Nirmalya Ballav, and Prasenjit Ghosh

694

XPS study of 2H-TPP at Fe/Si(111) system Chhagan Lal, I. P. Jain, G. Di Santo, M. Caputo, M. Panighel, B. A. Taleatu, and A. Goldoni

696

Vapor-liquid-solid growth of GaN nanowires by reactive sputtering of GaAs P. Mohanta, P. Chaturvedi, S. S. Major, and R. S. Srinivasa

698

Construction of concentration density profile across the interface in SAN/EVA immiscible blend from positron lifetime parameters P. Ramya, D. Meghala, T. Pasang, and C. Ranganathaiah

700

Effect of ammonia plasma treatment on graphene oxide LB monolayers

Gulbagh Singh, V. Divakar Botcha, Pavan K. Narayanam, D. S. Sutar, S. S. Talwar, R. S. Srinivasa, and S. S. Major

702

Improvement in open circuit voltage of MEHPPV:FeS2 nanoparticle based organic inorganic hybrid solar cell Animesh Layek, Somnath Middya, and Partha Pratim Ray

704

Structural and optical properties of electrochemically grown highly crystalline Cu2ZnSnS4 (CZTS) thin films Balakrishna Ananthoju, Ajay Kushwaha, Farjana J. Sonia, and M. Aslam

706

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Effect of subphase pH on Langmuir-Blodgett deposition of graphene oxide monolayers on Si and SiO2/Si substrates

V. Divakar Botcha, Gulbagh Singh, Pavan K. Narayanam, D. S. Sutar, S. S. Talwar, R. S. Srinivasa, and S. S. Major

708

Fluorine doped tin oxide (FTO) thin film as transparent conductive oxide (TCO) for photovoltaic applications

Anusha Muthukumar, Germain Rey, Gael Giusti, Vincent Consonni, Estelle Appert, Hervé Roussel, Arivuoli Dakshnamoorthy, and Daniel Bellet

710

Role of oxygen annealing on charge order and insulator metal transition in Pr0.58Ca0.42MnO3 thin films Vasudha Agarwal and H. K. Singh

712

Manifestation of surface and interface properties of Ag overlayer on Si (111) A. H. M. Abdul Wasey, R. Batabyal, B. N. Dev, and G. P. Das

714

FTIR study of thin film of uracil on silanised glass substrate using attenuated total reflection (ATR) Naveen Kumar, Susy Thomas, and R. J. Kshirsagar

716

Effect of oxide insertion layer on resistance switching properties of copper phthalocyanine Nikhil G. Joshi, Nirav C. Pandya, and U. S. Joshi

718

Study of GaFeO3 thin films prepared by PLD

Kavita Sharma, V. Raghavendra Reddy, Ajay Gupta, R. J. Choudhary, D. M. Phase, A. Banerjee, and V. Ganesan

720

Impact of quenched disorder on magnetotransport properties in Nd0.55-xSmxSr0.45MnO3 thin films Manoj K. Srivastava, Amarjeet Kaur, and H. K. Singh

722

Fourier transform infrared study of pulsed laser deposited Fe3O4 thin films grown on different substrates Ridhi Master, D. M. Phase, R. J. Choudhary, U. P. Deshpande, and T. Shripathi

724

Preparation and characterization of Gd2O3 thin films by RF magnetron sputtering Manjunatha Pattabi and G. Arun Kumar Thilipan

726

SERS study of Pd-CTAB interactions in monolayer film A. Das, K. Priya Madhuri, Sonu Mewada, S. Dhara, and A. K. Tyagi

728

Effect of annealing on structure and magneto-transport properties of Fe/Au multilayer Surendra Singh, Saibal Basu, C. L. Prajapat, and M. Gupta

730

Emission properties of Ag@SiO2/ZnO nanorods' heterostructure Moumita Mahanti and Durga Basak

732

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Exchange coupled Co-ferrite/Zn-ferrite bilayer

Subasa C. Sahoo, Baidyanath Sahu, Murtaza Bohra, N. Venkataramani, Shiva Prasad, and R. Krishnan

734

Crystalline SrBi4Ti4O15 thin films on amorphous substrates sputtered by rf sputtering A. Rambabu and K. C. James Raju

736

Anomalous X-ray scattering study of quantum dots embedded in MBE grown silicon/germanium multilayers Manjula Sharma, Milan K. Sanyal, and Mrinmay K. Mukhopadhyay

738

Early stage fractal growth in thin films below the percolation limit R. Batabyal, J. C. Mahato, Debolina Das, and B. N. Dev

740

Impact of fringing field on the C-V characterization of HfO2 high-� dielectric MOS (p) capacitors fabricated through atomic layer deposition Savita Maurya, B. R. Singh, and M. Radhakrishna

742

Structural characterization of polyelectrolyte thin film prepared under applied electric potential Tanusree Samanta and M. Mukherjee

744

Growth and morphology of rubrene thin films on hydrophilic and hydrophobic substrates S. Sinha, C.-H. Wang, A. K. M. Maidul Islam, Y.-W. Yang, and M. Mukherjee

746

Simultaneous growth of sub-nanometer deep vacancy island and epitaxial silicide islands on Si (111) J. C. Mahato, Debolina Das, R. Batabyal, and B. N. Dev

748

The electrochemical performance of SnO2 film incorporated with RuO2 S. N. Pusawale, P. R. Deshmukh, and C. D. Lokhande

750

Effect of post-deposition treatment on energy conversion efficiency of nanostructured CdS/Cu2S thin films Vidya S. Taur, Rajesh A. Joshi, and Ramphal Sharma

752

Study of percolation behavior in semiconducting La0.95MnO3/polyvinylidene fluoride nanocomposites K. Devi Chandrasekhar, P. M. Manjunatha, N. Vijay Prakash Chaudhary, and A. Venimadhav

754

Oxygen partial pressure influenced structural and optical properties of DC magnetron sputtered ZrO2 films P. Kondaiah, V. Madhavi, and S. Uthanna

756

Electrochemical properties of magnetron sputtered WO3 thin films V. Madhavi, P. Kondaiah, O. M. Hussain, and S. Uthanna

758

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A novel high transmittance red color filter: ZnS and Ag multilayer Garima Kedawat, Vipin Kumar Jain, Subodh Srivastava, and Y. K. Vijay

760

Growth temperature effect on a-Si:H thin films studied by constant photocurrent method N. A. Wadibhasme and R. O. Dusane

762

Influence of RF power on magnetron sputtered AZO films Mohit Agarwal, Pankaj Modi, and R. O. Dusane

764

Optimization of manganites thin film for electric field and strain control Himanshu Sharma, Sourabh Jain, D. Dixit, C. V. Tomy, and A. Tulapurkar

766

Characterization of Ni/Zr system by x-ray reflectivity measurements Debarati Bhattacharya, Pooja Moundekar, and Saibal Basu

768

Electron accumulation/depletion at F16CoPc/Znq3 heterojunction: Kelvin probe and charge transport study

Ashwini Kumar, R. Prasad, Arvind Kumar, Soumen Samanta, Ajay Singh, A. K. Debnath, D. K. Aswal, and S. K. Gupta

770

Poly(2,7-carbazole) derivative based air stable and flexible organic field effect transistor

Purushottam Jha, P. Veerender, S. P. Koiry, Vibha Saxena, A. Gusain, A. K. Chauhan, D. K. Aswal, and S. K. Gupta

772

Improved efficiency of organic dye sensitized solar cells through acid treatment

Avani Jain, P. Veerender, Vibha Saxena, Abhay Gusain, P. Jha, S. P. Koiry, A. K. Chauhan, D. K. Aswal, and S. K. Gupta

774

Investigation on the effects of thermal annealing on PCDTBT:PCBM bulk-heterojunction polymer solar cells

Abhay Gusain, Vibha Saxena, P. Veerender, P. Jha, S. P. Koiry, A. K. Chauhan, D. K. Aswal, and S. K. Gupta

776

Effect of Co-sensitization and acid treatment on TiO2 photoanodes in dye-sensitized solar cells

P. Veerender, Vibha Saxena, Abhay Gusain, P. Jha, S. P. Koiry, A. K. Chauhan, D. K. Aswal, and S. K. Gupta

778

H2S sensing properties of RF sputtered SnO2 films

Kailasa Ganpathi, Manmeet Kaur, Niranjan Ramgir, Niyanta Datta, Shovit Bhattacharya, A. K. Debnath, D. K. Aswal, and S. K. Gupta

780

Enhanced H2S response of Au modified Fe2O3 thin films

Vishal Balouria, A. Singh, Niranjan S. Ramgir, A. K. Debnath, Aman Mahajan, R. K. Bedi, D. K. Aswal, and S. K. Gupta

782

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Effect of substrate temperature on optical and morphological properties of ZrO2-MgO composite films R. B. Tokas, S. Jena, N. M. Kamble, S. Thakur, and N. K. Sahoo

784

Effect of post deposition annealing on the performance of copper phthalocyanine based organic thin film transistor N. Padma, Shilpa N. Sawant, Shaswati Sen, and S. K. Gupta

786

High dielectric permittivity in BaFe12O19/polyvinylidene fluoride composites K. Devi Chandrsekhar, S. Karthikeyan, A. K. Das, and A. Venimadhav

788

Activation studies of NEG coatings by surface techniques R. K. Sharma, Jagannath, K. G. Bhushan, S. C. Gadkari, R. Mukund, and S. K. Gupta

790

TSDC and x-ray diffraction analysis of pure and malachite green sensitized polyvinyl carbazole films Pankaj Kumar Mishra, Jyoti Mishra, Rachana Kathal, Hariom Pandey, and P. K. Khare

792

Studies of thin films of Ti- Zr -V as non-evaporable getter films prepared by RF sputtering

Nidhi Gupta, Jagannath, R. K. Sharma, S. C. Gadkari, K. P. Muthe, R. Mukundhan, and S. K. Gupta

794

G. ELECTRONIC STRUCTURE AND PHONONS

Effect of Si doping on ductility of RuAl intermetallics: A first principle study Bushra Fatima, Nikita Acharya, Sunil Singh Chouhan, and Sankar P. Sanyal

796

Low temperature Raman spectra of rhombohedral La0.925Na0.075MnO3 Neha Dodiya, A. Yogi, and Dinesh Varshney

798

Temperature dependent Raman study of Eu0.75Y0.25MnO3 Dileep K. Mishra and V. G. Sathe

800

First-principles study of structure and electronic properties of phenyl imidazole H. R. Sreepad, M. Ramegowda, Khaleel Ahmed, H. M. Dayananda, and Manohara

802

Influence of Co doping on structural and electrical properties of La0.5Ce0.5Mn1�xCoxO3 manganites Irfan Mansuri, M. W. Shaikh, Y. K. Kuo, and Dinesh Varshney

804

A generalised algebraic approach to states having same energy but different potential strengths Subha Gaurab Roy and Ramendu Bhattacharjee

806

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xxxv

Raman scattering in 2H-MoS2 single crystal M. P. Deshpande, Sandip V. Bhatt, Vasant Sathe, Bindiya H. Soni, Nitya Garg, and S. H. Chaki

808

Bipolaron by inter-site electron-phonon interaction N. S. Mondal, S. Nath, S. Bose, and M. Paul

810

Colossal thermal expansion behavior of Ag3M(CN)6 (M=Co,Fe) R. Mittal, M. Zbiri, H. Schober, S. N. Achary, A. K. Tyagi, and S. L. Chaplot

812

Vibrational modes and electronic structure of Sr2GdTaO6 Binita Ghosh, Sadhan Chanda, Anup Pradhan Sakhya, and T. P. Sinha

814

Evidence of unusual spin polarization of the surface states of W(110) surface

Deep Narayan Biswas, Partha Sarathi Mandal, Shyama R. Varier, Nishaina Sahadev, and Kalobaran Maiti

816

Study of the surface electronic structure of Si(111) surface using spin and angle resolved photoemission spectroscopy

Shyama R. Varier, Partha Sarathi Mandal, Nishaina Sahadev, Deep Narayan Biswas, and Kalobaran Maiti

818

Occurrence of diverse bonding characteristics in CaNi2As2 and CaPd2As2: A theoretical study D. S. Jayalakshmi, M. Sundareswari, and M. Manjula

820

First principle study on structural, mechanical and electronic properties of REAg (RE-Y, La, Pr and Er) intermetallic compounds A. Sahu, Chandrabhan Makode, J. Pataiya, and Sankar P. Sanyal

822

Comparative study of NaTiO2 and NaNiO2 using first principle calculations Monika Dhariwal, T. Maitra, and Ishwar Singh

824

Instability in coupled electron quantum layers with finite width L. K. Saini and Mukesh G. Nayak

826

Evidence of bulk nature of the Kondo effect and different surface potentials in CeB6

Nishaina Sahadev, Deep Narayan Biswas, Sangeeta Thakur, Khadiza Ali, Geetha Balakrishnan, and Kalobaran Maiti

828

Structural properties of solid nitromethane: A density functional study S. Appalakondaiah and G. Vaitheeswaran

830

Electronic structure and magnetic ordering of MgV2O4 Ramandeep Kaur, Tulika Maitra, and Tashi Nautiyal

832

The momentum distribution function of a Luttinger liquid P. J. Monisha, Soma Mukhopadhyay, and Ashok Chatterjee

834

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First-principles study of fluorination of L-Alanine H. R. Sreepad, H. R. Ravi, Khaleel Ahmed, H. M. Dayananda, K. Umakanth, and B. M. Manohara

836

Study of thermally induced spin state transition in NdCoO3 single crystal J. Janaki, R. Nithya, S. Ganesamoorthy, T. N. Sairam, T. R. Ravindran, K. Vinod, and A. Bharathi

838

Density functional study on CeMo2Si2C U. B. Paramanik, Anupam, C. Geibel, Z. Hossain, and R. Prasad

840

Electronic structure of Co2MnSn Heusler alloy

Madhusmita Baral, Soma Banik, Tapas Ganguli, Aparna Chakrabarti, A. Thamizhavel, D. M. Phase, A. K. Sinha, and S. K. Deb

842

Optical absorption in B13 cluster: A time-dependent density functional approach Ravindra Shinde and Meenakshi Tayade

844

Ab initio calculations of yttrium chromite Vidhya G. Nair, C. Ganeshraj, P. N. Santhosh, and V. Subramanian

846

Large scale configuration interaction calculations of linear optical absorption of octacene and nonacene Himanshu Chakraborty and Alok Shukla

848

Designing a new class of III-IV-V semiconductor nanosheets A. Bhattacharya, S. Chakrabarty, and G. P. Das

850

Ab-initio study of Fe doped molybedenum dichalcogenides Chamma Tiwari, Ramesh Sharma, and Yamini Sharma

852

High pressure infrared reflectivity measurements on copper doped Ru1212 Himal Bhatt, S. Karmakar, M. N. Deo, M. R. Gonal, N. Patel, and Surinder M. Sharma

854

H. SINGLE CRYSTALS

Detached phenomenon: Its influence on the crystals quality of InSb:Te grown by the VDS technique D. B. Gadkari

856

Molecular dynamics simulation of He diffusion in FeCr alloy A. Abhishek, M. Warrier, and E. Rajendra Kumar

858

The oxalic acid: 2-chloroacetamide crystallization: A new revelation R. Chitra, R. R. Choudhury, Frederic Capet, and Pascal Roussel

860

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Growth of silver doped Li2B4O7 single crystals for dosimetric application G. D. Patra, S. G. Singh, A. K. Singh, D. G. Desai, B. Tiwari, S. Sen, and S. C. Gadkari

862

Scintillation yield uniformity studies on single crystals of Tl doped CsI D. G. Desai, S. G. Singh, A. K. Singh, Shashwati Sen, Seema Shinde, and S. C. Gadkari

864

Optical and dielectric properties of L-methionine L-methioninium hydrogen maleate single crystal P. Vasudevan, S. Sankar, and S. Gokulraj

866

Development of high quality, direction controlled ADP single crystals and the effect of impurities on their growth P. Rajesh and P. Ramasamy

868

Effect of cation size at Gd and Al site on Ce energy levels in Gd3(GaAl)5O12 sintered pellets Mohit Tyagi, Fang Meng, Kaitlyn Darby, Merry Koschan, and C. L. Melcher

870

Transport, electrical and microtopography studies of W3Se4 single crystals D. N. Bhavsar and A. R. Jani

872

Unidirectional growth of potassium hydrogen malate single crystals and its characterizations on optical, mechanical, dielectric, laser damage threshold studies K. Boopathi, P. Rajesh, and P. Ramasamy

874

Effect of temperature gradient on detachment of the crystals grown by vertical directional solidification D. S. Maske, M. Joshi, R. Choudhary, and D. B. Gadkari

876

Effect of Ce concentration on optical properties of Li6Gd(BO3)3 single crystals A. K. Singh, S. G. Singh, D. G. Desai, S. Sen, and S. C. Gadkari

878

Single crystal growth of 4-chloro-3-nitrobenzophenone using nanoresolution translation by Bridgman technique and its characterization K. Aravinth, G. Babu Anandha, and P. Ramasamy

880

Study of surface microstructure and optical properties of as-grown Mo0.6W0.4Se2 single crystals Sunil H. Chaki, M. P. Deshpande, Jiten P. Tailor, M. D. Chaudhary, and K. S. Mahato

882

Synthesis and X-ray structural studies of novel metal-organic complex: Diiodobis(2-aminopyridine)cadmium(II) single crystal G. Venkatesan, G. Babu Anandha, and P. Ramasamy

884

Thermoluminescent dosimetric characteristics of irradiated ternary alkali halides doped with lanthanum G. Maruthi and R. Chandramani

886

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Effect of stirring on the growth rate anisotropy of the metastable �-glycine single crystals K. Renuka Devi and K. Srinivasan

888

Influence of PT composition on the properties of PZN-PT single crystals B. Srimathy, R. Jayavel, and J. Kumar

890

Growth of Ce added NBT-BT single crystal by flux method and its characterization S. Shanmuga Sundari and R. Dhanasekaran

892

Influence of solvents on the habit modification of alpha lactose monohydrate single crystals P. Parimaladevi and K. Srinivasan

894

Nucleation control and growth of metastable �-L-glutamic acid single crystals in the presence of L-tyrosine P. Dhanasekaran and K. Srinivasan

896

Growth and characterization of N,N-diethyl anilinium picrate (NNDEAP) single crystals R. Subramaniyan, G. Babu Anandha, and P. Ramasamy

898

Study of the flow properties using simulation modeling for the melt growth by Bridgman-Stockbarger method M. Srinivasan and P. Ramasamy

900

Indentation size effect on some glycine based nonlinear optical crystals N. Gopi Krishna, Ch. Sateesh Chandra, D. Nagaraju, and P. V. Shekar

902

Optical properties of Eu2+ doped antipervoskite fluoride single crystals D. Joseph Daniel, R. Nithya, P. Ramasamy, and U. Madhusoodanan

904

Growth and characterization of L-serine formate nonlinear optical single crystal P. Krishnan, K. Gayathri, and G. Anbalagan

906

Linear optical and SHG characterization of new chalcone crystals S. Raghavendra, A. Jayarama, T. Chandra Shekhara Shetty, and S. M. Dharmaprakash

908

Growth and characterization of a nonlinear optical crystal: Bisglycine hydrogen chloride Ch. Sateesh Chandra, N. Gopi Krishna, P. V. Raja Shekar, and D. Nagaraju

910

The negative thermal expansion coefficient in lithium niobate single crystals J. C. Vyas and S. G. Singh

912

Structural, morphological and electrical studies of lithium ion irradiated sodium potassium niobate single crystal grown by flux method R. Saravanan, D. Rajesh, S. V. Rajasekaran, R. Perumal, M. Chitra, and R. Jayavel

914

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Impact of firing on the optically stimulated luminescence of geological quartz D. K. Koul and G. S. Polymeris

916

I. TRANSPORT PROPERTIES

Diffusion of water in bentonite clay: Neutron scattering study

V. K. Sharma, S. A. Prabhudesai, R. Raut Dessai, J. A. Erwin Desa, S. Mitra, and R. Mukhopadhyay

918

Millisecond transient current investigations in vectra B950 polymer liquid crystal J. K. Quamara, S. K. Mahna, and Sanjeev Garg

920

Synthesis, electrical and thermal properties of Bi4V2�xZrxO11 (x=0.0 & 0.02) ceramics S. Sahu, S. K. Barbar, S. Jangid, and M. Roy

922

Effect of ionic-size change of the rare earth ion on the electrical properties of the hole doped double perovskite Gd0.95Sr0.05BaCo2O5.5 J. Janaki, V. Rajaji, T. Geetha Kumary, S. Kalavathi, and A. Bharathi

924

Anisotropic behavior of DC resistivity in Sr3NiPtO6 and Sr3CuPtO6 single crystals S. Chattopadhyay and S. Majumdar

926

Structure-property correlations in monovalent mixed oxide La1�xKxMnO3(0.0 x 0.3 manganites

Davit Dhruv, R. K. Trivedi, Bhumika Nimavat, Sanjay Kansara, D. D. Pandya, M. J. Keshvani, P. S. Solanki, Bharat Kataria, D. G. Kuberkar, and N. A. Shah

928

Structural and transport properties of NdCrO3 nanoceramics Sujoy Saha, Anup Pradhan Sakhya, Sayantani Das, and T. P. Sinha

930

Polaronic glassiness in Pr0.5Ca0.5MnO3� A. Karmakar, S. Majumdar, and S. Giri

932

Dielectric relaxation in multiferroic BiFeO3 K. Dey, S. Majumdar, and S. Giri

934

Effect of porosity on impedance of CaF2 ceramic Shashwati Sen, Garima Mittal, S. K. Deshpande, and S. C. Gadkari

936

Effect of HCl doping in polyaniline: Transport and optical studies J. Sannigrahi and S. Majumdar

938

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Monte Carlo simulation of charge transport in disordered organic thin films: Applicability of Meyer-Neldel rule for extracting energetic disorder S. Raj Mohan, Manoranjan P. Singh, M. P. Joshi, and L. M. Kukreja

940

Effect of Y doping on magnetic and transport properties of La0.7Sr0.3CoO3

G. D. Dwivedi, K. K. Shukla, P. Shahi, O. K. Jha, A. K. Ghosh, A. K. Nigam, and Sandip Chatterjee

942

Evanescent mode transport and its application to nano-electronics Sreemoyee Mukherjee and Prosenjit Singha Deo

944

Structural and dielectric properties of Y1/2Er1/2FeO3 Indrani Das, Sadhan Chanda, Alo Dutta, Sourish Banerjee, and T. P. Sinha

946

Electrical properties of strontium doped yttrium manganite oxide Rajesh K. Thakur, Rasna Thakur, N. Kaurav, G. S. Okram, and N. K. Gaur

948

Lattice thermal conductivity of bilayer graphene M. D. Kamatagi, S. M. Galagali, N. S. Sankeshwar, and B. G. Mulimani

950

Molecular dynamics dependence of overhauser-enhanced magnetic resonance imaging (OMRI): An ESR study

V. Meenakumari, A. Milton Franklin Benial, Kazuhiro Ichikawa, Ken-ichi Yamada, A. Jawahar, and Hideo Utsumi

952

High ionic conductivity and desirable stability properties of PNC for renewable energy applications A. L. Sharma and Awalendra K. Thakur

954

Structural and transport properties of Dy substituted YBaCo4O7 Bharat Singh, Naresh Kumar, S. Rayaprol, and N. K. Gaur

956

Pore topology and diffusion of acetylene in CuBTC metal organic framework S. A. Prabhudesai, V. K. Sharma, S. Mitra, and R. Mukhopadhyay

958

Energy and momentum loss rates of hot electrons in a supported bilayer graphene K. S. Bhargavi and S. S. Kubakaddi

960

Absolutely continuous spectrum and ballistic transport in a one-dimensional quasiperiodic system Biplab Pal and Arunava Chakrabarti

962

High pressure studies on topological insulator Bi2Se3 T. R. Devidas, Awadhesh Mani, and A. Bharathi

964

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Synthesis and electrical transport properties of SnS nanoparticles S. H. Chaki, M. P. Deshpande, M. D. Chaudhary, J. P. Tailor, and K. S. Mahato

966

Structural and dielectric properties of LaFe1�xZnxO3(0x0.3) Irshad Bhat, Shahid Husain, and Wasi Khan

968

Observation of current-induced voltage jump at low temperature in VO2 nanowires

Shubhankar Das, A. Rastogi, P. C. Joshi, Mandeep Kaur, S. C. Husale, T. D. Senguttuvan, Z. Hossain, W. Prellier, and R. C. Budhani

970

Competing Kondo and e-e interaction in Ce2.1Nd0.9Al

Durgesh Singh, S. Shanmukharao Samatham, D. Venkateshwarlu, Mohan Gangrade, and V. Ganesan

972

Study of dielectric relaxation at room temperature of the composite (100-x) LCMO/(x) BTO Momin Hossain Khan, Sudipta Pal, and Esa Bose

974

Electrical properties of Ba doped LSGM for electrolyte material of solid oxide fuel cells Raghvendra, Prabhakar Singh, and Rajesh Kumar Singh

976

Structural and transport properties of two new Heusler type Ru2VAl and Ru2VGa compounds Sanchayita Mondal, Chandan Mazumdar, and R. Ranganathan

978

Sb concentration dependent power factor of n-type thermoelectric material Bi1�xSbx alloy K. Malik, Diptasikha Das, A. K. Deb, S. Bandyopadhyay, and Aritra Banerjee

980

Single molecule conductance: Role of electrode morphology at the nanoscale Divakar Ravi, C. P. Karthika, and Arijit Sen

982

Influence of particle shape on viscosity of nanofluids Gaganpreet and Sunita Srivastava

984

Contrasting effects of compressive and tensile strain and doping-induced opening of charge-transfer gap in NdNi0.90Mn0.10O3 thin films Mahesh Chandra, Amit Khare, Fozia Aziz, Rakesh Rana, D. S. Rana, and K. R. Mavani

986

Fabrication and characterization of indium gallium zinc oxide (IGZO) thin film transistors with (La0.5Y0.5)2O3 gate insulator Bhaumik V. Mistry, Jaydeep Mistry, U. N. Trivedi, V. G. Joshi, and U. S. Joshi

988

Structural and dielectric properties of Zn1�xMgxO Parmod Kumar, Yogesh Kumar, Hitendra K. Malik, and K. Asokan

990

Dependency of dielectric constant on the cation distribution for magnetite nanoparticles Geeta Rana, Deepika Kandpal, and Umesh C. Johri

992

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xlii

Electrical and magnetic property of Al62Cu25.5Fe12.5 icosahedral quasicrystal: Spin-orbit scattering

M. K. Ray, K. Bagani, B. Ghosh, M. Sardar, S. Banerjee, V. C. Srivastava, and N. K. Mukhopadhyay

994

Effect of TiO2 ceramic filler on PEG-based composite polymer electrolytes for magnesium batteries Anji Reddy Polu, Ranveer Kumar, K. Vijaya Kumar, and N. Krishna Jyothi

996

Nonlinear dielectric response of BaBi4Ti4O15 ceramics Sunil Kumar, D. A. Ochoa, J. E. Garcia, and K. B. R. Varma

998

Enhanced figure of merit in (AgCrSe2)0.75(CuCrSe2)0.25 S. Bhattacharya, R. Bhatt, R. Basu, A. Singh, D. K. Aswal, and S. K. Gupta

1000

Dramatic thermal conductivity reduction in PbSe0.5Te0.5 Ranita Basu, S. Bhattacharya, Ranu Bhatt, Ajay Singh, D. K. Aswal, and S. K. Gupta

1002

Influence of Cu intercalation on thermal transport properties of titanium diselenide R. Bhatt, S. Bhattacharya, R. Basu, A. Singh, D. K. Aswal, and S. K. Gupta

1004

Flux induced fano peak splitting in asymmetric coupled quantum dot system Bharat Bhushan Brogi, Shyam Chand, and P. K. Ahluwalia

1006

Anomalous dielectric and AC conductivity behavior of the nanocrystalline Ni-Cu ferrite synthesized via combustion method B. J. Madhu, B. N. Rashmi, Arshiya Banu, G. A. Seema, B. Shruthi, and H. S. Jayanna

1008

Structure and properties of RELiGe2 (RE = La-Nd, Sm-Gd, Yb) compounds Abishek K. Iyer, Udumula Subbarao, and Sebastian C. Peter

1010

J. SEMICONDUCTOR PHYSICS

Effects of magnetic field and the built-in internal fields on the absorption coefficients in a strained wurtzite GaN/AlGaN quantum dot N. S. Minimala and A. John Peter

1012

Strain induced optical gain in a ZnxCd1�xTe/ZnTe quantum dot nanostructure R. Sangeetha and A. John Peter

1014

Mechanical stiffening of transition metal carbides: XC X = Ti, Zr, Nb, Hf, Ta) Dinesh Varshney, S. Shriya, and Namita Singh

1016

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Effects of gallium alloy content and the geometrical confinement on effective exciton g-factor in a III-V semiconductor quantum dot N. R. Senthilkumar and A. John Peter

1018

Dielectric effect of changes of refractive index in a Mg based II-VI semiconductor nanostructure J. Abraham Hudson Mark and A. John Peter

1020

Enhanced thermoelectric properties of Pb0.90Sn0.10Te by Yb P. K. Rawat, B. Paul, and P. Banerji

1022

Studies on ZnO nanorods/CuInS2 coaxial n-p heterojunction arrays Shrabani Panigrahi and Durga Basak

1024

Synthesis of nanocrystalline thin films of gold on the surface of GaSb by swift heavy ion Vidya Jadhav, S. K. Dubey, A. D. Yadav, and A. Singh

1026

Reliability studies on Si PIN photodiodes under Co-60 gamma radiation Y. P. Prabhakara Rao, K. C. Praveen, Y. Rejeena Rani, and A. P. Gnana Prakash

1028

A comparison of 75 MeV boron and 50 MeV lithium ion irradiation effects on 200 GHz SiGe HBTs K. C. Praveen, N. Pushpa, H. B. Shiva, J. D. Cressler, Ambuj Tripathi, and A. P. Gnana Prakash

1030

Dielectric response of polyethersulphone (PES) polymer irradiated with 145 MeV Ne6+ ions S. Asad Ali, Rajesh Kumar, Wasi Khan, A. H. Naqvi, and R. Prasad

1032

Annealing behavior of cadmium ion implanted GaSb S. D. Pandey and S. K. Dubey

1034

Structural, optical and electrical studies on CdO thin films using spray pyrolysis technique K. Sankarasubramanian, R. Solaichamy, K. Sethuraman, R. Rameshbabu, and K. Ramamurthi

1036

High pressure structural phase transition of EuS Ritu Dubey, Sadhna Singh, and Madhu Sarwan

1038

Reflectance contrast spectroscopy for distinguishing between monolayer and bilayer graphene Nihit Saigal and Sandip Ghosh

1040

Photoluminescence and defects in ultrathin SnO2 films Shikha, D. K. Pandya, and S. C. Kashyap

1042

Theoretical study of the optical behavior of HgAl2Se4 Poonam Singh, Monika Sharma, and U. P. Verma

1044

Optical properties and defect related measurement of SnO2 cauliflower Dipa Dutta and D. Bahadur

1046

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Role of indium in highly crystalline ZnO thin films Anil Singh, Sujeet Chaudhary, and Dinesh K. Pandya

1048

Photoresponse study on transition metal (Co, Ni, Mn) doped ZnO thin films R. Rajalakshmi and S. Angappane

1050

Electronic specific heat of armchair graphene nanoribbons: Effect of subbands A. S. Nissimagoudar and N. S. Sankeshwar

1052

Strain profile in GaN/AlGaN nano-heterostructure Sapna Gupta, F. Rahman, and P. A. Alvi

1054

Thermo-elastic and ductile properties of Samarium chalcogenides at high pressures A. K. Baraiya, G. S. Raypuria, and D. C. Gupta

1056

Improvement in the thermoelectric properties of Zn4Sb3 induced by Sb deficiency Anup V. Sanchela, Ajay D. Thakur, and C. V. Tomy

1058

Chalcogen doping at anionic site: A scheme towards more dispersive valence band in CuAlO2 Nilesh Mazumder, Dipayan Sen, and Kalyan Kumar Chattopadhyay

1060

Elastic constants and pressure derivative of elastic constants of Si1�xGex solid solution A. R. Jivani, J. K. Baria, P. S. Vyas, and A. R. Jani

1062

Electrical properties of solution processed highly transparent ZnO TFT with organic gate dielectric Nirav C. Pandya, Nikhil G. Joshi, U. N. Trivedi, and U. S. Joshi

1064

Surface and morphological studies of pure and Sb doped thin film gas sensors Archana Gupta, P. Rajaram, and M. C. Bhatnagar

1066

K. SUPERCONDUCTIVITY, MAGNETISM AND SPINTRONICS

Structural, transport and elastic properties of LaTiO3 Renu Choithrani, Masroor Ahmad Bhat, and N. K. Gaur

1068

Inverse magnetocaloric effect in Ce(Fe0.96Ru0.04)2: Effect of fast neutron irradiation

V. Dube, P. K. Mishra, A. K. Rajarajan, C. L. Prajapat, P. U. Sastry, S. V. Thakare, M. R. Singh, and G. Ravikumar

1070

Magnetic transition in CaFe2As2 studied via hyperfine field measurements for 66Ga by TDPAD technique S. K. Mohanta, S. M. Davane, Neeraj Kumar, A. Thamizhavel, and S. N. Mishra

1072

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Effect of annealing on the structural, microstructural and magnetic properties in Ni46Co4Mn38Sb12 ribbons Roshnee Sahoo, D. M. Raj Kumar, D. Arvindha Babu, K. G. Suresh, and M. Manivel Raja

1074

Magnetic and transport studies in Co2TiGa alloy Lakhan Pal, K. G. Suresh, and A. K. Nigam

1076

Influence of band Jahn-Teller distortion on the magnetoresistance in manganites L. Haritha, G. Gangadhar Reddy, and A. Ramakanth

1078

Development of ferromagnetic Co1.5Fe1.5O4 ferrite by varying pH value during chemical co-precipitation R. N. Bhowmik and A. Bharathi

1080

Prussian blue based molecular magnet K0.3Mn2.85[Cr(CN)6]2��nH2O with ferrimagnetic ordering temperature of 60 K Pramod Bhatt, Ranu Bhatt, M. D. Mukadam, and S. M. Yusuf

1082

Electron phonon interaction in Hubbard model S. Nath, N. S. Mondal, N. K. Ghosh, and S. K. Bhowmick

1084

Magnetic properties of Cu70.9Al18.1Mn11 alloy S. Chatterjee and S. Majumdar

1086

Magnetic investigation of Ni50Mn33In12Ga5 alloy S. Pramanick, S. Chatterjee, and S. Majumdar

1088

Study of magnetocaloric effect in GdRhIn compound Sachin B. Gupta and K. G. Suresh

1090

Electrical transport and magnetic properties of superconducting Mo52Re48 alloy Shyam Sundar, L. S. Sharath Chandra, V. K. Sharma, M. K. Chattopadhyay, and S. B. Roy

1092

Magnetization and neutron diffraction study of Tb0.9Y0.1MnO3

Keka R. Chakraborty, R. Shukla, M. D. Mukadam, S. D. Kaushik, A. K. Tyagi, V. Siruguri, and S. M. Yusuf

1094

Structural and Mössbauer spectroscopic study of cubic phase hydrogen storage alloys Ti2Nb1�xFex S. S. Meena, Priyanka Das, A. Kumar, S. Banerjee, C. G. S. Pillai, and S. M. Yusuf

1096

High coercivity through texture formation in SmCo5/Co multilayers P. U. Sastry, P. K. Mishra, M. Krishnan, P. Chowdhury, and G. Ravikumar

1098

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xlvi

Half metallic ferromagnetism in ACaB (A = Li, Na and K) compounds-DFT study R. Umamaheswari, M. Yogeswari, and G. Kalpana

1100

Fermi surface studies of Co-based Heusler alloys: Ab-initio study Swetarekha Ram and V. Kanchana

1102

Superconductivity in BiS2 based Bi4O4S3 novel compound Shiva Kumar Singh, Anuj Kumar, Shruti, G. Sharma, S. Patnaik, M. Husain, and V. P. S. Awana

1104

Bulk superconductivity at 5K in NdO0.5F0.5BiS2 Rajveer Jha, Anuj Kumar, Shiva Kumar Singh, and V. P. S. Awana

1106

Study of magnetic properties of spin-dependent Falicov-Kimball model on a triangular lattice Sant Kumar, Umesh K. Yadav, Tulika Maitra, and Ishwar Singh

1108

Structural and magnetic ordering in Co2MnSi films on (001) SrTiO3 Himanshu Pandey, P. C. Joshi, and R. C. Budhani

1110

Exchange bias effect in Co(Cr0.925Fe0.075)2O4 R. Padam, Swati Pandya, S. Ravi, A. K. Grover, and D. Pal

1112

Frustrated non-collinearity in the magnetic behaviour of layered VX2 [X = Cl, Br, I] systems A. H. M. Abdul Wasey, D. Karmakar, and G. P. Das

1114

Magnetocaloric properties of Ni2+xMn1�xSn Heusler alloys M. D. Mukadam, Pramod Bhatt, and S. M. Yusuf

1116

Study of transport and magnetic properties in new BiS2 based layered LaO0.5F0.5BiS2 superconductor Shruti, Anuj Kumar, Rajveer Jha, S. Patnaik, and V. P. S. Awana

1118

Investigation of junction magnetoresistance in Co0.65Zn0.35Fe2O4/p-Si heterostructure for spintronics J. Panda and T. K. Nath

1120

Possibility of spatial inversion symmetry breaking by magnetic ordering in Y2CoMnO6 G. Sharma, J. Saha, and S. Patnaik

1122

Neutron diffraction studies on cobalt substituted BiFeO3 J. Ray, A. K. Biswal, S. Acharya, P. D. Babu, V. Siruguri, and P. N. Vishwakarma

1124

Temperature dependence of magnetotransport behavior and its correlation with inter-particle interaction in Cu100�xCox granular films Dinesh Kumar, Sujeet Chaudhary, and Dinesh K. Pandya

1126

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Dynamical structure factor of Fulde-Ferrell-Larkin-Ovchinnikov superconductors Arghya Dutta and Jayanta K. Bhattacharjee

1128

Structural and magnetic studies of Al3+ doped cobalt ferrites CoFe2�xAlxO4 (x=0.0, 0.2, 0.4) Rabia Pandit, Pawanpreet Kaur, K. K. Sharma, and Ravi Kumar

1130

Structure and magnetism of FeMnO3 S. Rayaprol, S. D. Kaushik, P. D. Babu, and V. Siruguri

1132

Magnetic properties of GdT0.17Sn2 (T = Co, Cu) compounds Krishanu Ghosh, Chandan Mazumdar, R. Ranganathan, and S. Mukherjee

1134

Strong correlations in the two-dimensional extended Holstein-Hubbard model I. V. Sankar and Ashok Chatterjee

1136

Temperature dependent spin injection properties of self-assembled epitaxial Ni nanoparticles embedded metallic TiN matrix/p-Si heterojunction J. Panda and T. K. Nath

1138

Stability of high spin polarization via substituting spelement in Co2MnSn1�xGax Heusler alloys Mukhtiyar Singh, Hardev S. Saini, and Manish K. Kashyap

1140

Magnetic and transport relaxation property of La0.85Sr0.15CoO3 single crystals Kaustuv Manna, D. Samal, Suja Elizabeth, and P. S. Anil Kumar

1142

Effect of Pt layer thickness on perpendicular magnetic anisotropy in ultrathin Co/Pt multilayers P. D. Kulkarni, M. Krishnan, H. C. Barshilia, and P. Chowdhury

1144

Structural and magnetic properties of dispersed nickel ferrite nanoparticles synthesized through thermal decomposition route Bhaskar Chandra Behera, Ravindra A. Venkata, Chandan Srivastava, and Prahallad Padhan

1146

Synthesis and characterization of barium hexagonal ferrite M. Manikandan and C. Venkateswaran

1148

Destruction of magnetic frustration by a partial replacement of Ca by Gd in a spin chain compound Ca3Co2O6 Tathamay Basu, Kartik K. Iyer, P. L. Paulose, and Echur V. Sampathkumaran

1150

Development of multichannel MEG system at IGCAR

N. Mariyappa, C. Parasakthi, K. Gireesan, S. Sengottuvel, Rajesh Patel, M. P. Janawadkar, T. S. Radhakrishnan, and C. S. Sundar

1152

Study of quaternary Heusler alloy Co2CrAl1�xSix K. Seema and Ranjan Kumar

1154

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Electronic band structure of LaO1�xFxBiS2: A recently invented family of superconductors Jagdish Kumar, P. K. Ahluwalia, and V. P. S. Awana

1156

Single crystals of iron chalcogenide superconductor FeCr0.02Se: Growth, characterization and vortex pinning properties Anil K. Yadav, Ajay D. Thakur, and C. V. Tomy

1158

Sintering effect on structural and magnetic properties of Ni0.6Zn0.4Fe2O4 ferrite

Manoj M. Kothawale, R. B. Tangsali, G. K. Naik, J. S. Budkuley, Sher Singh Meena, and Pramod Bhatt

1160

Effect of europium substitution on the magnetic and optical properties of nanostructured bismuth ferrite A. Tamilselvan, M. Sakar, C. Nayek, P. Murugavel, and S. Balakumar

1162

Exchange bias in ball-milled LaFeO3 S. D. Kaushik, S. Rayaprol, P. D. Babu, and V. Siruguri

1164

A study on pulsed laser deposited metallic spin valves Sayak Ghoshal and P. S. Anil Kumar

1166

Exchange bias and its tuning in magnetic compensated Nd doped ferromagnetic samarium metal Swati Pandya, S. Ramakrishnan, and A. K. Grover

1168

Improved magnetic properties of microwave processed Mn0.5Zn0.5Fe2O4 particles T. Suneetha, Subhash C. Kashyap, and Hem C. Gupta

1170

Thickness dependence ferromagnetic resonance in Ta/Ni81Fe19 bilayer nanostructures Nilamani Behera, Sujeet Chaudhary, and Dinesh K. Pandya

1172

Vortex pinning mechanism in single crystal of iron arsenide superconductor SrFe1.7Co0.3As2 Ajay D. Thakur, A. K. Yadav, A. Thamizhavel, C. V. Tomy, S. Ramakrishnan, and A. K. Grover

1174

Search for ferromagnetism in transition metal doped monoclinic HfO2 K. Seema and Ranjan Kumar

1176

Magnetoresistance investigations in exchange-biased IrMn/NiFe bilayers Himanshu Fulara, Sujeet Chaudhary, and Subhash C. Kashyap

1178

Fingerprint for flux line lattice melting in a very weakly pinned crystal of 2H-NbSe2 Ulhas Vaidya, S. Ramakrishnan, and A. K. Grover

1180

Evolution of microstructure during formation of Nb3Sn superconducting phase

A. K. Singh, Shivendra Kumar, Satya Prakash Pasi, A. Laik, M. M. Hussain, K. K. Abdulla, and G. K. Dey

1182

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L. NOVEL MATERIALS

Specific heat of Pr0.5A0.5CoO3 (A=Ca and Sr) N. K. Gaur, Rasna Thakur, Rajesh K. Thakur, and A. Srivastava

1184

Lifshitz transition in bi-layer graphene Ajay Pratap Singh Gahlot

1186

Temperature and pressure dependent thermodynamical properties of uranium dinitrides: UN2 Swarna Shriya, S. Chaudhary, M. Varshney, and Dinesh Varshney

1188

Effects of sintering temperature variation on microstructure and magnetic nature of Al diluted La0.7Ca0.3MnO3 Manish Kumar, R. J. Choudhary, and D. M. Phase

1190

Synthesis of gadolinium silicate by hydrothermal method Seema Shinde, M. Ghosh, Shashwati Sen, S. G. Singh, S. C. Gadkari, and S. K. Gupta

1192

Spin momentum density of Nd using Compton spectroscopy Jagrati Sahariya, Shailja Tiwari, Alpa Dashora, H. S. Mund, M. Itou, Y. Sakurai, and B. L. Ahuja

1194

Soft ferromagnetism and semiconductor to metal transition in Li0.5Mn0.5Fe2O4 ferrite G. Vijayasri and R. N. Bhowmik

1196

Synthesis of novel multiferroic composite film of MnFe2O4-poly (vinylidene-fluoride)-BaTiO3 Amit Kumar and K. L. Yadav

1198

Effect of Fe incorporation on the optical behavior of ZnO thin films prepared by sol-gel derived spin coating techniques R. Ajay Rakkesh, R. Malathi, and S. Balakumar

1200

Crossover from more to less ordered vortex state on field-cooling a weakly pinned crystal of Ca3Rh4Sn13 Santosh Kumar, C. V. Tomy, A. K. Grover, G. Balakrishnan, and D. McK Paul

1202

Rietveld refinement and FTIR analysis of bulk ceramic Co3�xMnxO4 compositions P. L. Meena, Ravi Kumar, and K. Sreenivas

1204

Effect of variation of tin concentration on the properties of Cu2ZnSnS4 thin films deposited using chemical spray pyrolysis V. G. Rajeshmon, Abin Kuriakose, C. Sudha Kartha, and K. P. Vijayakumar

1206

Specific heat and thermal expansion of GdCoO3 N. K. Gaur, Rasna Thakur, and Rajesh K. Thakur

1208

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Raman and AFM study of gamma irradiated plastic bottle sheets Yasir Ali, Vijay Kumar, R. G. Sonkawade, and A. S. Dhaliwal

1210

Conductivity studies on PEMA based polymer electrolyte system with LiClO4 salt S. Rajendran, K. Senthil, K. Kesavan, Chithra M. Mathew, and T. Mahalingam

1212

Role of magnetostriction in magnetoelectric properties of NdCrTiO5 J. Saha, G. Sharma, and S. Patnaik

1214

Sonochemically precipitated spinel Co3O4 and NiCo2O4 nanostructures as an electrode materials for supercapacitor N. Padmanathan and S. Selladurai

1216

Electromagnetic absorption and shielding behavior of polyaniline-antimony oxide composites Muhammad Faisal and Syed Khasim

1218

Structural and piezoelectric properties of BiFeO3 thin films prepared by spin coating method R. Kennedy, D. Sornadurai, K. Ganesan, and J. Jebaraj

1220

Photonic aspect of sea shell Aditi Sarkar, Arnab Gangopadhyay, and A. Sarkar

1222

Linear and nonlinear properties of L-histidinium dinitrate S. Arulmozhi, M. Dinesh Raja, and J. Madhavan

1224

Luminescence properties of novel NaSrB5O9:Eu3+ phosphor G. R. Dillip and B. Deva Prasad Raju

1226

Effect of conventional and microwave sintering on ceramic BiFeO3 K. Rama Obulesu and K. C. James Raju

1228

Synthesis structural and luminescence analysis of NaGd1�xTbx(WO4)2 solid solution for white LED application A. Durairajan, D. Thangaraju, D. Balaji, and S. Moorthy Babu

1230

Single phase synthesis and room temperature neutron diffraction studies on multiferroic PbFe0.5Nb0.5O3 Shidaling Matteppanavar, Basavaraj Angadi, and Sudhindra Rayaprol

1232

Synthesis and characterization of Eu3+:YAG nanopowder by precipitation method D. Balaji, D. Thangaraju, A. Durairajan, and S. Moorthy Babu

1234

Shape controlled synthesis of Cu2O microcrystals and their structural and optical properties G. Prabhakaran and Ramaswamy Murugan

1236

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Low temperature dielectric properties of YMn0.95Ru0.05O3 Rajesh K. Thakur, Rasna Thakur, G. S. Okram, N. Kaurav, and N. K. Gaur

1238

Double negative refraction in barium substituted magnesium ferrite in the microwave frequency region P. Chithra lekha, S. Dinesh Kumar, N. Yogesh, and V. Subramanian

1240

Mechanically strained tuning of the electronic and dielectric properties of monolayer honeycomb structure of tungsten disulphide (WS2) Ashok Kumar, Brij Mohan, Arun Kumar, and P. K. Ahluwalia

1242

Combustion synthesis of novel boron carbide R. Saai Harini, E. Manikandan, S. Anthonysamy, V. Chandramouli, and D. Eswaramoorthy

1244

Topographical studies on GNF crystals of non linear optical origin M. M. Khandpekar and S. P. Pati

1246

Structural studies of Na4(ThxU1�x)(MoO4)4 (x = 0.5, 0.8) N. D. Dahale, S. K. Sali, Meera Keskar, Rohan Phatak, and S. Kannan

1248

Synthesis of Ag coated Cr4+/Cr3+ nanocomposites by mechanical attrition method M. Patange, J. Jadhav, and S. Biswas

1250

First principle calculation of bulk electronic properties of cubic SrMO3 perovskites (M = Ti, Zr) Avinash Daga, Smita Sharma, and K. S. Sharma

1252

The effect of Pr co-dopant in samarium doped ceria V. Venkatesh, V. Prashanth Kumar, Y. S. Reddy, and C. Vishnuvardhan Reddy

1254

Diffuse phase transition in Li0.12Na0.88NbO3 piezoelectric ceramics Supratim Mitra, Ajit R. Kulkarni, and Om Prakash

1256

Effects of chemical disorder on magnetism in inverse Heusler alloy Mn2NiSn Souvik Paul and Subhradip Ghosh

1258

Study of de-watering from the gelatinous precipitate formed during co-precipitation of Nd-YAG powder Sanjib Karmakar, Rachna Sharma, S. K. Pathak, S. M. Gupta, and P. K. Gupta

1260

Raman studies of chemically and thermally reduced graphene oxide Madhusmita Sahoo, Rajini P. Antony, Tom Mathews, S. Dash, and A. K. Tyagi

1262

Synthesis and structural characterization lithium nickel oxide at different temperatures K. Vijaya Babu, V. Veeraiah, P. S. V. Subba Rao, and Paulos Taddesse Shibeshi

1264

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Studies on PEO-BMImHSO4 solid polymer electrolyte S. S. Pundir, Kuldeep Mishra, and D. K. Rai

1266

Magnetic and ferroelectric studies of double perovskite (KBi)(FeNb)O6 ceramics

B. K. Choudhary, A. K. Himanshu, Uday Kumar, S. K. Bandyopadhayay, Pintu Sen, S. N. Singh, and T. P. Sinha

1268

Structural and multiferroic properties of YMnO3 ceramics synthesized by co-precipitation method M. Muneeswaran, C. Mascovani, and N. V. Giridharan

1270

Growth and characterization of potassium acid phthalte for third order NLO applications B. Sivakumar, S. Gokul Raj, G. Ramesh Kumar, and R. Mohan

1272

Magnetodielectric properties of frustrated antiferromagnet LiCrO2 A. K. Singh, K. Singh, Tathamay Basu, K. K. Iyer, P. L. Paulose, and E. V. Sampathkumaran

1274

Enhance of ferroelectric properties by modifying Pb2+ side by Mg2+ in PZT (52/48) ceramics P. Kour, Pawan Kumar, Manoranjan Kar, and S. K. Sinha

1276

Optical and dielectric properties of TiO2 doped PVA-CN/LiClO4 composite electrolyte Sunil G. Rathod, R. F. Bhajantri, V. Ravindrachary, P. K. Pujari, and T. Sheela

1278

Photochromic and microstructural properties of methyl orange doped poly(vinyl alcohol) R. F. Bhajantri, Renuka Sali, V. Ravindrachary, P. K. Pujari, T. Sheela, and Sunil G. Rathod

1280

Effect of Ni doping on the structural, optical and magnetic properties of Zno Gunjan Srinet, Ravindra Kumar, and Vivek Sajal

1282

Structural and optical properties of copper zinc tin sulphide (CZTS) material synthesized using binary sulphide precursors K. K. Patel, D. V. Shah, and Vipul Kheraj

1284

Structural stability of BiFeO3 by chemical modification in Bi as well as Fe sites Chandrakanta Panda , Pawan Kumar, and Manoranjan Kar

1286

Molecular dynamics studies of radiation damage in yttria Manan Dholakia, Gurpreet Kaur, and M. C. Valsakumar

1288

Growth of fluorine doped SnO2 nanostructures by spin coating of ultrasonically prepared gel precursor Y. C. Goswami, Vijay Kumar, V. Ganesan, and P. Rajaram

1290

Structural and photoluminescence properties of Zn2SiO4:Tb3+ & Zn2SiO4:Tb3++Li+ phosphors B. Chandra Babu and S. Buddhudu

1292

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liii

Effect of chromium doping on the resistivity behavior of gadolinium manganite Anchit Modi, Rajesh K. Thakur, Rasna Thakur, G. S. Okram, and N. K. Gaur

1294

Dimensional crossover in chemical potential of synthetic spin-orbit coupled Fermi systems Reena Gupta, Dilna Azhikodan, G. S. Singh, and Jürgen Bosse

1296

Observation of dielectric and magnetic anomalies in multiferroic PbTi0.5Fe0.5O3 compound Snehlata Gupta, S. Chakrabarti, and V. R. Palkar

1298

Blue light emitting naphthalimides for organic light emitting diodes Hidayath Ulla, B. Garudachar, M. N. Satyanarayan, G. Umesh, and A. M. Isloor

1300

Preparation and characterization of NaClO4 doped poly(vinyl alcohol)/sodium alginate composite electrolyte T. Sheela, R. F. Bhajantri, V. Ravindrachary, P. K. Pujari, and Sunil G. Rathod

1302

Charge transport in a zigzag silicene nanoribbon Nakul Mehrotra, Niraj Kumar, and Arijit Sen

1304

Enhanced dielectric and ferroelectric properties of Ca2+ substituted sodium bismuth titanate Chandrahas Bharti, A. Sen, and T. P. Sinha

1306

ABSTRACTS

Synchrotron X-ray scattering studies of nanostructure-formation at interfaces Milan K. Sanyal

1308

Exploring the tunable coexistence of magnetic phases P. Chaddah

1309

Development of scintillation materials for medical imaging and other applications C. L. Melcher

1310

Strutural phase transitions in rare earth sesquioxides under pressure N. V. Chandra Shekar, A. Arulraj, N. R. Sanjay Kumar, C. Ravi, M. Sekar, and P. Ch. Sahu

1311

Fundamentals of materials, techniques and instrumentation for OSL and FNTD dosimetry M. S. Akselrod

1312

First-principles based calculation of phonon spectrain substitutionally disordered alloys Subhradip Ghosh

1313

Ultrafast interfacial charge transfer dynamics in dye-sensitized and quantum dot solar cell Hirendra N. Ghosh

1314

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liv

Improving organic solar cell efficiency by increasing light absorption and charge carrier mobility in the device active layer S. Sundar Kumar Iyer

1315

Superconducting and normal state tunnelling in NbN-GdN-NbN junctions Kartik Senapati

1316

Magnetism without magnetic atoms: The physics of the vacancy in graphene Sashi Satpathy

1317

Post-processing of lattice dynamical data for large crystalline systems (disordered semiconductors) Andrei Postnikov

1319

Multiferroic oxides: Growth of single crystals and investigation of their magnetic, dielectric and ferroelectric properties Geetha Balakrishnan

1320

Novel, band-controlled metal oxide compositions for semiconductor-mediated photocatalytic splitting of water to produce H2 Narendra M. Gupta

1321

Phase behavior and unusual dynamics of stimuli-responsive microgel colloids B. V. R. Tata

1322

Role of defect states on magnetic and electrical properties of ZnO nanostructures: An experimental view M. Aslam

1323

Semiconducting nanowire field effect transistor for nanoelectronics and nanomechanics Mandar Deshmukh

1324

Optically induced ultrafast magnetization dynamics in two-dimensional ferromagnetic nanodot lattices Anjan Barman

1325

Proteins as "dopable" bio-electronic materials David Cahen

1326

NMR study of valence fluctuating state in rare-earth based materials with multi-4f electrons Takeshi Mito

1327

Conductance and thermopower in molecular nanojunctions Arijit Sen

1328

Author Index 1329

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Preface: Solid State Physics Symposium We are happy to present the Proceedings of the Solid State Physics Symposium-2012 held at the ‘Indian Institute of Technology-Bombay’, Mumbai during December 3 - 7, 2012. The American Institute of Physics is publishing the proceedings online. This annual symposium is sponsored by the ‘Board of Research in Nuclear Sciences’ (BRNS), Department of Atomic Energy (DAE), Government of India and this is 57th in the series. The DAE-SSP Symposium is a very popular and prestigious scientific event, covering almost all aspects of solid state physics and brings together scientists and research students from all over the country. This year the number of contributed papers we received was 1623. This included 50 papers in the ‘PhD Thesis’ and 17 papers in the ‘Young Achievers Award’ categories. A panel of experts chosen from various institutes and universities across the country reviewed all the papers. After the evaluation, 778 papers were accepted for presentation in the symposium. The number of registered participants was 933 and contributed papers were presented in the poster sessions spread over four daysand 29 papers were also presented in the oral sessions. Four researchers were selected for the Young Achievers Award in this year’s symposium. Further, four awards were given in the PhD thesis category.

The symposium included contributions from leading scientists of seven countries besides the ones from premier research institutes of India. Special thematic sessions devoted to ‘Materials for energy’, ‘Soft Condensed Matter’, ‘Phonons in Disordered Systems’ and ‘Organic Photovoltaics’ accorded remarkable topicality to this symposium that was further endorsed through 778 papers screened in from the 1623 submissions.

Efficient storage of information and its reliable retrieval, health care and radiation detection, are the prime concerns of our society and the symposium addressed them with due priority by scheduling lectures on LSO:Ce and Al2O3:Mg,C systems on the opening day itself. These lectures had a distinct definitive flavor as they were delivered by inventors themselves.

Studies on temperature dependence of PL spectra of InAs quantum dots embedded in GaAs hetero-structures and its modeling, dependence of PL spectra of Ga2O3 on the desorption of oxygen and the potential of this phenomenon for detection of oxygen were some of interesting reports that appeared in this symposium. Dosimetric application of Li2B4O7:Ag system, the influence of temperature profile of furnace on scintillation yield of CsI:Tl system and successful application of first principle studies in explaining the optical properties and scintillation mechanism that operates in tungstate based material systems figured prominently in the deliberations of the symposium. Another interesting piece of work included fungus assisted synthesis of metal nano-particles.

The symposium organization owes its success to the efforts of many individuals, members of the ‘National Advisory Committee’, ‘National Organizing Committee’ and the ‘Local Organizing Committee’. We express our sincere gratitude to all of them. We thank all participants for their contributions, as also the coordinators and reviewers of the papers for sparing their valuable time and early responses. We put on record our thanks to BRNS, DAE for the financial support. We are grateful to Dr. S. Kailas, Director, Physics Group, BARC for his continued support. We are sincerely thankful to Dr. S. L. Chaplot, Head, Solid State Physics Division and Dr. S.K. Gupta, Head, Technical Physics Division, BARC, for several valuable and timely suggestions during the entire organization of this symposium. Last but not the least we thank Prof. C.V. Tomy, the Local Convener and his team members for the local arrangements and hospitality extended to all the participants of the symposium. A. K. Chauhan, Chitra Murli and S. C. Gadkari (Guest Editors)

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 1-1 (2013); doi: 10.1063/1.4790890

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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National Advisory Committee

S. Banerjee DAE Mumbai R. K. Sinha DAE/BARC Mumbai M. Barma TIFR Mumbai D. Khakhar IIT-B Mumbai K. Bhattacharyya IACS Kolkata R. C. Budhani NPL New Delhi P. Chaddah UGC-DAE-CSR Indore S. K. Joshi NPL New Delhi S. Kailas BARC Mumbai N. Kumar RRI Bangalore E. V. Sampathkumaran TIFR Mumbai A. K. Raychaudhuri SNBNCBS Kolkata A. Roy IUAC New Delhi P. D. Gupta RRCAT Indore M. K. Sanyal SINP Kolkata A. K. Sood IISc Bangalore C. S. Sundar IGCAR Kalpakkam

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National Organizing Committee

A. K. Arora IGCAR Kalpakkam D. K. Aswal BARC Mumbai S. Basu BARC Mumbai K. Bhanumurthy BARC Mumbai S. L. Chaplot (Chairman) BARC Mumbai A. K. Chauhan (Secretary) BARC Mumbai G. K. Dey BARC Mumbai S. K. Dhar TIFR Mumbai S. C. Gadkari (Convener) BARC Mumbai Aswini Ghosh IACS Kolkata A. GhoshRoy SINP Kolkata A. K. Grover TIFR Mumbai S. C. Gupta BARC Mumbai S. K. Gupta BARC Mumbai D. C. Kothari Mumbai Univ. Mumbai G. P. Kothiyal BARC Mumbai R. Lavanya BARC Mumbai S. S. Major IIT-B Mumbai Chitra Murli (Secretary) BARC Mumbai R. Mittal BARC Mumbai R. Mukhopadhyay BARC Mumbai C. Muthamizchelvan SRM Univ. Kattankulathur S. B. Roy RRCAT Indore Sangeeta BRNS Mumbai B. R. Sekhar IOP Bhubaneshwar S. M. Sharma BARC Mumbai V. Siruguri UGC-DAE-CSR Mumbai K. G. Suresh IIT-B Mumbai C. V. Tomy (Local Convener) IIT-B Mumbai P. B. Vidyasagar Pune University Pune S. M. Yusuf BARC Mumbai

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TOPICS

a. Phase Transitions b. Soft Condensed Matter including Biological Systems c. Nano-materials d. Experimental Techniques & Devices e. Liquids, Glasses & Amorphous Systems f. Surfaces, Interfaces & Thin Films g. Electronic Structure & Phonons h. Single Crystals i. Transport Properties j. Semiconductor Physics k. Superconductivity Magnetism and Spintronics l. Novel Materials

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Review Coordinators

Dr. S. N. Achary Dr. Ranjan Mittal

Dr. V. K. Aswal Dr. P. Modak

Dr. Saibal Basu Dr. K. P. Muthe

Dr. Shovit Bhattacharya Dr. K. K. Pandey

Dr. A. Bharathi Dr. Rekha Rao

Dr. A. K. Debnath Dr. Mala N. Rao

Dr. Alka Garg Dr. A. K. Rajarajan

Dr. V. Ganesan Dr. Rajul Ranjan

Dr. M. Ghosh Dr. Debasis Sen

Dr. Mukul Gupta Dr. Shashwati Sen

Dr. P. A. Hassan Dr. Ajay Singh

Dr. Manmeet Kaur Dr. Meenakshi Sunder

Dr. D. Karmakar Dr. V. Sudarshan

Dr. P. K. Mishra Dr. J. C. Vyas

Dr. Subhankur Mitra

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Connecting Jamming and Depinning Transitions

C. Reichhardt1, Z. Nussinov2, and C.J. Olson Reichhardt1

1Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA, [email protected]

2Department of Physics, Washington University, St. Louis, Missouri 63160, USA

Abstract. We examine a system of binary disks that is known to exhibit a jamming transition at a well defined density termed point J. We add quenched disorder and measure the external force needed to depin the disks or send them into motion as a function of disk density. We find a rich variety of depinning behaviors. For small amounts of disorder, only the jammed or stiff phases are pinned. For strong disorder, disks in unjammed samples with densities well below jamming are more strongly pinned than disks in samples at densities close to the jamming transition. We also discuss connections to the peak effect for depinning in vortex systems.

Keywords: jamming, pinning, peak effect, granular matter PACS:74.25.Wx, 74.25.Uv

INTRODUCTION

The jamming that occurs in loose assemblies of repulsive particles, such as disordered packings of disks or grains, has been extensively studied in the context of increasing density [1-5]. At low densities, few of the particles are touching each other, and the system acts like a fluid with no shear modulus. At high densities, the system gains a shear modulus and acts like a solid in a state that is termed “jammed.” Unlike solidification, jamming can occur without the development of long range order or crystallization. In two dimensions, one of the best studied jammed systems is a bidisperse assembly of disks with a short range repulsive interaction and radii ra and rb [2,3,5]. At a radius ratio of ra/rb=1.4, the system jams when the area covered by the disks is �j=0.844. Here we study how such a system responds to an external drive when quenched disorder or pinning sites are added to the sample. The particular question we address is how the depinning transition changes as we cross �j as a function of the density of pinning sites. It may be thought that a stiff system might be easier to pin since in the case of an elastic solid, it is only necessary to hold down a portion of the sample and due to the strong interactions the rest of the sample will remain immobilized. On the other hand, in a liquid-like system, only a small portion of the system may be pinned by quenched disorder while the remaining particles flow past the pinning sites. Studies of depinning of vortices in type-II superconductors,

which can be viewed as discrete particles with repulsive interactions moving through quenched disorder, have found that the opposite can sometimes be true [6,7,8]. This is more understandable in the limit where there are many pinning sites. An elastic solid cannot easily adjust to such a substrate, so not all the particles will sit at pinning sites. Conversely, in a liquid-like or unjammed system, the particles can easily adjust their positions to take advantage of the substrate minima, resulting in strong pinning. Here we demonstrate that granular disk systems interacting with disorder can exhibit both types of depinning behavior.

SIMULATION

We consider a binary disk system in two dimensions with periodic boundary conditions in the x and y directions. The disks are modeled as harmonically repulsive objects with a repulsion that drops to zero at a radius r. We use a bidisperse assembly of disks with radius ratio ra/rb=1.4 that has previously been shown to exhibit a transition to an elastic solid or jammed phase at an area coverage of �j=0.844.

The dynamics of disk i are obtained by integrating the following overdamped

equation:η

dRidt =Fi

in+Fivp +Fd .

Here � is the damping constant which is set equal to unity. The disk-disk interaction force is Fi

in. The

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 7-10 (2013); doi: 10.1063/1.4790891

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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pinning force Fivp is modeled as originating from

randomly located short range attractive parabolic wells that each have a radius smaller than the radius of the smaller disks. The external driving force Fd is modeled as a uniform force applied to all the disks that starts at zero and is slowly increased in small increments. We measure the resulting total velocity of all disks in the system and construct a velocity-force curve, where a pinned phase is defined as a regime with a steady state velocity value of V=0. We define the pinning filling fraction as the number Np of pinning sites divided by the number of disks Nj at the pin-free jamming density. The pinning sites all have a maximum force of Fp, so that in the single disk limit the system is in motion for Fd > Fp.

RESULTS

In Fig. 1 we show the velocity-force curves for three different cases. In a system with a low pinning density, Np/Nj=0.093, at a disk density of �/�j=0.95 below the pin-free jamming density, Fig. 1(a) shows that there is a steady state finite velocity response even at very low Fd, indicating that the system is not pinned. In this case the system acts like a liquid with zero shear modulus. The few pinning sites can capture some of the disks, but there is ample room for the other disks to move freely past the pinned disks. The motion of the disks in this case is plastic, with some disks moving while other disks remain pinned. This leads to a bimodal velocity distribution similar to that observed for superconducting vortices in the plastic flow regime [6]. The velocity-force curve is linear at low drives since the number of disks that are not moving is equal to the number of pinning sites. At large drives, the curve becomes nonlinear and goes as V ∝Fd

βwith β≈1.5. This occurs in the regime

where some of the particles depin from the pinning sites for a certain amount of time before being pinned again. As the drive increases, the amount of time they spend unpinned becomes longer. This nonlinear behavior in the plastic flow regime has also been observed in plastic depinning [9,10,11,12]. The two-step depinning process consisting of a linear regime at low drives followed by a nonlinear regime at high drives has also been observed in simulations of systems with large voids, where the initial flow occurs in a few well-defined channels that contain a fixed number of moving particles, while at higher drives additional particles become depinned [10]. For this same pinning density, when � is increased the disks can flow for arbitrarily low Fd.

In Fig. 1(b) we illustrate the velocity-force curves for the same pinning density but with �/�j=0.99, just below the jamming density. In this case, there is a

well-defined depinning threshold at Fd=0.039. Additionally, the velocity-force curve has a completely different shape than that of the lower filling shown in Fig. 1(a). Above the sharp jump, the velocity-force

curve can be fit by V ∝Fdβ

with β=0.5. A similar behavior has been observed in experiments and simulations of systems that exhibit elastic depinning [9]. In elastic depinning, all of the particles move as a solid unit without undergoing plastic deformations. In the system illustrated in Fig. 1(b), the flow is also elastic and the disks do not exchange any neighbors while they move. Since the jammed phase acts like an elastic solid, it is reasonable to expect the depinning in this regime to be elastic. The reason that the depinning threshold is finite is that since the system now has a finite shear modulus, a few disks can be directly pinned by the pinning sites, and in the solid phase these pinned disks can hold the entire system in place. In this work we consider disks with a large spring constant for their interaction force. For softer systems it would be possible for the disks to compress, leading to a plastic depinning process; however, there would still be a finite depinning threshold, whereas at lower disk density there is no finite depinning threshold.

FIGURE 1. The velocity V of all disks vs external drive

Fd. (a) A system with a small density of pinning sites Np/Nj=0.093 at a disk density of ���j=0.95, below jamming. Here the depinning threshold is zero. (b) A system with the same pinning density but a high disk density of ���j=0.99, where there is a finite depinning threshold separating the pinned and flowing phases. (c) A system with �/�j=0.761 and a larger pinning density of Np/Nj=0.4. Here, even though the system is well below the jamming density, there is still a finite depinning threshold.

In Fig. 1(c) we show velocity-force curves for a

system well below jamming with ���j=0.761 but with a higher pinning density of Np/Nj=0.4. In this case there are still more disks than pinning sites so not all of the disks can be directly pinned; however, we still observe a finite depinning threshold and nonlinear features in the velocity-force curve. Here the depinning is plastic and above depinning only a portion of the disks are moving while other disks remain stationary.

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FIGURE 2. The depinning threshold Fc vs �/�j. (a) A

system with a small density of pinning sites Np/Nj=0.007. Here there is only a finite depinning threshold for ���j>1.0, where the depinning is elastic. (b) A system with a high pinning density of Np/Nj=0.828. Here the depinning threshold is highest for ���j<1.0.

In general we can define two regimes. The first appears in clean systems containing a small number of pinning sites, where a finite depinning threshold only occurs when the disks are acting like an elastic solid at densities that are just below the jamming transition or higher. In Fig. 2(a) we plot the value of the depinning threshold Fc versus �/�j for a system with a small fraction of pinning sites Np/Nj=0.007. Below����j=1.0, Fc=0, while Fc peaks at �/�j=1.0 and then slowly drops with increasing ��for ���j>1.0. Figure 2(b) shows Fc versus ���j for samples with a high density of pinning sites Np/Nj=0.828. In this case, Fc is highest for �/�j<1.0, below jamming, and there is a large drop in Fc just below the jamming transition. The depinning is elastic for �/�j>1 just as it is at Np/Nj=0.007.

The behavior we find for the larger pinning densities is similar to that found for the peak effect in vortex systems [6,7,8]. In the case of vortices, elastic depinning produces a lower depinning threshold, while in the soft or plastic depinning regime, the depinning threshold is higher. In the superconducting case, at higher magnetic fields when the depinning current decreases, the vortex lattice is softening with increasing magnetic field, which is the opposite of the behavior of the disk system where the shear modulus increases with increasing density. In our system, decreasing the disk density would correspond to increasing the vortex density. Our results suggest that in the vortex system there must be a high density of pinning sites. The strength of the pinning can be small but there must be a large number of pinning sites in order for a peak effect to occur. We note that for some superconducting samples with strong pinning, no peak effect is observed. This is because the pinning is so strong that it prevents elastic depinning from occurring. There are still significant differences between the two systems, such as the fact that in the disk system the elastic phase can be disordered or amorphous, while in the vortex system the elastic

phase is associated with the formation of a vortex crystalline state.

FIGURE 3. The particle positions in the pinned state.

(a) At �/�j=0.76 and Np/Nj=0.415 there are large voids in the system. (b) At ���j=1.04 and the same pinning density, the disks are uniformly distributed and the system depins elastically.

For the disk system, although the structure is

amorphous both above and below jamming, the pinned states for strong pinning contain large void regions, whereas in the jammed state the disk density is uniform. In Fig. 3(a) we illustrate the case �/�j=0.76 at Np/Nj=0.415 where large vacant regions appear when the disk density is well below jamming. Figure 3(b) shows that at �/�j=1.04 at the same pinning density, the system forms a uniform state without voids.

CONCLUSION

We examine a system of bidisperse disks that is known to exhibit a jamming transition at a well defined density. Above the jamming density, the disk assembly has a finite shear modulus that is absent below the jamming density. We specifically consider the effect of adding quenched disorder or pinning to the system, and measure the depinning threshold under an applied drive. For a small density of pinning sites, a finite depinning threshold appears only close to or above the jamming density, when the disks behave elastically. The depinning in this case is elastic, with the disks maintaining the same neighbors over time. For densities below jamming at small pinning density, the depinning threshold is zero. For systems with a high density of pinning sites, we find that the depinning threshold is highest at disk densities below jamming when the depinning is plastic, and that the depinning threshold drops sharply at the onset of jamming when the system behaves elastically. Our results show that in some cases, a system without a finite shear modulus is better pinned when the pinning density is high, while for low pinning densities, a system that is jammed or elastic is better pinned. Our results will be of interest to the fields of depinning in

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vortex matter, Wigner crystals, and other types of driven collectively interacting particles in the presence of quenched disorder.

ACKNOWLEDGMENTS

This work was carried out under the auspices of the NNSA of the U.S. DoE at LANL under Contract No. DE-AC52-06NA25396.

REFERENCES

1. A.J. Liu and S.R. Nagel, Nature (London) 396, 21 (1998).

2. C.S. O'Hern, L.E. Silbert, A.J. Liu, and S.R. Nagel, Phys. Rev. E 68, 011306 (2003).

3. T.S. Majumdar, M. Sperl, S. Luding, and R.P. Behringer, Phys. Rev. Lett. 98, 058001 (2007).

4. J.A. Drocco, M.B. Hastings, C.J. Olson Reichhardt, and C. Reichhardt, Phys. Rev. Lett. 95, 088001 (2005).

5. C.J. Olson Reichhardt and C. Reichhardt, Phys. Rev. E 82, 051306 (2010).

6. S. Bhattacharya and M.J. Higgins, Phys. Rev. Lett. 70, 2617 (1993).

7. A.C. Marley, M.J. Higgins, and S. Bhattacharya, Phys. Rev. Lett. 74, 3029 (1995).

8. C.J. Olson, C. Reichhardt, and S. Bhattacharya, Phys. Rev. B 64, 024518 (2001).

9. C. Reichhardt and C.J. Olson, Phys. Rev. Lett. 89, 078301 (2002).

10. C. Reichhardt and C.J. Olson, Phys. Rev. Lett. 90, 046802 (2003).

11. M.B. Hastings, C.J. Olson Reichhardt, and C. Reichhardt, Phys. Rev. Lett. 90, 098302 (2003).

12. C. Reichhardt, C.J. Olson Reichhardt, I. Martin, and A.R. Bishop, Phys. Rev. Lett. 90, 026401 (2003).

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Vibrational Properties of Zincblende Structured Ternary Alloys

Mala N. Rao

Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai – 400085 Email: [email protected]

Abstract. The peculiar characteristics of vibrational spectra of zinc blende semiconductor alloys arise due to either difference in masses or contrast in bond lengths. For example, previous Raman and infrared experiments have helped in identifying two mode vibrational behaviors in mixed systems of Zn1-xMgxSe and Zn1-xMgxTe in contrast to the one-mode behavior in Zn1-xMgxS. Our lattice dynamics computations, and inelastic neutron scattering experiments have elucidated that in addition to the mass of the anion and bond length anomalies, energy separation between the two sets of optical modes, and the magnitudes of the scattering cross section play an important role in the observance of one mode behavior in the S system, two mode behavior for the whole of the composition range in the Se and Te systems, and an additional Be-Te or Be-Se or Zn-Se-like vibrational doublet in case of Zn1-xBexTe, and Zn1-xBexSe. Our calculations incorporate the treatment of disorder through a supercell approach. The calculated lattice constants for different concentrations, the bimodal bond length distribution, as well as the phonon frequencies at the Brillouin zone centre are in good agreement with the available experimental data.

Keywords: lattice dynamics, semiconductors, phonons, Raman spectra PACS: 63.20.-e, 63.20.D-, 63.20.dd, 78.30.Fs

INTRODUCTION

The II-VI semiconductors ZnSe, ZnS and ZnTe constitute a family crystallizing in the cubic zincblende structure at ambient pressure, and are of technological interest as light-emitting diodes and laser diodes [1]. The study of vibrational spectra of any crystalline material typically constitutes the determination of the characteristic properties of its normal modes (phonons), experimentally measurable through their interaction with radiation, for example, Raman scattering and inelastic neutron scattering (INS). The frequencies of the optical modes (longitudinal optic (LO) and transverse optic (TO)) at the Brillouin zone centre (BZC) are accessible by Raman scattering experiments, whereas the complete phonon dispersion relation or the phonon density of states may be determined by INS experiments. The vibrational properties of these parent compounds have been well studied, but the high pressure phase transitions still have some open questions [2, 3].

The ternary compounds Zn1-xMgxSe, Zn1-xMgxTe, Zn1-xMgxS have gained importance for technological applications due the possibility of the tuning of band-gap energy, whereas Zn1-xBexSe and Zn1-xBexTe provide the additional possibility that the highly ionic

soft parent lattices may be strengthened so as to reduce defect propagation, and hence increase the lifetime of the devices. However, the vibrational properties of these compounds are intriguing because of the lack of understanding of the variety in behavior of the phonon modes that can arise due to change in composition.

Through Raman and infrared scattering methods, typically two types of phonon mode behavior are observed in compounds of the type A1-xBxC. In the first type, two optic phonons are observed at the BZC, with the frequencies varying linearly with concentration from the frequency characteristic of one end member to that of the other end member. This one mode behavior is fully understood under the Virtual Crystal Approximation (VCA). In the second type, two phonon frequencies are observed for each of the allowed optic modes of the pure crystal at frequencies close to that of the end members-that is, two AC-like and two BC-like modes. This behavior is explained by the empirical modified random element isodisplacement (MREI) model [4], as a phenomenon resulting from the contrast in masses of the elements forming the compounds. For example, experiments [5] have identified two-mode behavior in Zn1-xMxSe and Zn1-xMgxTe, and the MREI model predicts one-mode behavior in Zn1-xMgxS.

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 11-14 (2013); doi: 10.1063/1.4790892

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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But the recent studies [6] on Be alloys threw up some interesting results, in that the optic modes showed additional modes (one Be-C LO-TO doublet), which did not follow the MREI classification (two Be-C and two Zn-C modes). The results presented in this work are an attempt to understand the peculiarities of these modes.

METHODOLOGY

A combination of INS experiments and lattice dynamics computations was employed to gain a microscopic understanding of the vibrational properties of the mixed crystals. Both phonon dispersion curves as well as phonon density of states may be determined using INS, if single crystalline and polycrystalline samples are available. For the lattice dynamical calculations, the software DISPR [7] was used, which employs a parametrized interatomic potential model with terms representing Coulomb, short range and van der Waals interactions. For these calculations, the treatment of disorder was incorporated through a supercell approach.

RESULTS AND DISCUSSION

The lattice dynamical computations on the parent compounds (ZnSe, ZnS, ZnTe) provided a good description [8] of the Raman frequencies, both at ambient pressure as well as at high pressures. The phonon dispersion relation, the phonon density of states as well as the equation of state (zincblende-to-rocksalt at pressures around 10-15 GPa) was reproduced fairly well. The calculations were also able to give an insight into the negative thermal expansion and non-Debye specific heat (Figure 1) in these compounds.

0 100 200 3000

10

20

30

40

50

100 200 300

0

3

6

20 400.0000

0.0002

0.0004

Cp/T

3 (J/m

olK4 )

T(K)

Cp(J

/K/m

ole)

Calculated Experimental

ZnSe

T (K)

�(10

6 K1 )

T(K)

Calculated Experimental

ZnSe

FIGURE 1. Negative thermal expansion and non-Debye specific heat in ZnSe[8].

Computation of the phonon frequencies as a

function of pressure elucidated that the SC16 phase

had instabilities [8] (Figure 2) which would impede its

0 2 4 6-70i

-35i

0

35

Freq

uenc

y (c

m-1)

P (GPa)

ZnSe (SC16 phase)

q=(0.5 0.5 0.5)

q=(0 0 0.5)

FIGURE 2. Phonon instability in SC16 phase of ZnSe[8].

existence as a stable phase between the two known phases, as predicted by ab initio enthalpy calculations [3], but not observed experimentally.

In the ternary alloy Zn1-xBexSe (x=0.33), INS experiments carried out on single crystalline samples helped to map out the phonon dispersion relation along the three symmetry directions, as well as confirm that (i) collective excitations were defined throughout the whole Brillouin zone, and (ii) an additional LO-TO doublet persists right up to the Brillouin zone boundary. This is confirmed by the presence of double peaks in the INS spectrum (Figure 3), and is consistent with results from Raman scattering as well as the interpretation [6, 9] as being due to

50 55 60 65 70 75 80

80

120

160

200Q=(4,2.2,2.2)q=0.2[011]

coun

ts/ 5

min

Energy (meV)

FIGURE 3. Typical INS spectrum of single crystalline Zn0.67Be0.33Se measured at the phonon wavevector q and the reciprocal lattice point Q. differences in the local neighbourhood of the Be-Se bonds. The reciprocal lattice points for the measurement of the LO and TO phonon modes were chosen by an examination of the computed neutron scattering cross sections. Further, INS experiments to determine the phonon density of states (PDOS) in this mixed crystal, using polycrystalline samples, confirmed the validity of the potential model (Figure 4) through the well reproduced spectral features obtained by the computations.

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0 20 40 60 80 100

PD

OS

(arb

. uni

ts)

Energy (meV)

experimental calculated

FIGURE 4. INS spectrum of polycrystalline Zn0.67Be0.33Se along with the computed neutron weighted phonon density of states. The main results from the lattice dynamical calculations were the following:

Bimodal bond length distribution

In all the compounds studied (Zn1-xMgxSe, Zn1-xMgxS, Zn1-xMgxTe, Zn1-xBexTe, Zn1-xBexSe), a bimodal bond length distribution could be identified with variation in composition i.e two distinct bond lengths are observed, each corresponding to the two different cation-anion distances. Again, for any particular composition, the distribution of Mg-anion, as well as Zn-anion (anion=S, Se, Te) bond lengths shows a one-peak structure [10] whereas Zn-Te and Be- Te bond lengths in ZnBeTe [10] and ZnBeSe [11] show more than one peak.

Phonon frequencies at Brillouin zone centre

The computation of the one phonon inelastic scattering cross section [10] enabled us to identify the phonon frequencies at BZC. The calculated phonon frequencies show good agreement with data from Raman and infrared scattering experiments. Further, as Figure 5 shows, one mode behavior in Zn1-

xMgxS and two mode behavior in Zn1-xMgxTe is very clearly demarcated through the cross sections. In addition, for Zn1-xMgxS, the presence [10] of non-zero cross sections (though low) for modes in the gap between the acoustic and optic regions suggests a multi-mode behavior, in contrast to Chang and Mitra’s criterion [4]. Comparison of the phonon frequencies, the range of the spectrum, as well as the cross section of

30 40 500

20

40

60

20 24 28 32 360

20

40

60

Energy (meV)

Cros

s-se

ctio

n

LO (MgTe-like)

TO (MgTe-like)

LO (ZnTe-like)TO

(ZnTe-like)

Cros

s-se

ctio

n

Energy (meV)

Zn1-xMgxTe; x=0.4

Zn1-x

MgxS; x=0.4 LO

TO

FIGURE 5. Computed one phonon inelastic scattering cross section for Zn1-xMgxTe and Zn1-xMgxS (x=0.4)[10]. Zn1-xMgxTe (which has a two-mode behavior [5]) and Zn1-xBexTe, (which has a multi-mode behavior [6]) showed that energy separation between the modes too, is an important factor which helps to understand the pattern of behavior in these mixed crystals.

SUMMARY

In summary, inelastic neutron scattering measurements confirmed the presence of an additional Be-Se vibrational doublet in Zn1-xBexSe, in confirmation with results from Raman scattering experiments, and its interpretation as being due to changes in the environment local to the Be-Se bond, whereas lattice dynamical computations suggested [10] that in addition to reduced mass of the two sub lattices (Chang and Mitra’s criterion[4]), bond length anomalies, energy separation between the two sets of optical modes and magnitudes of the scattering cross section are the quantities which decide the type of vibrational behavior that a mixed crystal may exhibit.

ACKNOWLEDGMENTS

The author acknowledges the contributions of Tista Basak, M.K. Gupta and S.L. Chaplot (BARC), O. Pages and A. Postnikov (University de Lorraine, France), S.K. Deb (RRCAT), D. Lamago (Laboratoire Leon Brillouin, France), M. d’Astuto (IMPMC, Universite Paris, France) and A. Ivanov (Institut Laue Langevin, France). Part of the work reported here was funded by the Indo-French Center for the Promotion of Advanced Research (IFCPAR) project No. 3204-1.

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REFERENCES

1. J. Gaines et al., Appl. Phys. Lett. 62 (1993) 2462. 2. J. Camacho et al., J. Phys. Cond. Matt. 14 (2002) 739. 3. A. Breidi et al. Phys Rev B 81 (2010) 205213. 4. Chang et al., Adv. Phys. 20 (1971) 359. 5. Vogelgesang et al., J. Raman Spec. 27 (1996) 239. 6. O. Pages et al., Phys. Rev. B 65 (2001) 035213. 7. S.L. Chaplot et al., Eur. J. Mineral. 14 (2002) 291. 8. T. Basak et al., J. Phys. Cond. Matt. 24 (2012) 115401. 9. G.K. Pradhan et al., Jpn. J. Appl. Phys. 50 (2011) 05E02. 10. T. Basak et al., Physica B 407 (2012) 4478. 11. A. Postnikov et al., Phys. Rev. B 71 (2005) 115206.

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Interesting Spectral Evolution In Fe-Based Superconductors

Kalobaran Maiti,*

Department of Condensed Matter Physics and Materials' Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India

Ganesh Adhikary, Nishaina Sahadev, Deep Narayan Biswas, R.Bindu, N. Kumar, C. S. Yadav, A. Thamizhavel, S. K. Dhar and P. L. Paulose

Abstract. Fe-based superconductors are studied extensively during past decade to understand the interplay of superconductivity and magnetism. We studied the electronic structure of some of these fascinating systems exhibiting antiferromagnetic ordering and superconductivity, employing high resolution photoemission spectroscopy. We observed signature of finite hybridization of the electronic states corresponding to the local moment and the conduction electrons. The electronic states near Fermi level exhibit significant pnictogen/chalcogen p character. Signature of Kondo like features are observed near M-point in correlated Fe-compound.

Keywords: Superconductor, iron pnictide, iron chalcogenide, photoemissionPACS: 74.20.Mn, 71.20.-b, 74.70.-b, 75.30.Fv, 79.60.-i

INTRODUCTION

Most of the high temperature superconductors are originated from magnetic parent compounds although magnetism and superconductivity are mutually exclusive phenomena. E.g., superconductivity in cuprates appear from antiferromagnetic ceramic compounds, superconductivity in Fe-based compounds appear from the parent compounds possessing spin density wave ground states. There are differences between the cuprates and Fe-based compounds. The parent compounds of the cuprate superconductor are antiferromagnetic Mott insulators [1] that becomes metallic and the antiferromagnetism disappears with charge carrier doping. Superconductivity emerges onfurther doping with a maximum transition temperature, Tc at about 15% hole-doping. The normal phase in the underdoped regime exhibit pseudogap that vanishes at a characteristic temperature much higher than Tc

The parent compounds in the Fe-based systems are metallic and exhibit spin density wave ground state[3]. The magnetic transition temperature, T

[2].The normal phase in the optimally doped and highlyoverdoped regimes exhibit marginal Fermi liquid and Fermi liquid behavior, respectively.

N gradually decreases with doping/application of pressure.Eventually superconductivity emerges and a finitephase space is observed to have coexistence of antiferromagnetism and superconductivity. These compounds form in varieties of crystal structures -RFeAsO (R = rare earths) forms in ZrCuSiAs

structure, AFe2As2 (A = Ba, Sr, Ca and Eu) inThCr2Si2 structure, MFeAs (M = Li, Na) crystallizes in Cu2

In order to address this issue, we studied some of the Fe-based compounds employing high resolution photoemission spectroscopy - here, we present a brief review of our studies on EuFe

Sb structure and FeSe/Te in �-PbO type structure. Depending on the composition and structure, they have been classified as `1111', `122', `111', `11' families etc. [4] All these materials contain `FeAs' layers sandwiched by spacer materials. `FeAs' layers play the key role in their electronic properties. The pnictogens (As, P etc.) lie above and below the Fe plane (ab-plane). Thus, the hybridization of the Fe 3dstates with the pnictogen p-states involves the z-axis, and pnictogen height (the height of the pnictogen layerfrom the Fe-layers) is an important parameter to derive the non-locality of the conduction electrons. The system earn more local character and become more correlated for larger pnictogen height. Recent studies revealed that the exchange interaction strength, J plays dominant role in their physical properties and hence, these materials are often called as `Hund's metal'. While the magnetism in Fe-based systems is expected, the occurrence of superconductivity is indeed a puzzle.

2As2 and FeTe0.6Se0.4

PREVIOUS WORKS

.

EuFe2As2 forms in the tetragonal structure withspace group I4/mmm and the FeAs-layers are separated by Eu-layers. It shows spin density wave transition at

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 15-18 (2013); doi: 10.1063/1.4790893

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190 K due to Fe-moments and antiferromagnetic transition at 20 K due to Eu-moments. Interestingly, this compound exhibits superconducting phase via chemical substitution at any of the sites [5-6]. Even the parent compound exhibits superconductivity on application of pressure [7]. The antiferromagnetism due to Eu-layers survives within the superconducting phase. Previous ARPES-data [8] on EuFe2As2

FeTe

suggested that the FeAs-layers and Eu-layers aredecoupled indicating no influence of local moments on its superconductivity.

0.6Se0.4 possesses large pnictogen height [9],has no intermediate layer between the `FeSe/Te' layers, and forms in anti-PbO-type crystal structure (space group P4/nmm). The end members, FeTe shows spin density wave (SDW)-type antiferromagnetic transition at 65 K and FeSe is a superconductor below 8 K. Substitution of Te in Se-sites increases Tc with a maximum Tc

EXPERIMENTAL DETAILS

of 15 K for about 60% of Te concentration [10]. Photoemission studies exhibit narrowing of the Fe bandwidth and large mass enhancement due to strong electron correlation - the spectral behavior predicted to be in the Bardeen-Cooper-Schrieffer (BCS)-Bose-Einstein condensate (BEC) crossover regime [11].

Single crystals of EuFe2As2 were grown using Sn-flux as described elsewhere [6]. The sample quality was verified by detailed sample characterization methods such as x-ray diffraction (XRD) pattern and Laue pattern for crystallinity check, energy dispersive analysis of x-rays (EDAX) for composition analysis and finally, x-ray photoemission spectroscopy (XPS).The XRD and Laue patterns were sharp and possess no spurious signal that established good crystallinity of the sample. EDAX and XPS results showed the sample to be stoichiometric and have no impurity that ensured high quality. The highest Tc compound, FeTe0.6Se0.4was prepared in the single crystalline form by the chemical reaction of the elements (Fe of 99.999% purity, Te of 99.99% purity and Se of 99.98% purity) in the stochiometric proportion, inside a sealed quartz tube under vacuum [10]. The charge was heated to 950 oC at the rate of 50 oC / hour, kept for 12 hours, cooled down to 400 oC at the rate of 6 o

The photoemission measurements were carried out using monochromatic photon sources and Gammadata Scienta, R4000 WAL electron analyzer at a base

pressure better than 3x10

C/hour and then the furnace was switched off to cool down to the room temperature. The crystals were highly shiny and grown along the ab plane, and were easy to cleave along this plane. The transport and magnetic measurements exhibit superconducting transition at 15 K.

-11 torr. The temperature variation down to 10 K on the sample was achieved using an open cycle helium cryostat, LT-3M from Advanced Research Systems, USA. The energy resolution was fixed to 2 meV for angle integrated photoemission (AIPES) and 10 meV for angle-resolved photoemission spectroscopy (ARPES) with angle resolution set to 0.3o. The sample was cleaved in a vacuum better than 3x10-11 torr at each temperature just before the measurements. Since the intensity of the He II photon source was relatively weak, several cleaving was required to achieve reasonable signal to noise ratio at each temperature.

RESULTS AND DISCUSSIONS

In Fig. 1, we show the valence band spectra [12] of EuFe2As2

collected at 10 K using Al K�, He II and He I photon energies. All the spectra exhibit two distinct features - one around 1.5 eV binding energy and the other near Fermi level. The relative intensity of the feature changes significantly with the change in probing photon energy. It is well known that the photoemission cross section changes with the change

FIGURE 1 (a) Valence band spectra of EuFe2As2 at AlK�, He II and He I photon energies collected at 10 K. (b)Calculated Fe 3d and As 4p density of states using fullpotential linearized augmented plane wave method(Wien2k software).

16

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in photon energy [13] - the photoemission cross section of Fe 3d and As 4p states is comparable in He I(4.8 and 3.85) and Al K����������and������ photon energies. However, Fe 3d becomes significantly enhanced at He II photon energy compared to As 4pstates (8.75 and 0.29 respectively). On the other hand the atomic cross section of Eu 4f states is 0.75, 3 and 0.017 at He I, He II and Al K� energies respectively.

From the intensities of the peaks at different photon energies, it is clear that the feature at 1.5 eV binding energy appear due to Eu 4f states. Similar intensity of the feature in He I and He II spectra despite significant change in photoemission cross section indicates large covalency between Fe 3d and As 4p states. In order to verify this, we have calculated the density of states using full potential linearized augmented plane wave method (FLAPW) within the local density approximations (LDA) using Wien2k software [14].The partial density of states (PDOS) corresponding to As 4p and Fe 3d states are shown in Fig. 1(b). Clearly,the electronic states close to the Fermi level primarily dominated by the Fe 3d states as predicted in earlier studies with As 4p states appearing around 3 eV binding energies. Thus the signature of large As 4pcontribution in the experimental spectra is in conflict with the calculated results and indicate important role of electron correlation, which is often not treated adequately in such calculations.

Decrease in temperature leads to a significant modification of the spectral density of states near the Fermi level. The spectral density of states can be obtained by symmetrization of the experimental spectra. Thus obtained spectra are shown in Fig. 2. Change in temperature across the SDW transition

leads to a significant change in intensity at the Fermi level in both the cases. Interestingly, a significant dip is observed at 10 K, which is below the antiferromagnetic transition temperature due to Eu moments. This suggests that the electronic states close to the Fermi level responsible for the electronic properties of this system is significantly influenced by the local moments in the Eu layer indicating signature of their active role in the superconductivity of this material.

We now turn to the FeTe0.6Se0.4, which is expected to be a correlated compound among the Fe-based superconductors. Since, this compound has a tendency to have excess Fe/impurities, we show the Al K�spectrum in wide energy range in Fig. 3(a). No signature of impurity was found. The absence of multiple Fe signals in Fe core level spectra indicates

similarities of all the Fe-entities - no interstitial Fe.The valence band exhibit four distinct features marked as A, B, C and D appearing around 0, 2, 4 and 6 eV binding energies. In order to understand the origin of the experimental features, we also show the calculated density of states of the parent compounds FeTe and

FIGURE 2 Temperature evolution of the spectraldensity of states at the Fermi level obtained bysymmetrization of the (a) He II and (b) He I spectra.

FIGURE 3: (a) Wide scan spectra of FeSe0.6Te0.4 at 10 Kobtained using Al Ka photon energy. (b) Valence band spectra of FeSe0.6Te0.4 at 300 K and 10 K exhibitinginteresting spectral evolution. The calculated density ofstates of the parent compounds FeSe and FeTe are alsoshown.

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FeSe. Comparison of the features suggest dominant contribution of Fe 3d states close to the Fermi level. The chalcogen states appear at higher binding energies. Finite intensity of the chalcogen p states in the vicinity of the Fermi level suggest covalency between Fe 3d and chalcogen p states. Interestingly, a decrease in temperature leads to a significant enhancement of the intensity of the feature Aappearing near the Fermi level.

In order to investigate this further, we have collected the data with high energy and angle resolution at 300 K and 10 K using He I photon energy. The spectra collected at the M-point is shown in Fig. 4. The raw data exhibit the crossing of the spectra below the Fermi level indicating a dip at the Fermi level. The spectral density of states are estimated by the division of the resolution broadened Fermi function. We observe signature of a sharp feature above the Fermi level which does not exist at

300 K. The temperature dependence and its appearance just above the Fermi level indicate a Kondo-type excitation present in this system. This is probably the reason of resistivity upturn observed in this system prior to the onset of superconductivity.

CONCLUSIONS

We have studied the electronic structure of EuFe2As2and FeTe0.6Se0.4 using high resolution photoemission spectroscopy. We observed significant role of covalency in these systems. The pnictogen/chalcogen p states appear to play major role in determining the electronic properties of these system. Signature of Kondo type excitation is observed in the electronic structure of the correlated FeTe0.6Se0.4 compound.

ACKNOWLEDGMENTS

The authors, K.M. and N.S. acknowledge financial support from the Department of Science and Technology, Government of India under the `Swarnajayanti Fellowship programme'.

REFERENCES*Corresponding author: [email protected]

1. A. Damascelli, Z. Hussain, and Z.-X. Shen, Rev. Mod. Phys. 75, 473 (2003).

2. T. Timusk and B. Statt, Rep. Prog. Phys. 62, 61 (1999).3. G. R. Stewart, Rev. Mod. Phys. 83, 1589 (2011).4. K. Ishida, Y. Nakai, H. Hosono, J. Phys. Soc. Jpn. 78,

062001 (2009).5. H.S. Jeevan et al. Phys. Rev. B 78, 092406 (2008); ibid.

Phys. Rev. B 83, 054511 (2011).6. N. Kumar et al., Phys. Rev. B 80, 144524 (2009).7. N. Kurita et al. Phys. Rev. B 83, 214513 (2011).8. S. de Jong et al., Europhys. Letts. 89, 27007 (2010).9. K. Kuroki et al. Phys. Rev. B 79, 224511 (2009).10.C. S. Yadav et al, Europhys. Lett. 90 27011 (2010).11.Y. Lubashevsky et al, Nature Phys. (London) 8, 309

(2012).12. G. Adhikary et al. AIP Conf. Proc. 1347, 169-172

(2011).13.K. Maiti and D.D. Sarma, Phys. Rev. B, 58, 9746

(1998).14.P. Blaha, K. Schwarz, G. K. H. Madsen, D. Kvasnicka,

and J. Luitz, WIEN2k, An Augmented Plane Wave +Local Orbitals Program for Calculating Crystal Properties (Karlheinz Schwarz, Techn. UniversitätWien, Austria), 2001. ISBN 3-9501031-1-2.

FIGURE 4: High angle and energy resolved valence band spectra at M-point of FeSe0.6Te0.4 using He I photon energy.The raw data are shown in (a) and the spectral density ofstates obtained by division of resolution broadened Fermifunction is shown in (b).

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The Vortex Explosion Transition

M. N. Kunchur1, M. Liang1, and A. Gurevich2

1Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208, U.S.A. 2Department of Physics, Old Dominion University, Norfolk, Virginia 23529, U.S.A.

Abstract. In type-II superconductors an applied magnetic field B, between the lower and upper critical values, produces a mixed state containing Abrikosov vortices. These vortices contain a quantum of magnetic flux h/2e and consist of a core with depressed order parameter and a pattern of perpetually circulating supercurrents. When B is applied parallel to a thin film, the circulating supercurrents get squeezed by the film surfaces causing the vortex core to become unstable and explode all the way across the film when the thickness d is below the critical value of dc = 4.4ξ ; here ξ is the superconducting coherence length. For temperatures above the explosion condition dc(T) > d, the applied B cannot induce single parallel vortices, however perpendicular vortices can be generated spontaneously by thermal fluctuations. We observe a transition from non-dissipative to dissipative behavior at the explosion condition and find that the dynamics of the spontaneous perpendicular vortices can be tuned by the pairbreaking effect of the applied parallel field.

Keywords: Enter Keywords here. PACS: 74.25.Wx, 74.25.Ha, 74.25.Op, 74.25.Uv

INTRODUCTION

In type-II superconductors, Abrikosov magnetic flux vortices (containing a quantum of magnetic flux h/2e) can arise in two ways: They can be induced by an applied magnetic field or they can be spontaneously generated through thermal fluctuations. In the former case, the magnetic field must lie between the lower critical value (Bc1) and upper critical value (Bc2) and sample dimensions must be adequate to accommodate vortices. In the latter case, vortices can arise within a thin film due to the well known Berezinskii-Kosterlitz-Thouless (BKT) mechanism (unbinding of vortex-antivortex pairs) or through the nucleation of single vortices at the film edge (unbinding from antivortex images) as proposed recently by Gurevich and Vinokur1.

For vortices to exist stably within the sample, the magnetic field must exceed Bc1. For thin films in a parallel magnetic field, Bc1 is boosted with respect to its usual bulk value and was shown by Abrikosov2 to be:

Bc1// = [2�0/�d2] ln (d/�) for d << �� (1)

where �0 = h/2e is the flux quantum, � is the London penetration depth, d is the film thickness, and � is the

coherence length. The second condition for the existence of a single parallel vortex in the middle of the film is whether the thickness exceeds the crticial value: dc = 4.4 �(T). (2) As T increases, dc(T) in increases and at some point exceeds d. The vortex core then explodes3. In this work, we studied the resistive behavior of a molybdenum-germanium thin film in a magnetic field parallel to the film plane and were able to achieve the d < 4.4 �(T) condition for an appreciable temperature range. We saw a change in the transport response close to the predicted vortex explosion transition.

EXPERIMENTAL METHODS

The sample consisted of a film of thickness d=50 nm sputtered onto silicon substrates from a Mo0.79Ge0.21 alloy target. The patterned bridge had dimensions of length l=102 �m and width w=6 �m and were made with photolithography followed by argon-ion milling. The film has the following parameters: transition temperatures TC=5.45 K, normal-state resistances Rn= 540 �, upper-critical-field slope dBc2/dT|Tc= -3.13 T/K, depairing-current

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 19-21 (2013); doi: 10.1063/1.4790894

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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slope dId2/3/dT|Tc= -0.0119 A2/3/K, and the Ginzburg-

Landau parameter = 147. Measurements were conducted in a Cryomech

pulsed-tube closed-cycle refrigerator. Electrical resistivity measurements were made with a standard dc four-probe method for low currents I or with 0.005% duty-cycle 20 �s duration pulses for high I values. Fig. 1 shows the patterned sample and the the orientations of the applied magnetic field and transport current. Further details of the measurement techniques are given in previous review articles4,5 .

FIGURE 1. Patterned sample showing voltage (V-V) and current (I-I) contacts and direction of applied magnetic field (B) and transport current (I).

DATA AND ANALYSIS

There appears to be a separation between a low-B/low-T regime and a high-B/high-T. In the former there is a well defined critical current IC below which there is no observable dissipation and above which there is a jump to the normal state. This IC is very high, only about an order of magnitude below the depairing current Id. Figure 2 shows this measured IC at various B and T values.

In the high-B/high-T regime, there is always resistance even in the limit of vanishing current and the response is Ohmic at low currents, becoming non-linear at high currents. This behavior is illustrated in Figure 3(a). The activated nature of this resistive regime is appartent from the observed Arrhenius temperature dependence (log R 1/T) shown in Figure 3(b).

To better demarcate the separation between the

0 2 40.0

0.3

0.6

0.9

I C (m

A)

B (T)

T = 3.95 K 4.33 K 4.80 K

FIGURE 2. Critical current at various temperatures and magnetic field.

10 100

0.01

0.1

1

0.18 0.19

10

100

(b)

(a)Ohm's law

B= 0.64T 0.75T 0.87T 0.93T

V (m

V)

I (�A)

R (�

)

T-1 (K

-1)

B = 0.1 T B = 1 T

FIGURE 3. (a) Current-voltage curves at T = 5.17 K. At low currents the response is Ohmic (V I). (b) “Log R versus 1/T” plots at I=20 �A where the response is Ohmic (as per panel (a)). The Arrhenius behavior is indicated by the linear decline with 1/T. high-B/high-T resistive regime and the low-B/low-T non-dissipative regime, we measured resistive transitions in various magnetic fields and applied currents as shown in Figure 4. The arrows on the T axis indicate a transition temperature TV at which the R(T) curves at low B converge and plunge to zero. In the limit of the lowest currents and magnetic fields, we observe that TV = 4.7 K. From the calculated coherence length at this temperature and

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Eq. 2, we get 4.4�(T=4.7K) = 52 nm. This agrees well with the nominal film thickness of d = 50 nm.

FIGURE 4. Resistive transitions in various parallel magnetic fields and applied currents. The arrows on the T axis indicate a transition temperature at which the R(T) curves at low B converge and plunge to zero.

Thus there is indeed a marked change in the transport behavior at the predicted vortex explosion transition. What then is the nature of the states above and below TV? One would expect that parallel vortices should be allowed below TV and forbidden above it. We note however that some of the lower applied fields at which TV is observed don’t in fact exceed the lower critical field. From Equation 1, Bc1

// ≈ 0.7 T at T=4.7K, becoming even larger at lower T. Thus the system is in the Meissner state across TV and over most of the region of interest. We believe that the resistive state above TV (where single parallel vortices are forbidden by the explosion condition) arises from thermally activated hopping of short perpendicular vortices nucleated at the edges by thermal fluctuations, as per the mechanism of Gurevich and Vinokur1 mentioned earlier. The allowance of parallel vortices below TV (even though energetically unfavorable when B< Bc1

//) somehow interferes with this edge nucleation process preventing dissipation in that regime.

ACKNOWLEDGMENTS

We gratefully acknowledge Jiong Hua, Zhili Xiao, James M. Knight, and Richard A. Webb. This work was supported by the US Department of Energy through Grant No. DE-FG02-99ER45763.

REFERENCES

1. A. Gurevich and V. M. Vinokur, Phys. Rev. Lett. 100, 227007-227010 (2008).

2. A. A. Abrikosov, Zh. Eksp. Teor. Fiz. 46, 1464-1467 (1964) [Sov. Phys. JETP 19, 988-991 (1964)].

3. K. K. Likharev, Rev. Mod. Phys. 51, 101-159 (1979). 4. M. N. Kunchur, Mod. Phys. Lett. B 9, 399-426 (1995). 5. M. N. Kunchur, J. Phys.: Condens. Matter 16, R1183- R1204 (2004).

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Unidirectional Crystallization of Charged Colloids

Junpei Yamanakaand Akiko Toyotama

Faculty of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe,

Mizuho, Nagoya City, Aichi 467-8603, Japan. E-mail: [email protected]

Abstract. Submicron-sized colloidal particles dispersed in liquid medium self-assemble into ordered “crystal” structures, where the particles are regularly arranged in the body-centered- or face-centered-cubic lattice symmetries. Because of large sizes and long characteristic times of the colloidal particles relative to atoms, the colloidal crystallization has been a useful model to study the phase behavior of atomic systems in general. In addition, since the Bragg wavelengths of the colloidal crystals usually lie in visible light regime, the colloidal crystals have attracted considerable attention as novel photonic materials. Here we report the charge-induced crystallizations, unidirectional crystallizations under gradients of pH and temperature, and gel immobilizations of the charged colloidal crystals.

Keywords:Charged colloids, Crystallization, Photonic Crystals, Crystal Growths PACS: 82.70.Dd, 64.70.D-

INTRODUCTION

Charged colloidal particles dispersed in aqueous media are stabilized due to long-range electrostatic interparticle interaction.At weak interactions the spatial distribution of the colloidal particles is almost random and disordered. With increasing the interaction magnitude, the charged colloids undergo a phase transition to the ordered “crystal” state, where the particles are regularly arranged.1 FIGURE 1 illustrates the crystallization of the charged colloids. The micrographs shown in FIG.1 were taken by using a confocal laser scanning microscope.

Major governing parameters of the interaction magnitude, which is a driving force of the crystallization,are the particle charge number Z, salt concentration Cs, and particle volume fraction �. The interaction is stronger at higher values of Z and �. Salts added to the colloids dissociate into small ions, by which the electrostatic interaction is screened. Therefore the interaction is weaker at higher values of Cs. Thus far, the crystallization of charged colloids has extensively been studied as models to study phase transition in general.2 Furthermore, in recent years, colloidal crystals have attracted considerable attention as photonic crystals,3since their Bragg wavelengths usually lie in the optical regime. Here we report the charge induced crystallization of colloids,4 unidirectional crystallization,5,6 and also gel immobilization of the colloidal crystals. 7

FIGURE 1.An illustration of crystallization (order-disorder phase transition) of charged colloids (left), and confocal laser scanning micrographs (right, particle diameter = 300 nm).

RESULTS AND DISCUSSION

A. Charge Induced Crystallization of Colloidal Silica

We used aqueous dispersions of colloidal silica

(SiO2) particles having the diameter of about 100 nm. The silica particles are slightly charged in their aqueous dispersions due to self-dissociations of silanol groups on their surfaces (�Si–OH ��Si–O– + H+).8 Since the silanols are weak acids, the charge number of the silica particle increases with the addition of a

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 22-25 (2013); doi: 10.1063/1.4790895

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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base, such as sodium hydroxide NaOH(�Si–OH + Na+OH–��Si–O– Na+ + H2O). We found that the silica colloids undergo charge-induced crystallization upon addition of a base under appropriate conditions.FIGURE 2 is the crystallization phase diagram defined by the three experimental parameters(For the charge number, we used the effective value Zedetermined by electrical conductivity measurements). The crystal states were detected by observing Bragg diffractions. The region where Cs is smaller than that at the phase boundary (shown by rectangles) corresponds to the crystal state.

FIGURE 2. A crystallization phase diagram for aqueous dispersion of colloidal silica (the particle diameter = 120 nm) The phase boundary was shown by rectangles. Dashed lines are guides for the eye.

B. Unidirectional Crystallization Due to Base Diffusion

Usually, the maximum size of colloidal crystals

is in the millimeter range. However, larger crystals are sometimes required for material applications. In ordinary crytsalline materials, e.g. semiconductors, large and high quality ctystals have frequently been fabricated by directed crystallization under temperature gradient (Bridman method etc). Similarly, large crystals of charged colloids should be obtained by performing crystal growth under gradients of Z, Cs or �. We have studiedunidirectional crystallization of silica colloidsunder gradient of Z, by using a diffusion of base (pyridine, Py).5FIGURE 3 showsanillustration of experimental setup used. Py molecules are diffused into colloidal silicafrom a reservoir of

FIGURE 3. Illustrations and images for typical crystal growth process of colloidal silica due to diffusion of pyridine.

FIGURE 4. Crystal growth curves for colloidal silica due to diffusion of Py at three values of [Py]0(Py concentration in the reservoir). Solid and dotted curves are theoretical growth curves for salt-free condition and in the presence of 5 �M salt. an aqueous Py solution through a semipermeable membrane (cell size = 1×1×4.5 cm, reservior volume = 500 mL). The photographs on the crystallization process are also shown in FIG.3 (��= 0.034, Py concentration in the reservoir, [Py]0, = 100 mM). Columnar shaped crystals having a few centimeter lengths were formed within one day. FIGURE4shows the observed crystal height, h, plotted against time t. [Py]0values were 100, 10, and 1 mM. The data points in the single growth experiments are represented by the same symbols (circle, triangle, or square). We calculated crystal growth curves based on the diffusion equation, by assuming that the crystallization take place instantaneously, when Py concentration reached to the criticle value for the crystallization (S*). The solid and dotted curves in FIG. 4 are the theoretical growth curves for salt-free conditionand in the presence of 5 �Msodium chloride.The values of S* determined by the phae diagram was 40�M and 60 �M, respectively. The theoretical growth curves agreed well with the observations. This suggests that the

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unidirectional crystal growth process is attributed to a combination of (i) the diffusion of the Py accompanied by a charging reaction of the silica particles and (ii) the charge-induced crystallization of the silica colloids. The crystal size was significantly changed with growth rate. The largest crystals we obtained had a maximum length of a few centimeters and maximum cross-sectional area of 1 � 1 cm.

C. Unidirectional Crystallization under Temperature Gradient

We have also examined the controlled

crystallization under temperature gradient.Generally the temperature is not a very effective parameterfor the interparticleinteractions. However, one can tune the interaction by temperature through temperature dependence of Z, Cs, and��. Wehave already reported that the colloidal silica in the coexistence of Py exhibited crystallization upon elevating temperature.9 This was due to enhanced dissociation of Py (that is, increase in pH) in aqueous solutions,on heating.

Based on this thermally induce crystallization, we have studied the unidirectional crystallization by heating one end of the silica colloids containing Py.6

FIGURE 5(a) shows an illustration of the experimental setup. In FIG 5(b) photographs on typical crystallization process is presented (starting at t = 0; � = 0.05). The present methodenables the fabrication of well-oriented and large (1 mm x 1 cm x 3 cm) single-domain crystals, in a short time (<10 min).Moreover, the crystals have sharp and deep transmission dips aswell as good spatial uniformity in the Bragg wavelength (0.1%).By assuming instantaneous

FIGURE 5. (a) Experimental setup of the thermally induce unidirectional crystallization. (b) Images of crystallization process.

crystallization, wecalculated the crystal length at various t, which showeda closeagreement with the experiments. This suggests thatthe present growth is attributed to a combination of heat conductionand thermally induced crystallization.

Heat conduction is a diffusion of thermal energy, which can be much faster than massdiffusion. Thus, the growth rate of the thermally induced crystallization couldbe much larger than that due to Py diffusion (lessthan a few mm/h). The good uniformity attainedin the present crystallization appeared to rely on its much fastergrowth rate.

D. Gel Immobilization of Colloidal Crystals

The large crystals obtained in the above

mentioned studies may be applicable as photonic materials. However, the colloidal crystals are easily melt by shear, because the crystal structures are formed in liquid media. Gel immobilization of the colloidal crystals has been studied extensively, as it is a considerably important technique for device applications. In many studies, polyacrylamide gels have been utilized to immobilize colloidal crystals. However, they are not suitable for the large crystals obtained in our studies because the acrylamide monomer decomposes in aqueous solution to produce small amounts of ionic impurities, resulting in the melting of the large crystals.However, we were able to immobilize the large crystals by using N-methylolacrylamide as the gel monomer, which could be satisfactorily deionized by using the ion-exchange method.7, 5, 6(b) An image of such a large gelled crystal obtained by using the Py diffuion is shown in FIGURE6. FIGURE 6. An overview of a gel-immobilized colloidal crystal obtained by Py diffusion. We note that the gelled crystals are easily deformed by applying mechanical stress. This deformation causes changes in the Bragg diffraction wavelength of the colloidal crystals fixed in the gel matrix (see FIG.7(a)). That is, the Bragg wavelength

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of the immobilized colloidal crystals are tunable by varying mechanical stress. The relation between the gel thickness (reduced by the initial value) and Bragg wavelength is demonstrated in FIG.7(b). The plots showed good linearity in almost entire visible light wavelength regime.

FIGURE 7. (a)Tunings of Bragg wavelength of a gel-immobilized colloidal crystal by mechanical compression. (b) Bragg wavelength vs. gel thickness y (reduced by a initial value y0) plot for three samples.

CONCLUSIONS

Here we described the crystallization and unidirectional crystal growth of charged colloidal silica. Colloidal crystals with sizes in the cubic-centimeter range were obtained by the base diffusion method. The colloidal crystals having better optical properties were obtained by unidirectional crystallizations under temperature gradient. The colloidal crystals could be immobilized in the polymer hydrogel matrix. We expect that the large gelled crystals obtained here will be useful as photonic materials.

ACKNOWLEDGMENTS

The present study was supported in part by a Grant-in-Aid of the Ministry of Education, Science and Culture, Japan. A part of this study was performed as the “Three-Dimensional Photonic-Crystal (3DPC) Project” of the Japan Aerospace Exploration Agency(JAXA).

REFERENCES

1. For review articles and textbooks, (a) Pieranski, P. Contemp. Phys.24, 25(1983). (b) Russel, W.B.; Saville, D.A.; Schowalter, W.R. Colloidal Dispersions; Cambridge University Press: New York, 1989. (c) Sood, A.K. Solid State Phys.; Ehrenreich, H. and Turnbull, D., eds.; Academic Press: New York, 1991. (d) Arora, A.K.; Tata, B.V.R., eds.; Ordering and Phase Transition in Charged Colloids; VCH: New York, 1996. (e) Ise, N.; Sogami, I.S. Structure Formation in Solution; Springer: Berlin, 2005.

2. (a) Anderson,V.J.; Lekkerkerker, H.N.W. Nature, 416, 811 (2002). (b) Yethiraj, A.; van Blaaderen, A. Nature, 421, 513 (2003).

3. Joannopoulos, J.; Meade, R.; Winn, J. Photonic Crystals; Princeton University Press: 1995.

4.(a) Yamanaka, J.; Koga, T.; Ise, N.; Hashimoto, T. Phys. Rev. E, 53, R4314 (1996). (b) Yamanaka, J.; Yoshida, H.; Koga, T.; Ise, N.; Hashimoto, T. Phys. Rev. Lett., 80, 5806 (1998). (c) Yoshida, H.; Yamanaka, J.; Koga, T.; Koga, T.; Ise, N.; Hashimoto, T. Langmuir, 15, 2684 (1999).

5. Yamanaka, J.; Murai, M.; Iwayama, Y.; Yonese, M.; Ito, K.; Sawada, T. J. Am. Chem. Soc., 126, 7156 (2004). M.Murai et al., Langmuir23, 7510 (2007); Wakabayashi et al., Langmuir, 22, 7936 (2006).

6. A.Toyotama, et al., J. Am. Chem. Soc.129, 3044 (2007); A.Toyotama, et al., Langmuir25, 589 (2009).

7. Iwayama, Y.; Yamanaka, J.; Takiguchi, Y.; Takasaka, M.; Ito, K.; Shinohara, T.; Sawada, T.; Yonese, M. Langmuir, 19, 977 (2003).

8. Iler, R.K. The Chemistry of Silica; Wiley: NY, 1979. 9. Yamanaka, J.; Koga, T.; Yoshida, H.; Ise, N.; Hashimoto,

T. Slow Dynamics in Complex Systems; Tokuyama, M., Oppenheim, I., Eds.;Woodbury: New York; 1998; p 144.

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Magnetic Compton Scattering: A Reliable Probe to Investigate Magnetic Properties

B. L. Ahuja

Department of Physics, University College of Science, M. L. Sukhadia University, Udaipur-313001, Rajasthan, India

Email: [email protected]

Abstract. Magnetic Compton scattering (MCS) is an ideal technique for the study of magnetic properties of ferro/ferrimagnetic materials because this method reveals the spin-polarized electron momentum density and yields the absolute and site dependent spin moments. The quantity measured in the MCS, so called magnetic Compton profile, is defined as the difference in the one-dimensional projection of the spin-polarized electron momentum density for majority and minority spin bands. In MCS, the Doppler broadening of the scattered radiation provides information on the correlation between the spin moment and the spin-polarized electron states of the valence electrons. It can also distinguish the spin polarization of itinerant electrons, because their momentum is narrow around the center of the profile. In this paper, temperature and field dependent spin momentum densities in Zn doped Ni ferrite namely, Ni1-

xZnxFe2O4 (x = 0.0, 0.1, 0.2), hole doped manganites like La0.7Ca0.3Mn1-xAlxO3 (x = 0, 0.02 and 0.06) and half Heusler alloys Cu1-xNixMnSb (x = 0.17, 0.22) are reviewed. The decomposition of profiles in terms of site specific magnetic moments and their role in the formation of total spin moment is also discussed.

Keywords: X-ray scattering, Ferrites, Manganites, Spin-orbit coupling, Ferromagnetic materials, Local magnetic moment PACS: 78.70.Ck, 75.50.Gg, 75.47.Lx, 71.70.Ej, 75.50.Cc, 75.20.Hr

INTRODUCTION

Compton scattering (CS) is an ideal methodology to study the electronic and magnetic properties of a variety of materials [1, 2]. In charge or say normal CS, the charge of the electron interacts with the electric field of incident electromagnetic radiation while the magnetic Compton scattering (MCS) is due to interaction of magnetic field of incident electromagnetic radiation with the magnetic moment of the electron. In Fig. 1, a schematic diagram for MCS is shown. The double differential scattering cross-section (DDSC) of unpaired (magnetic) electrons is directly related to the magnetic Compton profile (MCP), Jmag(pz), of the specimen under study.

Mathematically, DDSC can be defined as, � � (1) .)(pJ)S(Pcos1g

EE

2r

dEd�d

zmagc1

220

mag2

2

������

�� ��

��

In Eq. (1), ,mcE

g 21 Pc is the degree of circular

polarization of the incident radiations and r0 is the classical electron radius. E1(E2) is the energy of incident (scattered) photon and � is the scattering

angle. In case of Fig. 1, the S(�) which is known as geometrical factor is given as )2(�)cos(

EEcos�cos�̂k̂

EEcosk̂�̂)(S

1

22

1

21 ��

����� ��

��� �

where �̂ corresponds to magnetic field direction,

1k̂ and 2k̂ are the unit vectors along the incident and scattered wave vectors (Fig. 1). � is the angle between the sample and the wave vector of incident radiation. Theoretically, Jmag(pz) is defined as the one dimensional projection of spin polarized electron momentum distribution,

Jmag(pz) = J�(pz) -J�(pz)

( ) ( ) , (3)p px yp p x y� � dp dp

� �� � �� �� �

where ��(p) and ��(p) are the electron momentum densities of majority and minority spin bands, respectively. An integration of MCP follows the following normalization conditions,

mag spin( )d . (4)z zJ p p μ�

��

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 26-29 (2013); doi: 10.1063/1.4790896

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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FIGURE 1: Schematic of magnetic Compton scattering. The specimen is kept under the reversing magnetic field B. k1 (k2) and E1(E2) are the wave vectors and energies of the incident (scattered) X-rays, respectively. k (=k2-k1) is scattering vector and � is scattering angle.

Therefore, the MCP is sensitive to spin moment of the ferro- or ferri-magnetic materials. To deduce MCP, one requires circularly polarized radiations and ferro- or ferri-magnetic specimen kept under the influence of external magnetic field.

EXPERIMENTAL SET-UP AND DATA ANALYSIS

A MCS set-up as available at beam line BL08W at SPring8 (Super Photon Ring-8GeV), Japan [3, 4] is shown in Fig. 2.

In the set-up shown in Fig. 2, the circularly

polarized X-rays emitted from an elliptical multipole wiggler (with wiggler gap 25.5 mm) are monochromatized using a bent Si (620) asymmetric Johann-type monochromator. The energy of incident

X-rays is mainly kept near 180 keV. The degree of circular polarization (Pc) is about 0.6. The beam size at the sample position can be varied between 1.5 mm (h) x 1.5 mm (w). A superconducting magnet which can produce the field up to 3T and a minimum polarity switching time of one second is used to magnetize the sample. To separate out the spin dependent (spin-up and spin-down) electron momentum densities of the sample, the magnetic field on the sample is applied in the sequence ��������……., where � and � represent the relative directions of the magnetic field and the k (� being parallel and � being antiparallel to k). Currently, ten-element Ge detection system is used to detect the scattered radiations at an angle of 178º. The resolution (Gaussian full width at half maximum) of the Compton spectrometer is 0.40 a.u.

The spin moment of the sample (�2) is obtained from the percentage magnetic effect R and a reference sample (mostly Fe) of spin moment �1. Mathematically,

)5(.μNN

RR

μ 11

2

1

22

R2 and R1 are the magnetic effects of the unknown and reference samples, respectively. N2(1) are the total number of electrons taking part in the CS of unknown (reference) sample. The magnetic effect R which is ratio of charge to magnetic signal is defined as � �

� �� � � �

� � � �

c

2 2l

cos 1 cos(6)

1 cos sin 1 cos

1 2

1 2

k k.

k ks

I I P FR

NI I Pmc

� �

� �

� � � � � �

��� �� �� � �

Fs and N correspond to number of unpaired electrons (in �B per formula unit) and total number of electrons in the sample, respectively.

MCP STUDIES OF SOME COMPOUNDS

(1) Ni-Zn Ferrite

Ahuja et al. [5] have reported the MCP of Ni1-

xZnxFe2O4 (x=0.0, 0.1 and 0.2) to evaluate the effect of Zn doping on the spin and orbital magnetic moments of NiFe2O4. In Figs. 3 (a-b), the MCP of Ni1-xZnxFe2O4 (x=0.0, 0.1 and 0.2) at 8 and 300 K temperatures under 2.5 T field are shown. The MCPs are decomposed into the profiles of Ni, Fe and diffuse components (as shown in the inset of Fig. 3a), to find their contribution to total spin moment. The total spin moment (at 8 K) of Ni1-xZnxFe2O4 is found to be 1.91, 2.72 and 3.48 �B for x = 0.0, 0.1 and 0.2, respectively. The variation in the site specific spin moments of Fe and Ni with varying concentration of Zn is shown in Fig. 4.

FIGURE 2: Sketch of magnetic Compton spectrometer available at SPring8, Japan. For details, please see Refs. [3, 4] and www.spring8.or.jp.

To magnet power supply

Liquid He condenser

Specimen SR 10-elements

Superconducting magnet

Refrigerator (sample cooling)

Ge-SSD

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FIGURE 3: MCP of Ni1-xZnxFe2O4 (x =0.0, 0.1, 0.2) at (a) 8 K and (b) 300 K. In the inset the MCP (at 8 K) decomposed into the constituent profiles along with the best fitted profile is shown. Experimental errors are within the size of symbols used.

0.00

0.08

0.16

0.24

0.32

0.40

0.48

0.56

0.64

0 2 4 6 8 100.0

0.1

0.2

0.3

J mag(p

z)(� B/a

.u.)

pz(a.u.)

NiFe2O48 K, 2.5 T

Ni Fe-Exp Diffuse Fitted Expt.

(a)

8K x=0.0 x=0.1 x=0.2

0.00

0.08

0.16

0.24

0.32

0.40

0.48

J mag

(pz) (

� B/a.u

.)

pz(a.u.)

(b)

300 K x=0.0 x=0.1 x=0.2

FIGURE 4: Magnetic moments at Ni and Fe sites along with diffuse (itinerant) contribution for different concentrations of Zn in Ni-Zn ferrites.

0.00 0.05 0.10 0.15 0.20

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

300 K8 K

300 K

8 K

300 K

8 K

Mag

netic

mom

ent (

� �/f.

u.)

Zn - concentration

Ni Fe Diffuse

The total and site specific spin moments deduced

from the present MCP measurements are in tune with the reported results [6]. To find the orbital moment in Ni-Zn ferrites, the authors [5] have compared their MCP data with the magnetization data. At x=0, orbital magnetic moment was found to be about 0.25 ± 0.03 μB/f.u. It reduces to 0.15 (0.09) ± 0.03 μB/f.u. for x = 0.1 (0.2) which is in contrast to the corresponding total spin moments. A decrease in ratio of orbital to spin moments in Ni rich ferrites is understandable on the basis of spin-orbit coupling and crystal field interactions.

(2) Al doped La0.7Ca0.3MnO3

Spin dependent momentum densities of La0.7Ca0.3Mn1�xAlxO3 (x = 0 and 0.02) measured at different temperatures [7] using MCS technique at SPring-8 are shown in Fig, 5. From Fig. 5, a decrease in the spin moment of La0.7Ca0.3MnO3 with increase in temperature as well as Al concentration is quite evident. The decomposition of MCPs into its constituent (Mn and diffuse) profiles shows a major role of Mn ions in building up the total spin moment. A negative contribution of diffuse electrons leads to volcano type structures in these profiles. The magnetic moment of Mn ions at 6 K reduces from 4.29 �B/f.u. to 3.95 �B/f.u. with the doping of Al at Mn site. The MCP data when compared with the magnetization data (which includes spin+orbital moment) determines quantitatively the effect of Al doping on the orbital magnetic moment of La0.7Ca0.3MnO3. In case of undoped sample, negative orbital moment (-0.29 ± 0.03 �B/f.u.) is observed while the doping of Al at Mn site reduces the orbital moment almost to zero. This behavior is explained by considering a model which involves Mn3+/Mn4+ ratio [7].

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FIGURE 5: Magnetic Compton profiles of La0.7Ca0.3Mn1-

xAlxO3 (x = 0.0, 0.02) at different temperatures and 2.5 T magnetic field. The area under the curve corresponds to total spin moments. Statistical errors are within the size of the symbols.

-10 -8 -6 -4 -2 0 2 4 6 8 10-0.10.00.10.20.30.40.50.6

(x=0.02)

J mag

(pz)(�

B/a.u

.)

pz(a.u.)

6 K 100 K 200 K 300 K

0.00

0.15

0.30

0.45

0.60

(x=0.00)

0.17 0.18 0.19 0.20 0.21 0.220.00.51.01.52.02.53.03.54.0 Cu1-xNixMnSb

8K and 2.5T

Mag

netic

mom

ent (

� B/f.u.

)

Ni doping (x)

Mn Ni Diffuse Total

FIGURE 6: Total and site specific spin moments in Cu1-

xNixMnSb (x=0.17, 0.22) obtained from the line shape analysis of MCPs at 8 K. Errors in the magnetic moments are ± 0.03 �B/f.u.

(3) Cu1-xNixMnSb (x = 0.17 and 0.22)

Using MCS technique, the effect of Ni doping on the magnetic moment of antiferromagnetic CuMnSb half Heusler alloy is reported by Ahuja et al. [8]. The MCPs of Cu1-xNixMnSb (x = 0.17 and 0 .22) have been measured at different temperatures and a fixed magnetic field of 2.5 T. From the MCP and magnetization data, it is seen that the magnetic moment increases with increase in Ni concentration. The splitting of MCP into its constituent profiles shows an increase in magnetic moment which is due to rise in local spin moment on Mn site. Individual spin moments of Ni, Mn and diffuse electrons along with the total spin moment for Cu1-xNixMnSb (x = 0.17 and 0 .22) derived from the Compton line shape analysis of MCPs (at 8 K) are shown in Fig. 6. Orbital magnetic moment in Cu1-xNixMnSb (x = 0.17 and 0 .22) (magnetization data – MCP data) is found to negligible [8].

ACKNOWLEDGMENTS

The author is grateful to the authorities of SPring8, Japan for beam time. Dr. Y. Sakurai and Dr. M. Itou are thanked for discussion. Author thanks DST, DRDO, UGC and CSIR, New Delhi for financial support at different stages.

REFERENCES

1. M. J. Cooper, P. E. Mijnarends, N. Shiotani, N. Sakai and A. Bansil, X-ray Compton Scattering, Oxford Science Publications, New York, 2004.

2. B. L. Ahuja (Ed.), Recent Trends in Radiation Physics Research, Himanshu Publications, New Delhi, 2010.

3. Y. Kakutani, Y. Kubo, A. Koizumi, N. Sakai, B. L. Ahuja and B. K. Sharma, J. Phys. Soc. Jpn. 72, 599-606

(2003). 4. B. L. Ahuja, V. Sharma and Y. Sakurai, Adv. Materials

Res. 52, 145-154 (2008). 5. B. L. Ahuja, H. S. Mund, S. Tiwari, J. Sahariya, A.

Dashora, M. Itou and Y. Sakurai, Appl. Phys. Lett. 100, 132410-1–4 (2012).

6. X. F. Zhu and L. F. Chen, J. Mag. Mag. Mater. 23, 3138-3142 (2011).

7. B. L. Ahuja, S. Tiwari, A. Dashora, H. S. Mund, J. Sahariya, D. M. Phase, R. J. Choudhary, A. Banerjee, M. Itou and Y. Sakurai, Appl. Phys. Lett. 99, 062512-1–3 (2011).

8. B. L. Ahuja, A. Dashora, S. Tiwari, H. S. Mund, M. Halder, S. M. Yusuf, M. Itou and Y. Sakurai, J. Appl. Phys. 111, 033914-1–5 (2012).

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Development of magnetoresistive thin film sensor for magnetic field sensing applications

P. Chowdhury1*

1Surface Engineering Division, National Aerospace Laboratories, Bengaluru-560017 *[email protected]

Abstract. Recently, nano-dimensional magnetic thin film and multilayer structures have attracted a great deal of interest due to the possibility of unique and desirable magnetic properties. Our research into magnetic thin films is primarily focused on the growth and properties of such structures on Si to develop the magnetic sensors for field sensing applications. Thin films of permalloy (Ni81Fe19 ) were deposited on silicon substrates using Ultra High vacuum (UHV) sputtering system ( ~ 5 x 10-9 mbar). To achieve the negligible hysteresis and high thermal stability of these films, the magnetic and structural properties were optimized by (1) varying thicknesses of magnetic films, and (2) post annealing at various temperatures. Optimized films were then patterned to study the device output characteristics to know about their sensitivity and we achieve the sensitive of the order 45 µV/G/V which is equivalent to any commercially available magnetic sensors. These anisotropic magnetoresistive (AMR) based sensors are very useful for further development of navigation compass to use in strategic sectors for the self reliance of our country.

Keywords: AMR, hysteresis, NiFe. PACS: 75.30.Gw;75.70.-i

INTRODUCTION

Thin film magnetoresistive (MR) sensors are widely used in various applications and have a significant impact over the past fifty years in many different key technological areas due to higher sensitivity, cost effective and small in size. MR sensors are usually divided into two categories based on Anisotropic Magnetoresistive (AMR) and Giant Magnetoresistive (GMR) sensors. This classification results from the different mechanisms and features of these effects. In this report, we have optimized the process parameters for the growth of magnetic thin films based on AMR properties and also fabricated devices using these films.

EXPERIMENT

Highly pure ferromagnetic magnetic thin films of Ni81Fe19 (i.e., permalloy) have been deposited on the SiO2/Si substrates (dimensions: 20 mm×20 mm), while the tantalum (Ta) was used as buffer and cap layers. To get the high purity permalloy thin films, the depositions of these films were carried out using a Ultra High Vacuum (UHV) sputtering system at a base pressure of 10-9 mbar. The structural characterization of these coatings was carried out by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM), while the magnetic characterization was carried out by

magnetotransport system and Vibrating Sample Magnetometer (VSM). Effect of in-situ annealing temperature in the range of 150 to 500 oC was also studied.

Results and Discussion

40 42 44 46 48 50

500oC

470oC

350oC

250oC

150oC

2� (deg.)

Inten

sity (

a.u.)

Unknown Alloy peak

NiFe (111)

420oC

FIGURE 1. Effect of heat treatment in vacuum on the X-ray

diffraction peak position of NiFe (111) reflection planes.

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 30-33 (2013); doi: 10.1063/1.4790897

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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Fig. 1 shows the XRD pattern of the films with structure Ta(10nm)/ Ni81Fe19 (50 nm) /Ta (10nm)/Si annealed in vacuum at temperature from 150-500oC. The main peak observed in XRD data was at 2θ = 43.89o. This peak correspond to (111) reflection plane of the Face Centered Cubic (fcc) crystalline structures of the permalloy thin film. For the films heat treated at temperatures above 350 oC, (111) peak was shifted slightly at higher 2�. Furthermore, at 500 oC, an extra unknown peak was observed. Fig. 2 shows the variation of the grain size of the films (i.e. calculated using Debye Scherre formula) with respect to the annealing temperatures. Up to 420 oC, increase in the grain size from 15 nm to 25 nm was observed, while from 470 to 500 oC, a sharp decrease in the grain size (i.e., 23.31 to 14.76 nm) was observed.

100 200 300 400 50010

15

20

25

30

Gra

in si

ze (n

m)

Temp (oC)

FIGURE 2. Variation of NiFe garin size with temperature

FIGURE 3. plane-view micrographs of the films vacuum annealed at 150 and 470oC, respectively (a-b), corresponding cross-section micrographs (c-d) and their selective area diffraction micrographs

Transmission electron microscopy was performed

for the micro-structural studies of the Ta/Ni81Fe19/Ta/Si thin films vacuum annealed at 150 and 470 oC, respectively. Figs. 3 (a-d) show the 2-dimentional plane- view micrographs, the bright field cross-sectional transmission electron microscopy

(XTEM) micrographs and the selected area diffraction micrograph (SED) of sample annealed at 150 and 470 oC in vacuum for 1 hour.

From the plane-view micrograph as shown in Fig.

3(a), it is confirmed that the lateral grain size of the NiFe film annealed at 150 oC was approximately 15-17 nm. Increase in grain size to 23 nm was further observed by annealing at 470 oC. From the XTEM micrograph, the thickness of the Ta as a buffer layer (1) and cap layer (3) was approximately 10 nm, while the thickness of the NiFe main layer (2) was 50 nm. The SED ring pattern confirms the structure of NiFe and is similar to that observed using X-ray diffraction.

-20 -10 0 10 20

0.0

0.5

1.0

1.5

2.0

2.5

3.0(a)

AM

R (%

)

Field (G)

30 oC 150 oC 200 oC 250 oC 350 oC

-20 -10 0 10 20

0.0

0.5

1.0

1.5

2.0

2.5(b)

AM

R (

%)

Field (G)

420 oC 450 oC 470 oC

0 100 200 300 400 500

0.0

0.5

1.0

1.5

2.0

2.5

3.0

AM

R %

Temperature (Celsius)

(c)

FIGURE 3. (a-b) effect of vacuum annealing on the magnetoresistance behavior of the Ta/NiFe/Ta thin film; (c) Variation of AMR ratio with annealing temperature.

Fig. 3(a-b) shows the AMR curves of Ta/NiFe/Ta films annealed in vacuum for 1 hour at different temperatures. It is confirmed that AMR value increases significantly with increasing the temperature up to 200oC and a maximum value of 2.53% was achieved as shown in Fig.3 (c). Above 200oC, from 250 to 470 oC as shown in these figures, decrease in the AMR values was observed and minimum value was 0.6% for film annealed at 470 oC. As shown in Fig..3 (a), for films annealed at temperatures from 150 to 350 oC, the AMR responses show nearly reversible parabolic behavior which indicates the coherent spin rotation as observed in nano-wires [1]. Furthermore, in Fig. 3(b), films prepared above 350 oC, all the AMR curves show hysteretic behavior with two sharp peaks,

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which is a typical characteristics of multidomain behavior and consistent with anisotropic magnetoresistance effect [2]. The variation of AMR with annealing temperature shown in Fig. 3(c), which shows that AMR disappears at annealing temperature � 500 oC .

-20 -10 0 10 20-300

-150

0

150

300

-20 -10 0 10 20

-800

-400

0

400

800

-20 -10 0 10 20-700

-350

0

350

700

-20 -10 0 10 20-800

-400

0

400

800

-20 -10 0 10 20-800

-400

0

400

800

-20 -10 0 10 20-800

-400

0

400

800

(d)(c)

(b)

150 oC

250 oC

Field (G)

470 oC

M

agne

tic M

omen

t (�

emu)

200 oC

(f)(e)

350 oC

T = 30 oC

(a)

FIGURE 4. (a-f) effect of vacuum annealing on the M(H) curves of the Ta/NiFe/Ta thin film.

The measured M(H) curve for the as deposited film

(at 30 oC) and the films heat treated in vacuum at 150, 200, 250, 350 and 470 oC are shown in the Fig. 4(a-f), respectively. Magnetization measurements were performed at room temperature using the vibrato sample measurement system (VSM). The M(H) curve showed the canted shape for the as deposited film as shown in Fig. 4(a), which changes into rectangular shape for the films heat treated up to 200 oC as shown in Figs. 4(b-c). While for the films heat treated from 250 to 470 oC, shows the canted shapes. The canted shaped M(H) curves are attributed due to strip domain structures which are composed of many fine magnetic domain structures [3]. However, the rectangular shaped M(H) curves observed at 150 and 200 oC confirmed the formation of single domain structures in the thin films, which are generally observed in thinner films[3] and nanowires [1] .

-800 -400 0 400 800-80

-40

0

40

80

O

utpu

t vol

tage

(mV

)

Simulated curve

Magnetic field, Hx (G)

Experimental curve

FIGURE 5. (a) sensor fabricated on a silicon substrate and externally biased by two hard magnets; (b) experimental curve along with the simulated curve.

The developed Ni81Fe19 thin film (thickness =

50nm) having Ta as a buffer layer (thickness = 10nm) was used for the AMR sensor development. Four quasi linear AMR sensors in the form of Wheatstone bridge circuit configuration were fabricated on silicon substrate as shown in Fig. 5(a). For the higher sensitivity and less power consumption in the sensor, each sensor array was patterned in the meander type shape containing 25 multi current paths. To achieve the quasi linear characteristics, each sensor array was patterned out at an angle of ± 45o. But in this case, shape anisotropy is an important parameter, due to which the resultant sensitivity of the sensor may reduce.

As shown in Fig. 5 (a), the sensor paths are inclined at an angle, �� = 45o with respect to the anisotropy axis and this configuration can result as a different resultant anisotropy axis which inclines at an angle � instead of �� . Due to this anisotropy axis deviation by an angle of ∆� = (�� − �), the quasi linear transfer output for this type of AMR sensor geometry can be diminished by a factor of sin 2�� cos 2∆� and the resultant quasi linear output ( for Hx < 0.5 Hk ) for the design as shown in Fig. 5 (a) can be written as:

���� = 2�∆ sin 2�� cos 2∆�1

�� +� cos ∆���

This equation gives the linear output transfer

characteristic and the corresponding sensitivity of the sensor is given as,

� =����

��

MATLAB code for the simple patterned AMR

sensor was generated successfully for the output transfer characteristic equation and the simulation was performed for the optimized sensor parameters, which along with the simulated output results are given below as follows:

(a)

(b)

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Constant parameters: [1] Material constants:

Resistivity of the Permalloy thin film, ρ = 220×10-9

Ωm Maximum resistivity change, ∆/ = 2.5% Magnetization saturation, MS = 24 Gauss Material Anisotropy field, Hko ≈ 20 Gauss Thickness of the Permalloy thin film = 60 nm

[2] Sensor design parameters: Total length of the current path strip in the AMR sensor, L = 1000 µm; Width of the AMR sensor current path strip, w = 20 µm Gap between two current paths, p = 20 µm Total area of the sensor, A = 1 mm2 Total number of current paths, N = 25 Total resistance of the sensor in the bridge circuit = 4.67 kΩ Current density feed to the bridge circuit, J = 1.1157×109 A/m2 (for I = 1.1157 mA) Applied measuring field, HX = -1000 to +1000 Gauss

[3]MATLAB simulated Output values of the AMR sensor:

Value of total anisotropy field, Hk = Hko + Hd + HBo = 1020 Gauss Operating field range, HX = -1000 to +1000 Gauss Sensitivity, S = -56.1 to 56.1 mV/V/Gauss Maximum operating voltage = 6.259 V

Hence for the optimized sensor parameters, the sensor was. 5(a). For the fabricated sensor, prior to find out the quasi linear transfer characteristic, the experimental characterization was performed. To stabilize the sensor (so that to achieve a very low hysteresis, high linearity and high sensitivity), two hard magnets having opposites magnetic poles were fixed nearby the main sensor as shown in Fig. 5(a). The optimized position of both the magnets was 1 cm (i.e., the distance between the centers of the magnet and sensor). Fig. 5 (b) shows the experimental output

voltage along with the simulated output for the developed AMR sensor. Both the curves show a good agreement at lower fields, however it shows a deviation at higher fields.

In conclusion, we have deposited Permalloy thin

films on Si/SiO2 substrates and both the structural and magnetic properties were investigated as a function of annealing temperature. It was observed that the films annealed in the temperatures ranges from 150 to 250 oC were shown highest AMR percentage ( 2.53 %) with single domain characteristics and very useful for the development of AMR based magnetic field sensing devices. Magnetoresistive sensor with Wheatstone bridge configuration are fabricated and the linear output characteristics was found to match qualitatively with simulated data.

ACKNOWLEDGMENTS

Authors would like to thank the Director, NAL for supporting this activity. Authors are grateful for the financial support by Department of Science and Technology (DST) and National Program on Micro and Smart Structures (NPMASS).

REFERENCES

1. S. Goolaup, A.O. Adeyeye, N. Singh, Thin Solid Films, 505 (2006) 29

2. D. Tripathy, A. O. Adeyeye, Phys. Rev. B 79 (2009) 064413.

3. E. Spada, G. Pereira, E. Jasinski, A. da Rocha, O. Schilling, M. Sartorelli, J. Magn. Magn. Mater. 320 (2008) e253.

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Core/ Shell Nano-Structuring of Metal Oxide Semiconductors and their Photocatalytic studies

S. Balakumar* and R. Ajay Rakkesh

National Centre for Nanoscience and Nanotechnology University of Madras, Guindy Campus, Chennai – 600 025

*e-mail: [email protected] Abstract. Core/Shell Nanostructures of Metal Oxide Semiconductors (MOS) have attracted much attention because of their most fascinating tunable applications. These core shell morphologies can be easily engineered to enhance the unique properties of the metal-oxide nanostructures, which make them suitable as photocatalyst due to their high catalytic activity, substantial stability, and brilliant perspective in applications. This paper provides an overview on our work on the synthesis of some interesting core/ shell nanostructures of MOS such as ZnO-TiO2, ZnO-MoO3, and V2O5-TiO2 using a low temperature wet chemical route and hydrothermal techniques and their photocatalytic properties from the aspects of different shell materials and shell thicknesses. The effect of process parameters such as pH, temperature, and ratio of core and shell materials, was systematically studied. Here the evidence for the core shell formation with different shell thicknesses came from the X-ray diffraction peak intensities. The shell thickness variation was also confirmed by Transmission Electron Microscopic studies. Effect of shell thickness on optical band gap of the core shell fabricated was also investigated using DRS UV-Visible spectroscopy. A comprehensive study was carried out for the photocatalytic efficiency of core shell nanostructures by evaluating the photo-degradation of Acridine Orange (AO) dye in aqueous solution under visible and solar light irradiations. These results offered simple approaches to the nanoscale engineering and synthesis of MOS hybrid systems to serve as better photocatalytic materials.

Keywords: Core/shell, Metal Oxide, shell thickness, photocatalytic efficiency PACS: 7

1. INTRODUCTION: Developing unique functional materials and devices with controlled features on the nanoscale is at the core of R & D innovation. Core-shell nanostructures are such an important group of nanomaterials. These systems have drawn huge attention owing to those distinctive structural features that consist of three or zero dimensional inner core and an external two dimensional shell of different chemical composition or materials with different properties. In recent years, core shell engineering allows the possibility to create multifunctional nanomaterials with enhanced properties for wide range of applications including environmental clean, magnetic, electronic, and medical applications [1]. One of such families is the metal oxide core shell multifunctional nanomaterials having wide range of applications as mentioned above due to their significant improved properties and bio-compatibility. In order to fabricate such core–shell nanostructures, it is necessary to develop the synthesis methods of individual materials as well as to identify the strategies to combine them and evaluate the effect of the morphology, size variation, and their subsequent effects on the functional properties of nanomaterials fabricated[2].

Since a photocatalytic process is based on the generation of electron/hole pairs by means of band-gap radiation, the coupling of different semiconductor oxides seems useful to achieve a more efficient electron/hole pair separation under irradiation. Thus, it is possible to enhance the activity of a ZnO photocatalyst by means of TiO2 or MoO3 coupling [3]. Therefore, it is highly desirable to synthesize ZnO/TiO2 and ZnO-MoO3 core shell nanoparticles with a high photocatalytic activity. Similarly, it is also possible to enhance the catalytic activity of V2O5 by adding a TiO2 shell. In this talk, we present the preparation of some metal oxide core shell nanomaterials such as ZnO-TiO2, ZnO-MoO3 and V2O5-TiO2 by wet chemical and hydrothermal techniques. Detailed structural and morphological and optical characterizations were reported here. The variation in the photocatalytic properties of the fabricated core shell systems were also investigated by photocatalytic degradation of Acridine Orange (AO) under UV/solar irritations and the results are presented along with detailed discussions.

2. EXPERIMENTAL DETAILS:

Nanomaterials of ZnO, TiO2, V2O5 and MoO3 were synthesized using wet chemical routes. Based on the

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 34-37 (2013); doi: 10.1063/1.4790898

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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required core size, the preparation temperature (?) was chosen. The preparation details for the individual NPs and core shell are given below MOS Core shell Synthesis: 1. Low temperature synthesis of Zinc Oxide nanoparticles In a typical experiment, 1.0 M of Zinc acetate [Zn(CH3COO)2.2H2O] was dissolved in double-distilled water (200 mL) at ~5 °C and stirred for 30 minute. 1.5 M of Oxalic acid (H2C2O4.2H2O) was dissolved in double-distilled water (200 mL) separately at ~ 5 °C and then it was slowly added to the cold solution of Zinc acetate. Further, the mixture was stirred for 2 h at low temperature and it gradually turned into a white precipitate. The precipitate was then filtered and washed with ethanol and allowed to dry at 80 °C for 2 h, resulting in Zinc oxalate formation. The Zinc oxalate was further calcined at 400 °C for 2 h to form pure ZnO powder. 2. Synthesis of MoO3 nanomaterials For the synthesis of MoO3 nanoparticles, 1.0 M of Ammonium heptamolybdate was dissolved in 4 mL of ethanol and 50 mL of distilled water under constant stirring. The clear solution was transferred in a Teflon lined autoclave and maintained at 180°C for 8 h to obtain a viscous solution of MoO3 nanoparticles. 3. Synthesis of the TiO2 nanogel In a typical experiment, 2.0 M (100 mL) of Titanium tetra-isopropoxide (TTIP) was used as a metal precursor and glacial acetic acid (10 mL) as a solvent. Both the chemicals were mixed and stirred for 2 h and then ultrasonicated for 30 min until a uniform TiO2 nanogel were formed. 4. Fabrication of ZnO/TiO2 core/shell nanostructures ZnO nanoparticles were dispersed in 100 mL of distilled water by ultrasonication. The shell material was added drop-wise on the above synthesized ZnO dispersion. Nanogel of TiO2 shell is chemically unstable in the neutral pH-range and therefore it easily aggregates as separate nanoparticles. However, this instability can be controlled by adding HCl to make the pH value of 3 and the suspension was subsequently ultrasonicated for 15 min at room temperature. Then the suspension was aged at room temperature for 2 h. Finally, the suspension was dried isothermally at 80˚C for 12 h and then the residue was transferred into the furnace at various temperatures for 2 h for calcinations. The thickness of the TiO2 shell size can be varied by changing the concentration of TTIP precursors. 5. Preparation of ZnO/MoO3 core/shell Nanostructures To fabricate core/shell nanostructures, ZnO nanoparticles were dispersed in 100 mL of distilled water by ultrasonication. Then the shell materials were added drop-wise on the above synthesized ZnO dispersion and the pH of 3 of the solution was brought down from 10 by adding HCl. Then the suspension was aged at room

temperature for 2 h. Finally, the suspension was dried isothermally at 80˚C for 12 h and the remaining residue was transferred into the furnace at various temperatures for 2 h calcinations. The thickness of the MoO3 shell size was varied by changing the concentration of MoO3 precursors. 6. Fabrication of one dimensional V2O5-TiO2 Core shell Nanostructures V2O5 nanorods were synthesized by a hydrothermal method. The reagent, such as 0.6 M of ammonium meta-vanadate, was dissolved in 50 mL of distilled water supersaturated with a drop of nitric acid into the solution. After stirring for 2 h, the solution was transferred into a Teflon lined stainless steel autoclave. The autoclave was placed into an oven and kept at 160°C for 24 h, then allowed to cool down to room temperature. The nanoparticles (?) were washed with distilled water and ethanol several times and then dried in an oven at 60°C for 2 h. Nanomaterials Characterization: The variation of surface potential with pH was analyzed by Zeta potential analyzer (Malvern instruments). The structural analysis of the prepared core/shell nanostructures were characterized by powder X-Ray diffraction (Brukers) technique The morphology and micro-structure of the prepared core/shell nanostructures were imaged and analyzed by Field Emission Scanning Electron Microscopy (FESEM, Hitachi s6600) and Transmission Electron Microscopy (TEM, FEI). X-Ray Photoelectron Spectroscopic Studies (XPS) were carried out (Omicron nanotechnology) using monochromatic AlK α-excitation. UV-Vis Absorption spectra were obtained using UV-Vis Spectrophotometer (Perkin Elmer UV 600) to detect the absorption above the range of 250-800 nm. Photocatalytic studies: The Photocatalytic efficiency of fabricated core/shell nanostructures was evaluated by the degradation of Acridine Orange (AO) under solar irradiation. All the experiments were carried out in a homemade photo-reaction apparatus. The reaction cell was placed in a sealed black box with top opened, and the convergence lens was placed to provide maximum intensity of solar light irradiation. In a typical process, 150 mL of (0.03 mM) AO dye solution and 150 mg of core/shell nanostructures was stirred for about 1 h. After dispersing in an ultrasonic bath for 15 min, the solution was stirred for 2 h in the dark to get absorption equilibrium between the catalysts and the solution and then it was exposed to irradiation. Samples (5.0 mL) were collected before and at regular intervals with the degradation being monitored by measuring the absorbance using UV–Vis spectrophotometer (Perkin

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Elmer). The absorbance of AO was followed at 491 nm wavelength.

RESULTS AND DISCUSSIONS

1. ZnO-TiO2 Core shell Nanostructures The size and morphology of the core/shell nanostructures were analyzed and it was found that they exhibited a well-defined spherical morphology with an average size about 5-10 nm for pure TiO2 and 40-50 nm for ZnO nanoparticles. ZnO/TiO2 core shells were obtained with three different shell thicknesses as shown in TEM images (Fig. 1 (a) – (c)). These nanostructures have interfaces and thus exhibited a significant feature of the core / shell structure. The thickness of the outer shell is in the range of ~ 2-3 nm for ZnO/TiO2-1, ~ 3-4 nm for ZnO/TiO2-2 and ~ 5-6 nm for ZnO/TiO2-3, respectively. From the magnified TEM image, we were able to see that TiO2 shell layer thicknesses are well distributed on the surface of ZnO nanoparticles. XRD patterns confirmed the single phase pure ZnO and TiO2 nanoparticles. All the diffraction peaks can be indexed as the hexagonal wurtzite phase (Pattern ZnO) of ZnO structure (JCPDS standard card no. 36-1451). In the case of TiO2 (Pattern TiO2), the peaks (101) and (103) are characteristic lines of the Anatase phase (JCPDS card no. 21-1272). No impurity peaks were detected. Patterns (ZnO/TiO2 -1), (ZnO/TiO2 -2) and (ZnO/TiO2 -3) belonged to the prepared ZnO/TiO2 core/shell nanostructures obtained by adding different concentrations of TTIP via a wet chemical route. The peak intensities increased with shell thickness. Zeta potential variation of ZnO and TiO2 gel was measured for different pH values.

Figure1 (a) – (c) Core shells of ZnO/TiO2, (d) XRD patterns of ZnO/TiO2 Core shells, and (e) Photocatalytic degradation of AO for different irradiations and efficiency data

It was observed that the surface charges are the key factor for electrostatic interaction and subsequent core shell formation. Our preliminary studies showed that there should be a significant difference in the surface charges between the surface of the core and shell solution in order to get the core-shell nanostructures. In the present work, at a pH value of 3, the surface potential of ZnO and TiO2 are – 3.14 mV and 27.2 mV respectively. While we combine these solutions, potential interaction and nullification resulted in the formation of a layer on the core. The shell thickness variation also depends on the core – shell initial materials ratio and temperature in addition to the pH. The photocatalytic degradation of AO with ZnO/TiO2 core shells is shown in Fig 1 (e). Changes in the absorption spectra of AO as a function of irradiation time in the presence of pure and ZnO-TiO2 core/shell nanostructures were presented. It has been observed that irradiation of aqueous suspension of AO in the presence of ZnO/TiO2 nanoparticles leads to a decrease in absorption intensity. It can be seen that the maximum absorption at 491 nm gradually decreases with the irradiation time and AO was found to disappear almost completely after 120 min which indicated that the AO dye has almost completely degraded. It should be noted that a 96% to 100% degradation was observed within 120 min of irradiation time which is much shorter compared to the degradation of AO with pure ZnO or with pure TiO2 nanomaterials. The optimal TiO2 shell thickness to reach the maximum photocatalytic activity in the ZnO/TiO2 core/shell nanostructures is around 6 nm. Under solar-light irradiation, photogenerated electrons pass from the conduction band of TiO2 to the corresponding band of ZnO and hole transfer occurs from the valence band of ZnO to TiO2. The simultaneous transfer of electrons and holes in the ZnO/ TiO2 system should increase both the yield and the lifetime of charge carriers. The photogenerated electrons were captured by the adsorbed oxygen molecules and the holes were trapped by the surface hydroxyl, both resulting in the formation of high oxidative hydroxyl radical species (˙OH) which show the poor selectivity for the attack of dye molecules. Thus, the photocatalysis efficiency is significantly enhanced [4]. 2. ZnO-MoO3 core shell Nanostructures ZnO/MoO3 core shell nanoparticulates have been synthesized by a wet chemical route at room temperature and the shell thickness of MoO3 can be controlled by changing the ratio of MoO3 precursors from 0.5-2 M%. Well defined spherical morphology of the ZnO particles with three different MoO3 shell thickness were imaged by HRTEM (Fig. 2 (a) – (c)). But not much variation was seen in the X-ray

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diffraction peaks owing to the small percentage of MoO3 concentration.

Figure 2 (a) – (c). Core shells of ZnO/MoO3, (d) XRD patterns of ZnO/MoO3 Core shells, and (e) Photocatalytic degradation of AO for different irradiations and efficiency data. The photocatalytic degradation of AO was studied using fabricated particles and UV irradiations. The photocatalytic activity of the AO is also attributed to the synergistic effect caused by the combinations of MoO3 on ZnO surfaces. During the UV irradiation process, the ZnO species captured electrons and carried them to MoO3 species to reduce Mo6+ to Mo5+ and Mo4+ [5]. The capability of Mo6+ capturing electrons is enhanced by ZnO species which leads to a higher catalytic activity. The increases in the redox potential and synergistic effect of ZnO/MoO3 are the major factors for the degradation of organic dye molecules. Moreover, heterostructured core/shell ZnO/MoO3 nanostructures are insoluble in water and could be separated easily. 3. V2O5-TiO2 one dimensional (1D) ore shell Nanostructures Nanorods (1D) pure vanadium penta-oxide (V2O5) and 1D core shells of V2O5/TiO2 were fabricated using a hydrothermal technique and hydrothermal- sol-gel approaches, respectively. FESEM and HRTEM images show the one dimensional V2O5/TiO2 core/shell nanostructures (Fig. 3 (a) – (c)). By changing the process variables, it was possible to obtain long platelets of V2O5. TiO2 was coated on V2O5 using a simple process. X-ray diffraction peaks. (Fig.3d). Both V2O5 and V2O5/TiO2 photocatalyst have n-type semiconductors and also have a higher UV absorption efficiency than that for visible light. The absorption of visible light on V2O5/TiO2 is higher than that on pure V2O5. Figure 3 (e) shows the photocatalytic spectrum, in which there was no degradation of organic dye for pure V2O5 nanorods. While we used the core shell of V2O5/TiO2, almost 40% degradation occurred within 20

min and after that there was a slow degradation with time. Further experiments are required with different shell thicknesses to elucidate the role of shell

Figure 3 (a) – (c). Core shells of ZnO/MoO3, (d) XRD patterns of V2O5/TiO2 Core shells and (e) Photocatalytic degradation of AO for different irradiations and efficiency data, thickness on the degradation. During the UV irradiation process, the TiO2 species captured electrons and carried them to V2O5 species to reduce V5+ to V4+. The capability of V5+ capturing electrons is enhanced by the influence of TiO2 species, leading to higher catalytic activity. Owing to their strong oxidizing power, holes quickly react with adsorbed water molecules to produce hydroxyl radicals (-OH), which in turn oxidize organic pollutants in the vicinity.

CONCLUSION

This paper mainly highlights our latest work on core shell nanostructuring of metal oxide semiconductor materials. Solution-based routes with simple three steps were used to fabricate the core-shell nanostructures. These core shell nanostructures have been demonstrated to have excellent photocatalytic degradation of organic dyes under UV and solar radiations.

REFERENCE

1. S. Karele, S. W. Gosavi, J. Urban, S. K. Kularni, Curr. Sci. 91 (2006) 1038

2. R. G. Chaudhuuri, S. Paria, Chem. Rev. 112 (2012) 2373

3. C. M. Ma, Y. Ku, Y.C. Chou, F.T. Jeng, J. Environ. Eng. Manage. 18 (2008) 363

4. R. Ajay Rakkesh, S. Balakumar, Unpublished work 5. J. Huang, X. Wang, S. Li, Y. Wang, 257 (2010) 116

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Studies on Melt-quenched AgInSbTe System

C. Rangasami, Mahaveer K Jain and S. Kasiviswanathan

Department of Physics, Indian Institute of Technology Madras, Chennai-36, Email: [email protected]

Abstract. Phase homogeneity and crystal structure of melt-quenched AgInSbTe system have been analyzed using X-ray diffraction (XRD) and Raman spectroscopy. Rietveld refinement of crystal structure of Ag4In12Sb56Te28 has revealed the formation of AgIn3Te5, Sb8Te3 and Sb phases respectively with P-type tetragonal ( 42P c ), 11R ( 3R m ) and A7 ( 3R m ) structures. Addition of suitable amount of Te to Ag4In12Sb56Te28 yielded Ag3.54In10.62Sb49.56Te36.28, alloy with AgIn3Te5

and Sb8Te3 phases. Optical micrographs of surface of the samples have shown the existence of three kinds of regions (AgIn3Te5 rich, Sb8Te3 rich and Sb rich regions) with different reflectivity. Presence of multiphase and effect of laser-sample interaction at these regions have been investigated using Raman spectroscopy. Analysis of Raman spectra has revealed that the regions with more content of AgIn3Te5 exhibit amorphous phase during laser-sample interaction.

Keywords: AgInSbTe, Rietveld refinement, Raman spectroscopy, Laser-sample interaction. PACS: 61.66.Dk, 64.70.Kd, 64.70. Kg.

INTRODUCTION

At room temperature, some materials exhibit amorphous phase even though they can have thermodynamically stable crystalline phase. Materials of this kind with a capability of fast switching between amorphous and crystalline phases with unique optical and electrical properties are called phase change memory materials (PCMMs). These are excellent active layer materials in rewritable optical data storage media such as digital versatile disks and Blue-ray disks, and in phase change random access memory [1]. GeSbTe based ternary and AgInSbTe based quaternary systems are recognized as potential PCMMs for optical and electronic storage media applications [1]. Among these, AgInSbTe alloys possess certain unique characteristics: growth-dominated crystallization, low melting point, large crystalline or amorphous phase stability at room temperature and therefore, are widely used in optical data storage. One such example, where these device properties have been optimized, is Ag3.5In3.8Sb75.0Te17.7 [1]. AgInSbTe alloys, depending on the composition, crystallize in single phase or in multiple phases. For example, Ag5In6Sb59Te30 and Ag3.4In3.7Sb76.4Te16.5 have shown single phase, but with different crystal structures (hexagonal and A7 structures) whereas alloys with higher Ag/In content, like Ag8In13Sb49Te30, are found to be heterogeneous. There appears to be no correlation between the starting composition and the segregated phases. For instance, Ag8In13Sb49Te30 showed AgInTe2, AgSbTe2 and Sb

phases, whereas AgTe, InTe, InSb and Sb2Te3 phases have been reported for Ag8In8Te46Sb38. The interest here is to investigate the phase and crystal structure of some AgInSbTe alloys with compositions similar to those exhibiting heterogeneity [2] so that insights into the nature of the segregated phases can be gained.

EXPERIMENTAL DETAILS

Ag4In12Sb56Te28 and Ag3.54In10.62Sb49.56Te36.28 alloys were synthesized by melt-quench method. Powder diffraction data were recorded (2θ = 10 to 130º and step size 0.017º) using PANalytical (X'Pert PRO) XRD unit with Cu-Kα radiation. Rietveld refinement of crystal structure was carried out using a widely used software GSAS. Raman measurements were carried out using a Horiba Jobin Yvon, model HR800 UV Raman microscope equipped with a grating consist of 1800 grooves/mm in backscattering geometry. Raman spectra were recorded using an Ar-ion laser beam of power of 0.5 mW, focused to a spot size of ~2 μm.

RESULTS AND DISCUSSION

Initial analysis of XRD data of Ag4In12Sb56Te28 alloy revealed the presence of AgIn3Te5, Sb8Te3 and Sb phases. Rietveld refinement of crystal structure of Ag4In12Sb56Te28 was carried out based on the space groups 42P c and 3 .R m Results of refinement (Rwp= 6.41%) along with XRD data are shown in Fig. 1a, which are congruent with the results drawn from the

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 38-39 (2013); doi: 10.1063/1.4790899

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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initial analysis. The structures and lattice parameters of the identified phases were verified with the reported [3] and JCPDS data. Addition of suitable amount of elemental Te yielded Ag3.54In10.62Sb49.56Te36.28 which is expected to have AgIn3Te5 and Sb8Te3 phases alone. Results of crystal structure refinement (Rwp= 7.59%) along with XRD data of Ag3.54In10.62Sb49.56Te36.28 is shown in Fig. 1b. The above observations revealed that elemental Sb has been reformed into Sb8Te3 after addition of excess Te, which can be verified with the reflections at 2 = 23.706º, 40.128º and 41.930º in the XRD data (please refer insets given in Fig. 1a and 1b).

FIGURE 1. Results of Rietveld refinement along with XRD data of (a) Ag4In12Sb56Te28 & (b) Ag3.54In10.62Sb49.56Te36.28. The insets show the XRD data on an expanded scale (2θ = 23° to 26° and 38° to 44°).

Optical micrograph of Ag4In12Sb56Te28 (Fig. 2a) shows the presence of three kinds of regions (marked as x, y and z) with different optical reflectivities. Raman spectra were recorded at these regions in order to comprehend the phases formed and to understand the effect of laser-sample interaction. Laser (488 nm) beam of powers of 0.5 mW and 20 mW were used to acquire information and to introduce the changes on the sample surface respectively. A constant integration time of 200 s was used to record the spectra before and after interaction whereas 50 s was used to record the spectra during interaction. All three measurements (before, during and after interaction) were performed alternately on the same spot. Raman spectra of as-formed Ag4In12Sb56Te28 recorded at the regions x, y and z are shown in Fig. 2b to 2d. Deconvolution of the Raman spectra yielded peaks at 125.8, 132.2, 142.2, 151.2 and 185.4 cm-1 for the region x, 125.6, 132.8, 142.6, 151.4 and 156.6 cm-1 for the region y and 125.6, 132.3, 142.1 and 156.0 cm-1 for the region z. These peaks represent the phases AgIn3Te5, Sb8Te3 and Sb. The highest intensity peak at 125.1 cm-1(A1 mode of AgIn3Te5) suggest that the content of AgIn3Te5 is high in the region x. Similarly, the highest intensity peaks at 151.2 and 156.6 cm-1 (A1g modes of Sb and Sb8Te3) observed in the spectra recorded from the regions y and z suggested that contents of Sb and Sb8Te3 are large in those regions, respectively. Raman spectrum recorded at the region x during interaction shows a featureless broad spectrum as shown in Fig. 3a. The broad spectrum exhibited by the sample reveals that

the region with more content of AgIn3Te5 has become amorphous locally during the laser-sample interaction.

FIGURE 2. (a) Micrograph of Ag4In12Sb56Te28. Raman spectra of as-formed Ag4In12Sb56Te28 acquired at regions x (panel b), y (panel c) and z (panel d).

The peaks observed in the Raman spectrum recorded after interaction (Fig. 3b) reveals that the region under investigation (x) is re-crystallized locally. On the other hand, the spectra recorded at the region y during and after interaction (Fig. 3c) exhibit peaks correspond to oxide phases such as Sb2O3, in addition to the initial phases (i.e. region y exhibits crystalline phase always). Similarly, the Raman spectra recorded from the region z was found to exhibit same feature as that of y. The above observations were found to be true in the case of Ag3.54In10.62Sb49.56Te36.28 also.

FIGURE 3. Raman spectra of Ag4In12Sb56Te28 acquired at region x during (panel a) and after (panel b) laser-sample interaction. Raman spectra recorded at region y after (panel c) laser-sample interaction.

The above results have shown that regions with large phase fraction of AgIn3Te5 become amorphous during laser-sample interaction, but the starting phases remain nearly same after the interaction. Regions with larger amount of Sb and Sb8Te3 phases have shown significant growth of -Sb2O3 during and after laser-sample interaction. These observations have been explained based on the maximum temperature rise at different regions during laser-sample interaction.

REFERENCES

1. Siegrist, T., P. Merkelbach, and M. Wuttig, Annu. Rev.Condens.Matter Phys., 3, 11.1–11.23 (2012).

2. Her, Y.C., H. Chen, and Y.S. Hsu, J. Appl. Phys., 93, 10097-10103 (2003).

3. Kifune, K., Y. Kubota, T. Matsunga, and N. Yamada, Acta Crystallogr. Sec. B, 61, 492-497 (2005).

23 24 25 26

20 40 60 80 100 120

ba

20 40 60 80 100 120degdeg

In

tens

ity (a

.u.)

23 24 25 26

38 40 42 44

38 40 42 44

100 150 200 250Raman shift (cm-1)

Inte

nsity

(a.u

.)

(d)

100 150 200 250

Inte

nsity

(a.u

.)

Raman shift (cm-1)

(b)

100 150 200 250

Inte

nsity

(a.u

.)

Raman shift (cm-1)

(c)

(a)

100 200 300In

tens

ity (a

.u.)

Raman shift (cm-1)

(c)Sb2O3

100 200 300Raman shift (cm-1)

Inte

nsity

(a.u

.) (a)

100 200 300

Inte

nsity

(a.u

.)

Raman shift (cm-1)

(b)

39

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High-pressure Electrical Resistivity Studies on FeSe2 and FeTe2

G.Parthasarathy1 , D.K. Sharma2 , Y.K. Sharma2 and Usha Chandra2

1CSIR-National Geophysical Research Institute, Hyderabad- 500007, India ([email protected])

2Department of Physics, University of Rajasthan , Jaipur- 302004, India

Abstract. We report here for the first time the pressure dependence of the electrical resistivity of ferroselite (FeSe2) and frohbergite FeTe2 up to 8 GPa. The synthetic ferroselite shows a pressure induced marcasite-to- NiAs type structural phase transition at 6.8 GPa and frohbergite shows the transition at 5.7 GPa. The transition was observed with a discontinuous resistivity decrease by 0.9 times. We also present here the XRD results on the FeSe2 and FeTe2. The relevance of the phase transition to Martian mineral chemistry is discussed. Keywords: High-pressure ; marcasite; mineral physics, phase transitions, chalcogenides. PACS: 64.70kg;64.70K; 91.60Hg;91.60Gf;72.80.

INTRODUCTION

The mineral ferroselite (FeSe2) is known to form

in the vicinity of oxidizing sulfide and uranium deposits. Under reducing conditions, elemental Se either is incorporated within pyrite or forms the ferroselite (FeSe2).The minerals ferroselite and frohbergite FeTe2 are found as accessory minerals in uranium deposits [1]. Studies on the high-pressure phase stability of Iron chalcogenides at mantle pressures are very relevant to understand the role of chalcogens in mineral chemistry of the Martian Core and subsurface geological processes [2]. In this work we report for the first time the high-pressure electrical resistivity measurements on the synthetic ferroselite FeSe2 and frohbergite FeTe2. Both ferroselite and frohbergite have the marcasite type structures with orthorhombic unit cell with Pnnm space group. To the best of our knowledge there are no previous report on the high-pressure electrical resistivity studies on ferroselite FeSe2 and frohbergite FeTe2.

.

EXPERIMENTAL METHODS

High purity (� 99.999%) elements were weighed in stoichiometric proportion corresponding to FeSe2 and FeTe2 compositions of the alloys and were sealed under vacuum (�10 -2 Torr) in quartz ampoule. The ampoules were kept in Kanthal wire wound

resistive furnace. Initially the temperature was slowly raised from 300K to 1273K in the time interval of about 30 hours to ensure solid state diffusion of Se and Te. The temperature was fixed at 1273K for 30 hours which ensured the complete melting and then the ampoules were quenched into ice water. The furnace temperature was controlled by a temperature controller (� within ±10K). The black ingot , thus, obtained was crushed into fine powder and put again into evacuated quartz ampoules and were annealed at 873K for two weeks and quenched into water. The annealed ingots were crushed into fine powder using agate mortar and pestal in methanol and were dried at 350K. X-ray powder diffraction patterns were recorded at 300K for these specimens using a Phillips 1840 model diffractometer (operated at 30 kV and 30 mA) by varying the 2� in the step of 0.02o from 10o to 70o. XRD data were analyzed using a standard program.

High-pressure electrical resistivity measurements were carried out in an opposed anvil cell with tungsten carbide anvils, with steatite as pressure transmitting medium. The calibration and methodology of the high-pressure four probe electrical resistivity measurements were discussed elsewhere [3-5].

Results and Discussions

Powder X-ray diffraction patterns show all the

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 40-41 (2013); doi: 10.1063/1.4790900

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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major reflections corresponding to the crystal structure with orthorhombic marcasite phase , with unit cell parameters were determined to be a= 0.479(8)nm; b=0.578(5)nm; c=0.358(5) nm for FeSe2 and a= 0.526(5)nm; b=0.626(6)nm; c= 0.386(8)nm for FeTe2 . The conductivity activation energy for electrical conduction for FeSe2 is found to vary from 0.50 to 0.45 eV in the temperature range 300 to 400 K for FeSe2 and 0.35 eV for FeTe2 in the temperature range 300 to 400K. Figure-1 shows the pressure dependence of the normalized electrical resistivity of FeSe2 and FeTe2 up to 8 GPa at room temperature. It is well known that pure Te shows the pressure induced insulator-metal transition at 4.0 GPa [6,7]. The high-pressure phase was determined to be monoclinic and pure iron shows the phase transition from bcc to hcp phase at 13GPa with the sharp electrical resistivity increase at the transition pressure [8]. In case of Te it is both structural and electronic phase transition at 4GPa [7]. Our earlier study on CrSb2 demonstrated a pressure induced marcasite to pyrite transition at 6.8GPa. Since FeSe2 and FeTe2 have the marcasite structure at room temperature, the observed phase transition is interpreted as pressure induced structural phase transition from Marcasite [9] to thermodynamically stable phase NiAs type phase for dichalcogenides. In order to establish the insulator to metal transition [10], data on temperature dependence of the electrical resistivity at different pressures are needed and are under progress. FIGURE 1. Pressure dependence of the normalizedelectrical resistivity . R0 is the value of the room temperature resistivity.

Kumar et al. have studied high-pressure behaviour of FeSe sample and found pressure induced enhancement in superconductivity due to a pressure-induced distortion of the low-temperature Cmma phase at around 1.6GPa and the appearance of a high-pressure Pbnm phase at 9 GPa [11]. However, there are no previous reports on the high-pressure behaviour of FeSe2.

Earlier high-pressure studies on pyrite FeS2 predicted the pressure-induced metallization at about 14-30 GPa[12]. Mechanical alloying by ball milling induced a phase transition of FeSe2 from marcasite-to-NiAs type, for the milling time of 52 hours [13]. However, further EXAFS studies do not reproduce the phase transition in the FeSe2-FeSe system up to 19 GPa, but the pressure induced disorder-order transition as a function of milling time [14]. The Pauling electronegativity of oxygen is 3.44, where as that of S is 2.58, Se is 2.55, and Te is 2.1. Hence the phase transition pressure should decrease from Selenide to telluride, as observed in the present study (Fig.1). This work has implications to the core of the Mars, as it has been inferred that the core of the Mars is very rich in Iron-Nickel-chalcogenides. Further work on high-pressure Mössbauer spectroscopy and XRD to understand the nature of the phase transition in iron dichalcogenides are under progress.

ACKNOWLEDGMENTS

The authors thank CSIR, ISRO, PLANEX for funding the research. We are thankful to Professor Mrinal Sen , Director, CSIR-NGRI for his very kind encouragements and support. GP thanks Professor Charles Prewitt , Geophysical Laboratory , CIW, USA for suggesting the marcasite problem.

REFERENCES 1. D.J. Vaughan Review Mineralogy and Geochem 61,

1-5 (2006). 2. P.L. King and S.M. Mclennan, Elements, 6, 107-112

(2010) 3. G. Parthasarathy J.Appl Geophysics, 58, 321-329

(2006). 4. G. Parthasarathy. Mater Lett 61, 4329-4331 (2007). 5. G. Parthasarathy. Am Mineralogist 96, 860-863

(2011). 6. G. Parthasarathy and W.B. Holzapfel. Physical Rev

B37, 8499-8501(1988). 7. G. Parthasarathy, K. J. Rao and E.S.R. Gopal. Solid

State Commun. 52, 867 -871 (1984). 8. U.Chandra, et al. Am Mineralogist. 95, 870-875

(2010) 9. U.Chandra, et al. Phil Mag Lett 83, 273-279 (2003) 10 G. Parthasarathy and E.S.R. Gopal. Bull Mater. Sci 7,

271-302 (1985). 11. J. Kumar et al. J. Phys. Chem. B 114, 12597-606

(2010) 12. P. Cervantes et al. J. Phys. Chem. Solids. 63, 1927-

1933 (2002). 13. C.E.M. Campos et al. Solid State Commun. 128, 179-

182 (2002). 14 CEM Campos et al. J.Phys. Condensed Matter 16,

8485-8490 (2004).

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Investigation of Dielectric and Structural Behaviour of Lead free (Ba1-xCax)(Zr0.05Ti0.95)O3 Ceramics

Kamal Jain1, Gurvinderjit Singh2, G. K. Upadhyaya1and V. S. Tiwari2

1School of Studies in Physics, Vikram University, Ujjain 2Laser Materials Development & Devices Division

Raja Ramanna Centre for Advanced Technology, Indore-452013 Email: [email protected]

Abstract. The dielectric and structural behaviour of calcium doped Ba(Zr0.05Ti0.95)O3 i.e (Ba1-xCax)(Zr0.05Ti0.95)O3 piezoelectric ceramic have been investigated. The dielectric measurements show that T�O and R�O transition temperatures decreasing with increase in Ca2+ content, while C�T temperature remains nearly same. The dielectric constant and piezoelectric coefficients show an anomaly near x=0.08, attributed to the presence of phase co-existence at this composition. Keywords: Lead free materials, Barium titanate, Piezoelectric coefficients PACS: 77.65 -j, 77.84 -s, 61.05cp

INTRODUCTION

Barium titanate (BaTiO3) is one of the most widely studied lead-free piezoelectric material [1]. It shows polymorphic phase transitions. From high temperature cubic phase, it transforms to a tetragonal (C�T) phase at 405K, to an orthorhombic phase (T�O) at 273K, and finally to a rhombohedral phase (O�R) at 200K. A common approach to generate high piezoelectricity in BaTiO3 is to shift the T�O phase transition boundary near the room temperature by adding couple of dopants. It is known that the addition of Zr4+ at titanium (Ti4+) site shifts the T�O and O�R phase transition temperatures towards high temperature side, while lowering the C�T transition temperature [1]. Thus, by varying the amount of Zr4+ it is possible to alter the T�O transition temperature with improved piezoelectric properties. Recently, Yu et al [2] have studied the effect of Zr4+ incorporation on dielectric and piezoelectric properties of BaTiO3. They observed optimum properties for 5mol% Zr4+ doped BaTiO3 i.e. Ba(Zr0.05Ti0.95)O3 (BZT). For this composition the T�O phase transition temperature is 30K above the room temperature (300K). Therefore, further improvement in the properties is possible by shifting the T�O phase transition temperatures near 300K. Generally, calcium (Ca2+) doping is used to lower the T�O transition temperature without affecting the Curie temperature. Li et al [3] have found that the piezoelectric properties of this composition i.e. Ba(Zr0.05Ti0.95)O3 can further be improved by doping

with calcium (Ca2+) and it is highest for 8mol% of doping. But their study lack of detail analysis of dielectric and structural behaviour. These investigations will established a correlation between structure and the piezoelectric properties.

EXPERIMENTAL

The (Ba1-xCax)(Zr0.05Ti0.95)O3 ceramics with x =0.03, 0.05, 0.08, 0.10, 0.12 and 0.15 were prepared by conventional solid state reaction technique. The stoichometric amount of BaCO3, CaCO3, ZrO2 and TiO2 were ball-milled with zirconia balls in ethanol for 10hours. The dried slurry was then calcined at 1350oC (6hours). Calcined powders were compacted in the form of disks of diameter 15 mm and thickness 1-2 mm. These disks were sintered, in ambient atmosphere, at 1500oC for 10 hours. The density of the sintered samples was measured by liquid displacement method and found to be ~95% of the theoretical values. The sintered specimens were electroded and then subjected to dielectric measurements at different frequencies in the temperature range of -80 to 140oC using HP-4194A impedance analyser. The room temperature x-ray diffraction was carried out using rotating anode (Rigaku-geigerflex) power x-ray diffractometer. The samples were also poled at 130oC under an electric field of 6kV/cm to measure d33 values using Piezotest make (PM-200) d33 meter.

RESULTS and DISCUSSION

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 42-43 (2013); doi: 10.1063/1.4790901

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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150

200

250

0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

60

75

(b)

-d31

(pm

/V)

d 33

(pm

/V)

x

82.5 84.0 85.5

(222)

2�

44.5 45.0 45.5 46.0

2�

0.03

K��

0.05

0.08

0.10

0.12

0.15

(200)

(b)

Fig.1a shows the powder x-ray diffraction of (Ba1-xCax)(Zr0.05Ti0.95)O3. The x-ray diffraction patterns revealed a single perovskite phase formation with no signature of impurity phase in any of the compositions. The data was indexed for cubic perovskite as observed in paraelectric phase. The x-ray diffraction pattern of (111) and (200) reflections is shown in Fig.1b. It is evident from figure that for x=0.03 and 0.05 the (200) reflections are broad but two distinct peaks having almost equal intensity are present. This suggests the existence of orthorhombic phase with lattice parameters a � b � c in both the compositions. The (200) diffraction peak splits into (002) and (200)/(020) with intensity ratio 1:2 for compositions higher than x � 0.08, indicating tetragonal structure. On the other hand, the (222) reflections show a diffuse hump at lower ����side for x=0.05 and 0.08 compositions, indicating presence of mixed crystallographic phases as observed near MPB. However, for x=0.03, 0.10, 0.12 and 0.15 it is nearly singlet with asymmetric broadening towards higher angle side. This broadening is due to K�� contribution, marked by arrow in the figure. The x-ray line profile analysis reveals that there is an orthorhombic-to-tetragonal crossover in (Ba1-xCax) (Zr0.05Ti0.95)O3 with phase co-existence near x=0.08. Fig.1 (a)Powder x-ray diffraction & (b) Evaluation of x-ray diffraction profile for (200) and (222) reflection of (Ba1-

xCax)(Zr0.05Ti0.95)O3 ceramics Fig. 2a&b show the variation of room temperature dielectric constant���RT�, d33 and d31. It is evident from the figure that ��RT�, d33 and d31first increase with 'x' and attain their maximum at x =0.08. Beyond this a gradual decrease in �RT, d33 and d31 values is observed. Clearly, an anomaly in their values

Fig.2 Variation of (a) �RT and (b) d33, d31 with 'x'

is observed near x=0.08. The value of �RT increases from 1830 for x=0.03 to 2320 for x=0.08. The phase transition temperatures, measured from peak position of dielectric constant during cooling, from cubic-to-tetragonal (TC�T), tetragonal-to-orthorhombic (TT�O) and orthorhombic-to-rhombohedral (TO�R) are summarized in Fig.3. It is seen from the figure that there is very weak shift in the temperature of TC�T transition towards higher temperature side with increase in the calcium content. On the other hand, TT�O and TO�R decreases monotonically with increase in calcium content. The rate of decrease of TT�O and TO�R is much sharper than decrease in TC�T. It is clear from the figure that TT�O decreases from 53oC for x=0.0 to 2oC for x=0.12. When x=0.08 the TT�O phase transition temperature (19oC) locates near room temperature (27oC), such that two phase co-existence can exists as identified by XRD analysis. Fig. 3 Variation of TC�T, TT�O and TO�R with 'x'

CONCLUSIONS Based on above measurements, it can be realized that maximum in dielectric an piezoelectric properties for (Ba1-xCax) (Zr0.05Ti0.95)O3 is caused by shifting the polymorphic phase transition (T�O) close to room temperature. Near polymorphic phase transition, phase co-existence occurs and the energy barrier of two phases are very close to each other making polarization jump easily from one state to other on application external electric field.

REFERENCES

1. B. Jaffe, Piezoelectric Ceramics, Academic Press, London (1971).

2. Z. Yu, C. Ang, R. Guo, and A. S. Bhalla, J. Appl. Phys., 92, 1489(2002).

3. W. Li, Z. Xu, R. Chu, P. Fu and G. Zang, J. Am. Ceram. Soc., 93 (2010) 2942.

4. B. Noheda, D. E. Cox, G. Shirane, J. Gao and Z. G. Ye, Phys. Rev. B, 66, 054104 (2002).

5. L. Mitoseriu, P. M. Vilarinho and J. L. Baptista, Appl. Phys. Lett., 80, 4422 (2002).

2 0 3 0 4 0 50 60 7 0 8 0 90

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)(300

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(a )

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2000

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Influence of Anthracene Doping on the Order-Disorder Phase Transition in Phenanthrene

Rajul Ranjan Choudhury, R. Chitra, Lata Panicker and V. B. Jayakrishnan

Solid State Physics Division, Bhabha Atomic Research Center, Trombay Mumbai,400085

Email:[email protected]

Abstract. A comparison between Anthracene and Phenanthrene structures demonstrates how molecular shape and molecular packing in the crystal could lead to the presence or absence of large amplitude molecular movement within the crystals. Anthracene doping in Phenanthrene crystals results in an expansion of the unit cell, hence the steric constrain on molecular rotation is eased out with the increase in the dopent concentration. As a result Phenanthrene molecules in doped crystallites can reorient more freely at room temperature, hence the disordered phase of Phenanthrene crystal is stabilized at room temperature it self.

Keywords: molecular shape, molecular packing, order- disorder phase change. PACS: 64.60.Cn, 64.70.kt

INTRODUCTION Phenanthrene (C14H10) is a polycyclic benzenoid hydrocarbon with three hexagons; it is isomeric to Anthracene (Figure-1). Phenanthrene crystals undergo an order-disorder structural phase transition at 72°C about 27°C before melting [1], where as no such transition was observed in Anthracene right up to melting. The structural investigation of the phase transition [2] in Phenanthrene crystals has revealed that in the temperature range 72°C to 99°C Phenanthrene crystal behaves like an orientationally disordered crystal with two possible molecular positions within the cell. In order to understand the fundamental mechanism of the phase transition we had modeled the molecular movement within the Phenanthrene crystal and estimated the rotational potential energy surface for a Phenanthrene molecule as it undergoes this flip-flop motion [3]. Situation in Phenanthrene crystal was explained by a model where the molecules exhibit large amplitude librations having been trapped in the potential wells. Fluctuations in the orientation of the neighbouring molecules result in changes in the shape of the potential well and consequently giving rise to angular motions of molecules with large amplitude. Under ambient conditions Phenanthrene crystallizes into a noncentrosymmtric structure with space group P21, where as Anthracene crystallizes into a centrosymmetric P21/n structure. This difference in crystal symmetry of these two structural isomers in mainly due to the difference in the molecular

symmetries of the two molecules, Phenanthrene has a molecular symmetry of mm2 where as Anthracene has a molecular symmetry mmm. Molecule with higher symmetry is expected to be more closely packed in the crystalline phase than the one with a lower symmetry, this fact is reflected in their melting points, melting point for Phenanthrene crystals is 99°C and that of Anthracene is 218°C, although the boiling point for both Anthracene as well as Phenanthrene is the same (340°C) indicating that the strength of intermolecular interactions is similar for the two. It has been reported that Anthracene doping in Phenanthrene crystals has a significant effect on the phase transition in Phenanthrene [4]. We have analyzed the influence of Anthracene doping on the structural phase transition in Phenanthrene in the light of the proposed mechanism of the structural phase transition.

Figure-1 Anthracene & Phenanthrene molecules

EXPERIMENT Mixed crystals of Phenanthrene and Anthracene were obtained from solutions of Phenanthrene and Anthracene in toluene. Phenanthrene to Anthracene ratio in the solutions were varied as following 1.0:0.0

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 44-45 (2013); doi: 10.1063/1.4790902

© 2013 American Institute of Physics 978-0-7354-113-3/$30.00

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(sample-0), 0.9:0.1 (sample-1), 0.8:0.2 (sample-2), 0.7:0.3, (sample-3) 0.0:1.0 (sample-5). In order to ascertain the existence of the order-disorder phase transition DSC and X-ray powder diffraction measurements were conducted on the polycrystalline powder obtained from the slow evaporation of the solutions under ambient conditions.

DISCUSSION Table-1 lists some of the properties of Phenanthrene as well as Anthracene crystals. Figure 1 illustrates that the width of Phenanthrene molecule is more than that of Anthracene; this is a result of the less symmetric molecular shape of Phenanthrene. Gavezzoti [5] in his analysis of packing in hydrocarbons had defined a self packing coefficients Cself that gave an estimate of the smoothness of the molecular envelope which plays a decisive role in the close packing of the molecular units in simple hydrocarbons. A molecule with high symmetry usually has a higher value of Cself and a more closed packed structure. Lower value of Cself for Phenanthrene results from its less symmetric shape as compared to Anthracene hence the Phenanthrene molecules cannot be as closely packed as the Anthracene molecule and the free space available in Phenanthrene crystal allows the molecule to get orientationally disordered where as lack of the free space in Anthracene prevents such transition in Anthracene.

Figure-2 X-ray and DSC patterns for Anthracene doped Phenanthrene crystallites Table-1 Comparison between Phenanthrene & Anthracene Phenanthrene Anthracene

Molecular formula: C14H10 Molecular formula: C14H10 Melting Point :99°C Melting Point :218°C Boiling Point:340°C Boiling Point:340°C Space Group: P21 Space Group: P21/n Vmol≈ 175.3 Å3 Vmol≈ 175.3 Å3 a=8.441Å, b=6.140Å, c=9.438 Å β=97.96°, VUC=484.4 Å3

a=8.552Å, b=6.016Å, c=11.172 Å β=124.6°, VUC =473.2 Å3

Vfree=(VUC/Z)-Vmol=68.9Å3 Vfree=(VUC/Z)-Vmol=61.3Å3 Cself: 0.478 Cself:0.615 Packing Energy: -97.48KJ/mol

Packing Energy: -103.03KJ/mol

Melting point of Phenanthrene was found to increase with Anthracene doping, the DSC measurement gave the following values for the melting points, Sample-0: 98.44°C, Sample-1: 101.40°C, Sample-2: 107.79°C and Smaple-3: 107.96°C. Figure-2 shows that the order-disorder phase transition in Phenanthrene which occurred at 72°C in pure sample (Sample-0) shifted to a lower temperature 60.75°C for sample-1 which has small Anthracene doping where as no clear-cut transition was observed in Sample-2 and Sample-3 which have higher dopent levels. We have obtained the unit cell parameters for the doped samples (Table-2) using the Le Bail method for the determination of unit-cell parameters from polycrystalline diffraction data. One can see that doping results in an expansion of the unit cell, hence the steric constrain on molecular rotation is eased out with the increase in the dopent concentration as a result phenanthrene molecules in doped crystallites can reorient more freely at room temperature. Gloistein et. al. [4] have reported that for large dopent concentration the disordered phase is stabilized at room temperature, our DSC as well as X-ray measurements concur with their results. Table-2 Cell parameters for Anthracene doped Phenanthrene crystallites Sap a(Å) b(Å) c(Å) Β(°) V(Å3) Samp0 8.4446

(0.0081) 6.1414 (0.0005)

9.4333 (0.0087)

98.12 (0.03)

484.39 (0.90)

Samp1 8.4101 (0.0070)

6.1464 (0.0009)

9.4985 (0.0084)

98.38 (0.03)

485.74 (0.90)

Samp2 8.3840 (0.0198)

6.1418 (0.0010)

9.5512 (0.0215)

98.56 (0.08)

485.33 (2.3)

Samp3 8.3845 (0.0188)

6.1554 (0.0009)

9.6399 (0.0208)

98.80 (0.9)

491.61 (2.3)

REFERENCES 1. S. Matsumoto, Bull. Chem. Soc. Jpn. 40, 2749, (1967). 2. V. Petricek, I. Cisarova, L. Hummel, J. Kroupa, and B.

Brezina, Acta Cryst. B46, 830, (1990), . 3. R. R. Choudhury and R. Chitra, Phase Transitions.

DOI:10.1080/01411594.2012.683869 4. U. Gloistein, M. Epple, and H. K. Cammenga,

Zeitschrift Fur Physikalische Chemie, 214, 379, (2000). 5. A. Gavezzotti, Acta Cryst. B46, 275, (1990).

45

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Study of Structural Phase Transition and Optical Properties in BiFeO3-BiMnO3 Thin Films

V. Annapu Reddy,a and R. Nathb

Ferroelectric Materials and Devices Research Laboratory, Department of Physics, Indian Institute of Technology Roorkee, Uttarakhand 247667, India

[email protected], [email protected]

Abstract. BiFeO3 and BiFeO3-BiMnO3 films were prepared by spray pyrolysis technique and their structural and optical properties were examined. The X-ray diffraction of these films shows that the rhombohedral structure of BFO film is modified and reduced toward the monoclinic or tetrahedral structure at 10 at.% of BiMnO3 with higher crystal symmetry. The structural transition is in favour of reduced oxygen vacancies in BiFeO3 films. The transmission electron microscopy was used to know the crystal structure and the particle size of the films. The band gap in the BiFeO3-BiMnO3 film (Eg�2.55 eV) has significantly increased in comparison to the BiFeO3 film (Eg�2.32 eV).

Keywords: multiferroics, spray pyrolysis, morphotropic phase boundaryPACS: 75.85.+t, 52.77.Fv, 81.15.Rs,�81.40.Vw

INTRODUCTION

The magnetoelectric effect in the multiferroic materials has attracted considerable attention because the consumption of electricity in nonvolatile memories can be drastically reduced if the read or write process can be carried out using an electric field. BiFeO3 (BFO) and BiMnO3 (BMO) are both well-known candidates for multiferroic materials [1-2]. BMO is a monoclinical distorted perovskite in which ferroelectricity persists to low temperatures through the ferromagnetic transition at 105 K. BFO is the most studied multiferroic material because its ferroelectric Curie temperature and anti-ferromagnetic Neel temperature are both well above room temperature [3]. Microscopically, the anti-ferromagnetic spin order in BFO crystals is not homogeneous giving rise to poor magnetization and large leakage current due to cycloid spin structure [1]. To enhance magnetism and provide linear magnetoelectric interaction in BFO, it is necessary to destroy its cycloid spin structure.

Many research groups have tested composition of other pervoskite materials with BFO to enhance the ferroelectric and magnetic orderings [4]. An enhancement of magnetization in BiFeO3-BiCoO3 solid solution film has been observed at morphotropic phase boundary [4]. The effect of Mn-doping on crystal structure depends on whether BFO is in bulk or film form. The Mn-doped BFO in bulk ceramics form

remain in rhombohedral structure even up to 25 % content of Mn [5]. Therefore, it is essential to find the phase boundary line in BiFeO3-BiMnO3 films for improved multiferroic properties. In this paper, we report the morphotropic phase boundary in the (1-x)BiFeO3-xBiMnO3 system based on powder X-ray diffraction (XRD) studies.

EXPERIMENTS

The films were deposited onto the ultra cleaned glass substrate by sol-gel based spray pyrolysis method [6]. The BiFeO3 and 0.9BiFeO3-0.1BiMnO3 (BMFO) films were deposited at the substrate temperature of 600 K and were post annealed at the deposition temperature for 30 min. The films were thermally annealed at temperature of 825 K for 2h in a closed furnace. The x-ray powder diffraction data were obtained using an advanced Bruker D8 diffractometer with CuK� radiation. The crystal phase, morphology and particle size of films were characterized using a transmission electron microscope (TEM) at accelerating voltage of 200 kV.

RESULTS AND DISCUSSIONS

Figure 1 shows the XRD patterns of BFO and BFMO composite films deposited on glass substrate. A

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 46-47 (2013); doi: 10.1063/1.4790903

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polycrystalline rhombohedral perovskite structure with the space group R3c can be well indexed in the pattern of the pure BFO film [3]. In composite films, the splitting of the (012) peak around 220, the merging of the (104) and (110) peaks around 320, and the disappearance of the (006) peak around 400 characterized were observed, as shown in the inset Fig.1. This transition indicates that the rhombohedral structure of BFO film is modified and reduced toward the monoclinic or tetrahedral structure at 10 at.% of BMO, which may be the morphotropic phase boundary. The same behavior has been reported in BiFeO3:BiCoO3 composite and Mn-doped BFO films [4,5]. Meanwhile, all the peaks of the composite film shift towards lower diffraction angle comparing with these of pure BFO films, which indicates a large lattice distortion at morphotropic phase boundary. The average particle size has changed from 28.5 to 50.6 nm in BFMO samples as compared with BFO samples. The polycrystalline nature of the samples was revealed from the selected area electron diffraction (SAED) pattern (not shown).

FIGURE 1. The typical XRD pattern of the films with magnification patterns showing in insets for different 2� ranges of about (a) 220-230, (b) 310-330, and (c) 390-400.

Figure 3 displays the optical absorption spectrum of the BFO and BFMO thin films. It shows that the BFO film has a large optical absorption loss compared to BFMO film as a result of the electron hopping between Fe and O sites as well as between Fe sites with different valence states. We extract the direct band gap via a linear extrapolation of (�E)2 versus E plots to zero (inset Fig.3). The band gap in the BFMO film (Eg�2.55 eV) has significantly increased compared with that in the BFO film (Eg�2.32 eV). These values are in good agreement with the band gap with other experimental band gap values determined for BFO films [1,6]. Considered the inverse dependence of the band gap with respect to the lattice parameter (smaller the lattice parameter the larger the band gap), one can conclude that in-plane lattice

parameters for the BFMO film must be smaller than for the BFO film [10].

FIGURE 2. (a) The absorption coefficient, �(E) of BFO and BFMO films and (b) The plot of d�/dE as a function E. Inset in (a): direct band gap analysis of the films.

The d�/dE is plotted as a function of energy as shown in Fig.4 and different peaks were located around 1.9, 2.4 and 2.7 eV in the BFO films. Such peaks were also detected for BFO films deposited on SrTiO3 and glass substrates, and were confirmed by cathodoluminescent measurements [6]. These states are considered to be defect states most likely due to oxygen vacancies in the BFO films. Absence of the peaks in BFMO films show reduced oxygen vacancies and can be attributed to the presence of morphotropic phase boundary [4].

In conclusion, the morphotropic phase boundary has been observed in the BMFO solid solution films. The d�/dE plots show that oxygen vacancies substantially reduce at morphotropic phase boundary. The BFO film has a large optical absorption loss compared to BFMO film. The results of this work demonstrate that the electrical and optical properties of the films have strong influence at a morphotropic phase boundary. The reduction of optical absorption and increase in band gap in BFMO can be attributed to the morphotropic phase boundary.�

ACKNOWLEDGMENT

Annapu Reddy V. thanks MHRD for research fellowship.

REFERENCES

1. R. Ramesh, N.A. Spaldin, Nat. Mater. 6, 21 (2007). 2. R. Seshadri, N.A. Hill, Chem. Mater., 13, 2892 (2001). 3. V. Annapu Reddy, N.P. Path and R. Nath, J. Alloys

Compd. (2012), http://dx.doi.org/10.1016/j.jallcom.2012.07.098. 4. H. Naganuma, S. Yasui, Ken Nishida, Takashi Iijima, H.

Funakubo, and S. Okamura, J. Appl. Phys. 109, 07D917 (2011).

5. J. Z. Huang, Y. Shen, M. Li, and Ce-Wen Nan, J. Appl. Phys. 110, 094106 (2011).

6. V. Annapu Reddy, N.P. Path and R. Nath, AIP Advance 1 042140 (2011). �

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HCP to Omega Martensitic Phase Transformation Pathway in Pure Zr

Partha S. Ghosh*, A. Arya and G.K. Dey

Materials Science Division, Bhabha Atomic Research Centre, Mumbai-400085, India *Email: [email protected]

Abstract. We investigate a direct transformation mechanism for the pressure driven martensitic transformation in pure Zr as described by Silcock [2]. A systematic study of coupled atomic shuffles and strains evaluates transformation energy-landscape. The calculated change in enthalpy along this transformation path as a function of pressure shows decrease in enthalpy barrier with increase of pressure. We find the ab-initio nudged elastic band barriers at 0 K for this pathway is 68 meV/atom.

Keywords: hcp to omega transformation in Zr, Silcock pathway, martensitic transformation in Zr PACS: 64.70.Kb, 05.70.Fh, 81.30.Kf

INTRODUCTION

An important example of martensitic transformation is the pressure induced (hcp) (hexagonal) transformations in pure Zr and Zr rich alloys [1]. In one hand, these materials has significant technological implications in aerospace, medical, and nuclear fields due to its high strength, light weight, and corrosion resistance, on the other hand, formation of phase reduces toughness and ductility properties of these materials [1]. Thus there exists a substantial interest both from an industrial, applied and an academic point of view to develop accurate and effective methods to understand atomistic pathway for this martensitic phase transformation. In view of experimental work performed so far, there have been three suggestions for orientation relations (ORs) about the formation of omega structure ( ) from hcp structure ( ) in pure Zr. The first OR predicted by Silcock [2], which is a direct transformation pathway without any intermediate state and also involving significant atomic shuffle and relatively small strain, is (0001) �(11�20) and [11�20] �[0001] . The second structural model was predicted by Usikov and Zilbershtein [3] in which the transformation proceeds via the -phase. The OR's were derived by a lattice correspondence matrix which was the product of known and transformation matrices. Two omega variants were predicted by this procedure, (0001) �(01�11) ; [10�10] �[10�11] : variant I

(0001) �(11�20) ; [11�20] �[0001] : variant II. It is worth noting that the variant II is the same as that predicted by Silcock's model. Afterwards Rabinkin et al. [4] gave another diffusionless displacive model for

transformation and concluded that only three crystallographically equivalent variants corresponding to variant II were possible. In all experimental observations, the transformation pathways are always inferred from the orientation relationships (OR) between the parent and daughter phases. Such an approach may result in multiple transformation pathways for a given set of orientation relations, instate of indicating appropriate transformation pathway. Thus, hcp to omega transformation pathway in pure Zr is still not properly understood, despite several attempts. In this investigation we calculate the transformation landscape (as described by Silcock) as well as the enthalpy barrier as a function of pressure for pure Zr.

CALCULATION DETAILS

We calculate total energies for the transformation landscape using Vienna Ab Initio Simulation Package (VASP) with Plane wave based Projector Augmented Wave (PAW) method along with Generalized Gradient corrected Approximation (GGA) for exchange correlation functional. The energy barrier for Silcock transformation pathway was calculated using the nudged elastic band (NEB)

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 48-49 (2013); doi: 10.1063/1.4790904

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method. The NEB method generates a discretized pathway connecting the initial and final states (by generation of chain of images), and relaxes it to pass through the transition state to guarantee that the final pathway lies along the minimum energy pathway and produces the true energy barrier.

RESULTS AND DISCUSSION

The calculated equilibrium axial ratio (c/a), volume V0 (Å3/atom), zero pressure bulk modulus B0 (GPa) and pressure derivative of bulk modulus (B0') for and phase of Zr are given in Table 1. The calculated unit cell and cohesive parameters for these phases are in good agreement with experimental results.

TABLE 1. The equilibrium axial ratio (c/a), volume V0 (Å3/atom), zero pressure bulk modulus B0 (GPa) and pressure derivative of bulk modulus (B0'). The values given in brackets are experimental values [5]. Phase c/a V0 B0 B0'

1.598 (1.592)

23.59 (23.29)

94.6 (94.0)

3.39 (3.1)

0.618 (0.625)

23.31 (22.98)

95.0 (90.0)

3.57 (4.0)

Using these structural parameters for phase, a 12 atom orthorhombic (sp. gr. Pbcm) supercell ( a× c× a3 3 ) with atoms occupying 3 different 4(d) Wyckoff positions was made. Starting from that cell, structure was made by shuffle of 3 atoms (occupying (0001) plane) by 0.814 � along [11�20] , while the other 3 shuffle in opposite direction [�1�120] . This shuffle is accompanied by a strain exx = 0.05 and along [1�100] and eyy=-0.05 along [11�20] to produce a hexagonal cell with the correct c/a ratio. More details of the Silcock pathway can be found in [6]. The calculated transformation landscape is shown in

Fig. 1. FIGURE 1. The calculated transformation landscape for pure Zr at ambient condition where (0,0,0) and (1,1,0.005) correspond to hcp and omega phase, respectively.

Figure 2 shows the variation of enthalpy along the transformation path (Silcock pathway) as a function of pressure. Our calculation shows slightly lower in energy than at 0 GPa. As pressure increases, the enthalpy of relative to drops, and the pathway decrease their enthalpy barrier. We find ab-initio NEB barriers at 0K for this pathway is 68 meV/atom.

FIGURE 2. Enthalpy barrier as a function of pressure for the transformation pathway as described by Silcock.

CONCLUSIONS

We have presented a systematic pathway generation method for transformation in pure Zr as described by Silcock. This method enumerates possible range of strain and atomic shuffle to generate energy landscape of this transformation. According to our calculation, phase is slightly lower in energy than at 0 GPa. Also, the calculated equilibrium axial ratio (c/a), volume (V0), zero pressure bulk modulus (B0) and pressure derivative of bulk modulus (B0') for

and phase of Zr are in well agreement with experimental data. With increase of pressures, the enthalpy of phase relative to drops, and the pathway decrease enthalpy barrier. We find the ab-initio NEB barrier at 0 K for this pathway is 68 meV/atom.

REFERENCES

1. S.K. Sikka, Y.K. Vohra and R. Chidambaram, Prog. Mater. Sci. 27, 245 (1982).

2. Z. J.M. Silcock, Acta Metall. 6, 481 (1958). 3. M.P. Usikov and V.A. Zilbershtein, Phys. Stat. Solidi (a), 19, 53 (1973). 4. A, Robinkin, M, Talianker and O. Botsteirg Acta Metall.

29, 691 (1981). 5. Y. Zhao, J. Zhang, C. Pantea, J. Qian, L.L. Daemen, P.A. Rigg, R.S. Hixson, G.T. Gray, Y. Yang, L. Wang, Y. Wang, T. Uchida, Phys. Rev. B 71, 184119 (2005). 6. D. R. Trinkle, R. G. Hennig, S. G. Srinivasan, D. M. Hatch, M. D. Jones, H. T. Stokes, R. C. Albers and J.W. Wilkins, Phys. Rev. Lett. 91, 025701 (2003).

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Pressure Induced Phase Transition in NaNbO3

S. K. Mishra1*, R. Mittal1, S. L. Chaplot1, Thomas Hansen2

1Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India 2Institut Laue-Langevin, BP 156, 38042 Grenoble Cedex 9, France

*Email: [email protected]

We report high pressure powder neutron diffraction study in technologically important material sodium niobate using high-flux D20 neutron diffractometer at Institut Laue- Langevin, France. The measurements were carried out using Paris-Edinburgh cell upto 11 GPa in the pressure intervals of 1-2 GPa at 300 K. Rietveld refinement of the powder diffraction data revealed that diffraction patterns could be indexed using the orthorhombic structure (space group Pbcm) up to 6 GPa. Careful inspection of pressure dependence of diffraction data showed appearance and disappearance of certain superlattice reflections around 7 GPa. The new superlattice reflections that appear at 7 GPa, could be indexed by using an orthorhombic phase with space group Pbnm. We also observed that the response of the structural parameters with pressure is strongly anisotropic.

Keywords: Antiferro/Ferro, Neutron diffraction, Crystallographic aspects of phase transformationsPACS: 77.80.-e, 61.05.fm, 72.80.Ga

INTRODUCTION

Alkaline niobates based materials exhibit ultra-large piezoresponse comparable to PbZr1-xTixO3 (PZT). These materials have evoked considerable attention as the next generation eco-friendly lead-free piezoceramics [1-6]. One of the end members, NaNbO3 exhibits an unusual complex sequence of temperature and pressure driven structural phase transitions. The temperature induced phase transitions of NaNbO3 are extensively studied by various workers [4-6] (see Figure 1 of reference 4). The ground state of NaNbO3 is identified as ferroelectric (space group: R3C). On heating, it undergoes a series of antiferrodistortive phase transitions ranging from ferroelectric rhombohedral phase to the paraelectric cubic phase via intermediate antiferroelectric and paraelectric orthorhombic and tetragonal phases. The phase transitions are reported to be driven by zone centre and zone boundary phonon instabilities.

Using Raman scattering technique, Shiratori et al [6] have shown that NaNbO3, which stabilizes in an orthorhombic Pbcm structure at ambient pressure, undergoes successive transitions at around 2, 6, and 9 GPa respectively. Shen et al [5] also found that NaNbO3 undergoes a first-order phase transition at 7 GPa and another significant structural change at 12 GPa, which was prospected as a transition into the paraelectric phase. No attempt has so for been made to

examine the structure of these crystallographic phases using powder diffraction technique. The present experiments have been carried out to investigate the structures of the high pressure phases of NaNbO3 using neutron diffraction technique for the first time.

EXPERIMENTAL

Neutron powder diffraction experiments under pressure were performed at the high-flux D20 diffractometer with a Paris-Edinburgh device (P-E) in the Institut Laue- Langevin, France. The high resolution mode (take-off angle of 120º) was selected with a wavelength 1.3594 Å. The sample, mixed with Pb metal as the pressure manometer, was loaded into an encapsulated TiZr gasket filled with a 4:1 mixture of methanol-ethanol as a pressure medium before pressing in a P-E device. The structural refinements were performed using the Rietveld refinement program FULLPROF. In all the refinements, the background was defined by a sixth order polynomial in 2�. A Thompson-Cox-Hastings pseudo-Voigt with axial divergence asymmetry function was chosen to define the profile shape for the neutron diffraction peaks. All the refinements have used the data over the full angular range of 3�2�� 126 degree; although in various figures only a limited range is shown for clarity.

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 50-51 (2013); doi: 10.1063/1.4790905

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30 35 40 45 50 55

S2S1

0.1 GPa

S3

Inte

nsity

(arb

. uni

ts)

2��(degree)

6.4 GPa

NaNbO3 at 300 K

8.7 GPa

30 40 50

32 36 40

(Pbnm)

Inte

nsity

(arb

. uni

ts)

2��(degree)

P= 8.7 GPa(Pbcm)

RESULTS AND DISCUSSION

Figure 1 shows neutron diffraction patterns of NaNbO3 at selected pressure. At ambient condition, NaNbO3 has an antiferroelectric phase (Pbcm) at room temperature. The characteristic superlattice reflections around 2� =32o, 38o and 48o are one of the strongest antiferroelectric peaks, which are marked with arrows and labeled as S1, S2 and S3.

Fig. 1 Evolution of powder neutron diffraction of sodium niobate at selected pressure and 300K. S1, S2 and S3 corresponds to the superlattice reflections in the antiferroelectric structure.

The pressure dependence neutron data show significant changes with pressure especially in terms of shifting of various peaks. It is evident with increasing pressure (Fig. 1) the intensity of superlattice reflection centered at 2� =48o (label as S3), decreases and diminish followed by enhancement of the intensity of super lattice reflection at 2� =38o (label as S2). On the other hand, superlattice reflection appear at 2� =32o show abrupt change in position with pressure. Thus, disappearance and reappearance of superlattice reflections in powder neutron diffraction provide unambiguous evidence for structural phase transitions.

Detail Rietveld refinement of the powder diffraction data shows that diffraction patterns could be indexed using the orthorhombic structure (space group Pbcm) up to 6 GPa. The Rietveld refinements proceeded smoothly, revealing a monotonic decrease in lattice constant and cell volume with increasing pressure. The response of structural parameters to pressure is found to be strongly anisotropic [7]. Attempts to employ the same orthorhombic structural model in the refinements ~ 8 GPa (Fig. 2 (b)) proved unsatisfactory, and a progressive worsening of the quality of the Rietveld fits with increasing pressure was found. The most apparent signature of the subtle structural transformation that occurs at above 7 GPa is

the inability of orthorhombic structure (space group Pbcm) to account satisfactory for the superlattice peaks around 32 degree (see inset of figure 2).

In order to index additional superlattice reflection, we explored various possibilities and found that orthorhombic structure with space group Pbnm and cell dimensions �2��2�2 (with respect to elementary perovskite cell) indexed all the reflections as shown in fig. 2.

Fig. 2 Observed (circle) and calculated (continuous line), profiles obtained after the Rietveld refinement of NaNbO3 using orthorhombic Pbnm space groups at 8.7 GPa and 300 K. The arrow shows the accountability of superlattice reflection. Inset show non-accountabilities of the characteristic reflections using orthorhombic Pbcm space group.

Fitting the pressure versus volume data with a third-order Birch-Murnagham equation of state gives a bulk modulus B value of 157.5 � 1.0 GPa keeping B’=4 fixed, for the orthorhombic phase at room temperature. This experimental bulk modulus in NaNbO3 is fairly close to that in KNbO3 (B= 165 GPa) at room temperature. We have also determined averaged Nb-O bond length which shrinks almost continuously whereas a small jump of the Nb-O-Nb bond angle observed at 8 GPa. Above 8 GPa, the bond angle increases with increasing pressure which may associated with decreasing � bond contribution (details given elsewhere) [7].

REFERENCES

1. M. E. Lines and A. M. Glass, Principles and Application of Ferroelectrics and Related Materials Clarendon, Oxford, (1977).

2. Y. Saito et al, Nature (London) 423, 84 (2004); E. Cross, Nature (London) 432, 24 (2004).

3. Yu. I. Yuzyuk et al, Phys. Rev. B 69, 144105 (2004); ibid, J. Phys.: Condens. Matter 17, 4977 (2005).

4. S. K. Mishra, et al Phys. Rev B 76, 024110 (2007) and reference therein, ibid, Phys. Rev. B 83, 134105 (2011).

5. Z. X. Shen et al, J. Raman Spectrosc. 31, 439 (2000). 6. Y. Shiratori et al, J. Phys. Chem. C 112, 9610 (2008). 7. S. K. Mishra, et al (To be published).

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Liquid-vapor phase diagram of metals using EAM potential

Chandrani Bhattacharya

Theoretical Physics Division, Bhabha Atomic Research Centre, Mumbai-400094, India [email protected]

Abstract. Pair-wise additive potentials are not adequate to describe the properties of metallic systems since many body effects are completely ignored in that approximation. In this regard, the embedded atom method is more appropriate because, in addition to the pair interaction, the total energy includes an embedding energy which is the energy required to add an impurity atom to the host electron fluid. Thus EAM takes into account the many body effects to some extent. We use the Cai and Ye’s EAM potential to predict the liquid vapor phase diagram and critical constants of Aluminum and Copper within a perturbation theory approach. In this method, free energy of a fluid molecule, trapped in a cage formed by its nearest neighbors, is expanded about a hard sphere reference system. The first order correction term is calculated in terms of the zero temperature isotherm of the solid obtained using the EAM potential. Higher order correction terms are added to account for the deviation of the behavior of the real fluid from the reference hard sphere fluid.

Keywords: EAM potential, phase diagram, critical constant. PACS: 64.70.F-

INTRODUCTION

The critical properties and phase diagram of most of the metals other than mercury and some alkali metals have not been determined accurately in experiments. There is a wide spread in the values of critical temperatures reported in literature. This is primarily because of the high temperatures involved in these measurements as the critical temperature of most metals is in the range of eV. This necessitates development of accurate theoretical / simulation models to understand the behavior of metals in the low density, high temperature region. We use the embedded atom method (EAM) potential within a perturbation theory based approach developed by Kerley1 to determine the phase behavior of some metals. In this paper, we discuss briefly the model and some typical results.

FREE ENERGY MODEL

Kerley’s corrected rigid spheres (CRIS) model is a perturbation theory based approach. In this method, the free energy of the fluid molecule trapped in a cage formed by the nearest neighbours is expanded about a hard sphere reference system. The hard sphere reference system is chosen because the structure of

dense fluids is primarily governed by the excluded volume effects. The terms in the perturbation expansion are expressed in terms of the potential energy of a fluid molecule. Helmholtz free energy of the fluid of N atoms within a volume V is given by FFFF ideal �����

00 �� (1)

� � � � dRRRnRN

200 41 ��� �

� � )()1(3/2

SCss VE

VVf

VVfR

����

�������

Here, idealF is the free energy of the ideal gas. 0F is the free energy of hard spheres. The hard sphere diameter is determined so as to minimize the first three terms in Eq.(1). F� is a correction that arises because of the difference in the structure of the real fluid and the hard sphere fluid.

The first order correction 0

� is the average potential energy of the atom where the average is taken over the distribution )(0 Rn of nearest neighbors

of the hard spheres. 2/3RNVs � is the volume of the FCC solid and f is the fraction of free electrons per atom, which we obtain from the Thomas Fermi

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 52-53 (2013); doi: 10.1063/1.4790906

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model. One of the advantages of this method is that

0� is determined in terms of the zero temperature

isotherm )( sc VE , which we obtain using the EAM potential of Cai and Ye2. The EAM potential and consequently )( sc VE incorporates many body effects arising due to the presence of free electrons. This is important for metals because pair potentials alone cannot describe the interactions between the ion cores. This model was used earlier to predict the melting curve of some metals3. In that study, we also used the cell theory to calculate the free energy of the solid phase and the fluid-solid phase boundary.

RESULTS

The pressure vs. density curve obtained using the model was extended to very low densities. It was observed that (�P/�V)N,T > 0 in some region of the phase diagram. This is unphysical because compressibility becomes negative and so Maxwell’s construction is to be performed. A typical isotherm for Copper is plotted in figure 1.

0 2 4 6 8

0.00

0.04

0.08

0.12

0.16

0.20

Pres

sure

(Mba

r)

Density (g/cc)

FIGURE 1. 6000K isotherm of Copper. Red line is obtained after Maxwell’s construction. Results of phase diagrams of Al and Cu are given in Figure 2 and 3, respectively. The critical parameters for the two metals are reported in the Table.

0.0 0.5 1.0 1.5 2.04000

6000

8000

Tem

pera

ture

(K)

Density (g/cc)

Aluminum

FIGURE 2. Phase diagram of Aluminum.

0 2 4 64000

6000

8000

10000

Tem

pera

ture

(K)

Density (g/cc)

Copper

FIGURE 3. Phase diagram of Copper.

CONCLUSION

We obtained the phase diagram and critical constants for Al and Cu using EAM potential within the perturbation theory approach developed by Kerley. We find that the critical parameters lie within the range of values predicted by various theories and experiments reported in the literature.

ACKNOWLEDGMENTS

I am grateful to Dr. S. V. G. Menon for useful discussions during the course of this work.

TABLE 1. Critical parameters for Al and Cu (range of experimental data for critical temperatures given in brackets).

Element Critical temperature(K) Critical pressure(Mbar) Critical density(g/cc) Aluminum 8200 (5700-12100)4 0.0049(0.0046-0.0051)5 0.486 (0.28-0.66)5

Copper 8800 (5140-8700)6 0.0228(0.004-0.058)6 2.48 (1.8-2.6)6

REFERENCES

1. G. I. Kerley, J. Chem. Phys. 73, 469-487 (1980). 2. J. Cai and Y. Y. Ye., Phys. Rev B 184, 8398 (1996).

3. C. Bhattacharya, M. K. Srivastava, and S. V. G. Menon, Physica B 406, 4035 (2011).

4. D. Bhatt et al, JACS 128, 4224 (2006). 5. V. Mishra et al, Physica B 407, 2533 (2012). 6. T. Aleksandrov et al, Fl Phase Eq 287, 79 (2010).

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Role of Amphiphilic Molecule on Liquid Crystal Phases

Kaustabh Dan*, Madhusudan Roy and Alokmay Datta

Applied Material Science Division,Saha Institute of Nuclear Physics,1/AF Bidhannagar,Kolkata-700064 *Email: [email protected]

Abstract: We have studied the effect of an amphiphilic fatty acid, Stearic Acid (StA), on the phases, wetting and polarization properties of the liquid crystalline substance N-(4-Methoxybenzylidene)-4-butylaniline (MBBA), through Differential Scanning Calorimetry and Optical Polarization Microscopy. Metastable and mesophases disappear for a MBBA:StA = 1:5 mixture. This mixture wets Si(111) and dewets Si(100) surfaces while pure MBBA dewets both. Films of this mixture also show better polarization than the pure sample.�

Keywords: Phase Transition, Differential Scanning Calorimetry, Liquid Crystal-Amphiphile mixture, Wetting PACS: 64.70.pp, 61.30.pq

INTRODUCTION

Certain organic substances show a cascade of phase transitions, involving new phases, instead of a single transition from solid to liquid. Orientational and positional order along some local axis gives rise to these ‘liquid crystal’ (LC) phases [1].

LC phases appear is substances composed of molecular quadrupoles, where the competition between entropic and enthalpic forces gives rise to a rich variety of new phases with distinct physico-chemical properties. Both forces are small and introduction of small amounts of dopant can drastically change the balance of forces.

We present here some effects of an amphiphilic fatty acid, Stearic Acid (StA), as a dopant, on the phases of the liquid crystalline substance N-(4-Methoxybenzylidene)-4-butylaniline (MBBA), a rigid linear quadrupole, whereas StA contains a dipole in the carboxylic acid (COO-H+) group and a long non-polar hydrocarbon chain. EXPERIMENTAL DETAILS We have used both pure MBBA and 50 μLs of MBBA-StA mixtures dissolved in 500 μL carbon tetrachloride (CCl4) in the weight ratios MBBA: StA=1:2 and MBBA:StA=1:5. We have spin-coated 25 μL of the solutions on RCA cleaned Si (111) and Si (100) surfaces for 2 min at 3500 rpm speed. We have studied the films using a Carl Zeiss optical polarization microscope and 204 F1 Differential scanning Calorimeter.

RESULTS

Differential Scanning Calorimetry: The DSC measurements were carried out both in bulk and in films from -40°C to 70°C, at a heating or cooling rate of 10°C min-1. �H, �Cp and Tc correspond to enthalpy, change in Specific Heat and transition temperature, respectively.

-40 -20 0 20 40 60 80-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

Spec

ific

Pow

er A

bsor

ptio

n (m

W/m

g)

Temperature(oC)

Pure MBBA

a

b

c

d

�Figure 1: Differential Scanning Calorimetry data of pure MBBA The results for bulk phases of pure MBBA are consistent with literature [2]. It is clear from Table 2 that a number of intermediate phases are disappearing with increase in the StA fraction. Comparisons with

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 54-55 (2013); doi: 10.1063/1.4790907

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Table 1. �H, �Cp and Tc values for pure MBBA (bulk)

Phase Transition �H(Jg-1) �Cp(J(gK)-1) Tc(°C)

a:solid-metastable 3.709 0.272 -27.0

b:metastable-smectic 0.733 0.051 0.6

c:smectic-nematic 33.430 d:nematic-isotropic 0.116

4.573 20.0 0.032 40.0

-40 -20 0 20 40 60 80-1.5

-1.0

-0.5

0.0

0.5

1.0

MBBA:StA = 1:5

Spec

ific

Pow

er A

bsor

ptio

n (m

W/m

g)

temperature (0C)

MBBA:StA = 1:2

a

b

c

d

Figure 2: Differential Scanning Calorimetry data of MBBA:StA=1:2 and 1:5 deposited on Si 111

Table 2 �H, �Cp and Tc values for MBBA:StA=1:2 and 1:5

MBBA:StA Peak �H(Jg-1) �Cp(J(gK)-1) Tc(°C)

a 8.866 2.425 1.09 1:2 b 32.460 4.480 23.40 c 0.172 0.059 47.60 1:5 d 11.170 2.425 1.32

parameters of pure MBBA transitions let us temporarily assign ‘b’ and ‘c’ to smectic-nematic and nematic-isotropic transitions, respectively. Hence the smectic-nematic transition is shifted from 20°C to 23.4°C while the nematic-isotropic transition is shifted from 40°C to 47°C, i.e., the nematic phase is not strongly affected for the 1:2 mixture. However, for 1:5, both these transitions are absent till 70°C, while ‘a’ and ‘d’ appear to be a new transition in both mixtures, whose exact nature is to be ascertained. We have carried out some preliminary studies on the films of these mixtures. Optical Polarization Microscopy: Pure MBBA dewets both Si (111) and Si (100) surfaces (Figure 3(a) and (b)). In contrast, the Si (111) surface seems to be wetted (Figure 3(c)) while the Si (100) is dewetted (Figure 3(d)) by the mixture over a considerable range of composition. Also, the 1:5 mixtures show a higher degree of polarization than pure MBBA (Figure 4).

Figure 3: Spin coated thin film of MBBA on (a) Si (111) (b) Si (100) surface and MBBA: StA=1:5 on (c) Si (111) (d) Si (100) surface

Figure 4: Polarization micrographs of MBBA:StA=1:5 on (a) Si (100) and (c) Si (111) in the analyser 90° position, and on (c) Si (100) and (d) Si (111) in the cross analyser position. CONCLUSIONS From Differential Scanning Calorimetry and Optical Polarization Microscopy of MBBA-StA mixtures we find that, with increase in the StA fraction:1) metastable phases and mesophases disappear, 2) a new phase transition appears at low temperature, and 3) nematic-isotropic phase transition became stronger and smectic-nematic transition became weaker than pure MBBA, 4) Si (111) surface is wetted while Si (100) is dewetted, while pure MBBA dewets both, and 5) films become more polarized compared to pure bulk MBBA.

REFERENCES

1. P.G.De Gennes, Physics of Liquid Crystals 2. J.A. Janik et al, J. Physique C1 36, 159 (1975). 3. B.Van Roie,J.Leys,Physical Review E 72,041702 (2005) 4. L.Rosta and N.Kroo, Mol Cryst. Liq. Cryst 1987,Vol.144 pp.297-307

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Stabilisation of SrAl2O4 Hexagonal Phase at RT inZnO-SrAl2O4 Nanocomposite

V. P. Singha, S.B. Raib, H. Mishrac and Chandana Ratha*

a School of Materials Science and Technology, Indian Institute of Technology (B.H.U.), Varanasi, 221005, India b Department of Physics, Banaras Hindu University, Varanasi, 221005, India

c Department of Physics, MMV, Banaras Hindu University, Varanasi, 221005, India *Email: [email protected]

Abstract. In this article, we have reported hexagonal phase of SrAl2O4 (SAO) at room temperature by synthesizing ZnO-SAO nanocomposite which has been found to be difficult to achieve. Through combustion technique, we have made ZnO(20%)-SAO(80%) nanocomposite and revealed a good dispersion of ZnO in SAO matrix. A stable hexagonal phase at RT has been obtained in the composite sample calcined at 700 and 800 oC. Further, increasing the calcination temperature to 1000 and 1200oC, hexagonal phase transforms to monoclinic. From photoluminescence studies, we have observed an emission close to white light with changing the calcination temperature.

Keywords: ZnO, Nanocomposites, X-ray diffraction, Phase transformations, Photoluminescence.PACS: 81.05.Dz, 78.67.Sc, 61.05.cp, 61.50.Ks, 78.55.-m

INTRODUCTION

SrAl2O4(SAO) is well known to be one of the long persistent phosphorescent material. It has long been of great interests due to their important applications such as emergency route signs, identification markers etc. SAO displays two polymorphs: monoclinic and hexagonal. Below 650oC, it exhibits monoclinic space group, P21, and above that temperature, it turns out into a hexagonal phase, P6322. While monoclinic phase is a stable phase at room temperature, hexagonal phase is found to be a metastable phase at room temperature [1]. Literatures show that hexagonal phase can be stabilized by insertion of small amount of Ca[2], Ba[3], B[4] or excess Al or by annealing the monoclinic SAO at 950 oC[5]. Lots of efforts have been given to produce hexagonal SAO as the optical properties are very different in both phases. In this work, we demonstrate that hexagonal phase can be stabilized at RT by synthesizing composite of ZnO and SAO. Moreover, we annealed the sample at different temperatures and observed the structural and optical properties of these composites at RT.

EXPERIMENTAL

We have synthesized composite of ZnO(20%)-SAO(80%) by combustion technique and post

annealed them at various temperatures. During the synthesis we used nitrate precursors of analytical grade.� Urea is used as combustion fuel. In this synthesis technique the heat energy released by the redox exothermic reaction at a relative low ignition temperature between metal nitrates and urea is used. The process takes relatively a short time which enable to maintain the particles on the nanometer scale. The characterizations are carried out using TG-DTA, XRD, and Photoluminescence spectroscopy (PL).

RESULTS AND DISCUSSION

FIGURE 1. TGA-DTA curves of ZnO (20%)-SAO(80%) nano composite.

Differential thermal analysis (DTA) and thermogravimetry (TG) of composite sample is depicted in Fig.1. It can be revealed that an

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 56-57 (2013); doi: 10.1063/1.4790908

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endothermic reaction occurring at 134 oC is accompanied with an exothermic reaction at 155 oC. This clearly indicates that samples absorb heat for activating the combustion process and releases enormous amount of heat. After 200oC, two endothermic peaks are observed which could be due to the partial and full decomposition of aluminum nitrate. The result is supported by Capron et.al. [6]. TG shows 45 % of weight loss during the decomposition. Two more endothermic peaks associated with weight loss less than 10% are found between 550-600°C. While the first endothermic peak at 580 oC represents the decomposition of strontium nitrate and simultaneous formation of strontium aluminate, the later one at 613oC could be due to the monoclinic to hexagonal phase transformation [5].

FIGURE 2. X-ray diffraction pattern of ZnO(20%)-SAO(80%) nano composite calcined at different temperature

The Bragg peaks shown in Fig. 2 are found to be well matched with the structure of ZnO (JCPDS 89-1397) as well as with the hexagonal phase (P6322) of SAO (JCPDS 31-1336) in samples calcined at 700 and 800 oC. Further increasing calcination temperature to 1000 oC, the hexagonal (H) phase converts to monoclinic (P21) phase of SAO (JCPDS 00-034-0379). At 1200oC calcination temperature, while the phases of SAO and ZnO remain unchanged, the peak intensity is enhanced, indicating the growth of the particles. In most of the literatures monoclinic phase of SAO is found at room-temperature and hexagonal phase of SAO obtained by doping [3, 4]. It has been observed by Fukuda et.al. that room temperature monoclinic (P21) phase of SAO transforms directly to the hexagonal (P6322) at 650 oC. One may note that by adding ZnO in SAO, hexagonal phase of SAO can be stabilized and with changing the calcinations temperature we could able to change the phase of SAO from hexagonal to monoclinic. Moreover, we have established that using ZnO as filler in ZnO-SAO composite, ZnO facilitates the reaction and yields a pure phase of SAO without any undesired secondary phases. This has not been reported earlier.

Fig. 3 shows the photoluminescence spectra of composites at RT. A strong peak at 385 nm and a broad green emission peak in the range of 440 to

800nm are observed on excitation with 266nm wavelength. The green peak intensity has been compared between the composite calcined at different temperatures after normalizing the UV emission peak intensity. It is found that with increasing calcination temperature, the intensity of green emission also increases. Similar enhancement in green emission peak intensity for ZnO-GeO2 composite compared to pure ZnO have been reported by Djurisic et al. [7]. It seems that SAO are coated over the ZnO which is accompanied by large number of defects at the surfaces of ZnO. As a result, green emission enhances. The emission tending towards white light with increasing annealing temperature in ZnO-SAO composite, which is useful for white light emitting devices.

FIGURE 3. PL spectrum of ZnO(20%)-SAO(80%) nano composite calcined at different temperature.

CONCLUSION

We have stabilized room temperature hexagonal phase of SAO by synthesizing composite of ZnO and SAO. Increasing the calcination temperature from 800 to 1000oC, hexagonal phase transformed to monoclinic phase which is a stable phase of SAO at RT. We revealed an intense broad green emission which further amplified with increasing calcination temperature by exciting with 266nm uv light.

ACKNOWLEDGMENTS

V. P. Singh acknowledges CSIR, India for providing senior research fellowship.

REFERENCES

1. Fukuda et.al., J. Solid State Chem., 178 (2005) 2709 2. Prodjosantoso et.al., J. Solid State Chem. 168 (2002) 2293. Wu et.al., Physica B, 404 (2009) 2499 4. Jung et.al., Chem. Mater., 18 (2006), 2249 5. Douy et.al., J. Eu. Ceram. Soc., 23 (2003) 2075 6. Capron et.al., J. Am. Ceram. Soc., 85 [12] (2002) 3036 7. Djurisic et.al., Appl. Phys. Lett., 84 (2004), No. 14

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Effect Of Site Selective Ti Substitution On The Melting Point Of CuTi Alloys

Karabi Ghosh1 and Manoranjan Ghosh2

1Theoretical Physics Division, 2Technical Physics Division, Bhabha Atomic Research Centre, Mumbai – 400085 Corresponding author: [email protected] , Ph: 022-25593959

Abstract. In this work, the effect of site-selective substitution of Ti in Cu on the thermal stability of CuTi alloy has been investigated using classical molecular dynamics simulations with Embedded Atom Method potentials. For random substitution, the melting point decreases linearly with increase in Ti concentration. A non monotonous dependence is seen when Cu atoms at selective sites are replaced by Ti. For a particular doping concentration, the melting point shows a wide range of variation depending on the order of atomic arrangement and can be fine tuned by selecting the site of the substitution. The variations in melting point in different cases have been explained in terms of the peak height, width and position of their corresponding radial distribution functions.

Keywords: Molecular Dynamics, CuTi alloys, melting point, random doping, selective doping, Vegard’s law.PACS: 64.70.kd, 64.70.dj

INTRODUCTION

Conventionally, dopant concentration is varied to tailor the properties of an alloy material. In addition, for a fixed dopant concentration, change in position of the dopant atom in the host matrix facilitates to achieve finer control over the properties of an alloy. This site selective doping (SSD) has been realized experimentally and is also used to make an educated guess of the material properties.1 While majority of the reports on SSD are focused on the electronic properties, role of SSD on the thermal stability of the alloy is rarely investigated.

CuTi is a high strength alloy and widely used for direct brazing and joining of ceramics. Fabrication and processing of this alloy require a prior idea of its melting point (MP). The cell volume of CuTi is higher than its pure phase and predicts reduction in melting point as the Ti conc. increases. But, the phase diagram of CuTi alloy shows non-monotonous dependence of melting point on Ti conc.2 This anomaly in the melting curve can not be explained if only dopant concentration is held responsible, ignoring the spatial arrangements of Ti atoms. In this work, the effect of random and selective doping on the MP of CuTi has been investigated using classical molecular dynamic (MD) simulations. The variation in MP has been explained in terms of the characteristics of the Radial Distribution Function (RDF).3

RESULTS AND DISCUSSIONS

We employ the parallel MD simulation package DL_POLY4 together with the crystalline and molecular structure visualisation program XCrySDen. Using one phase method the MP of the CuTi systems is identified from sharp increase in atomic volume, diffusion coefficient and energy as temperature is varied. We have accounted for the interaction between atoms using the Embedded Atom Method (EAM) potential which incorporates the many-atom interactions neglected within the pair potential scheme. Structures of CuTi alloys having different Ti concentration have been generated by random or selective substitution of Ti in perfect fcc Cu supercells (Fig.1). For a fixed concentration, Ti can be introduced into Cu lattice in various ways to generate particular atomic arrangements.

FIGURE 1. Initial structure for random and selective doping of 25% Ti in fcc Cu supercell.

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 58-59 (2013); doi: 10.1063/1.4790909

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0.00 0.04 0.08 0.12

3.68

3.76

3.84

Latti

ce c

onst

ant o

f Cu-

Ti (Å

)

Ti conc. (at. wt. %)

Slope = 1.467 ± 0.026

FIGURE 2. Variation in lattice constant of the Cu-Ti alloy on varying the Ti concentration for random doping.

The melting temperature for Cu obtained from our simulations is 1340 K which agrees well with the experimental result of 1356K. For random doping, MP decreases linearly as Ti concentration increases (inset of Fig. 3). Since the atomic radius of Ti (2Å) is higher than that of Cu (1.57Å), cell volume increases when a Ti atom replaces a Cu atom. The increase in lattice parameter of the CuTi alloy is found to obey the empirical Vegard's law, which, for a given temperature, is a linear relation between lattice constant and concentration of the constituent elements (see Fig.2). As a result, the average distance between Cu atoms increases and the Cu-Cu bond strength decreases. This is clearly reflected in Fig.3 which shows the 0K RDF for the Cu-Cu bond. It is observed that the heights of the RDF peaks decrease, full widths at half maxima (FWHM) increase and the peak positions shift to the right on increasing Ti concentration. Decrease in RDF peak height is directly linked to the reduction in number of nearest neighbours. Also, increase in cell volume leads to shifting of RDF peak to the right. Thus for random doping, the average Cu-Cu bond strength and hence MP decreases linearly as dopant concentration increases. The systematic decrease in MP on changing the Ti concentration as observed for random doping is no longer seen in case of site selective substitution. Both dopant concentration and the site of substitution determine the MP of the alloy. For selective doping, MP decreases with Ti concentration up to 20% as in the case of random substitution (inset of Fig.4). Then the melting point increases for 25% Ti. As shown in Fig.4, up to 20 % Ti, the height of the first RDF peak decreases, become broader and position shifts to the right showing a loss in symmetry of the structure. But for 25% Ti, the first RDF peak becomes narrower and attains its maximum value. Its position does not shift further, indicating stronger Cu-Cu bonding compared to 20 % Ti. Therefore, high MP observed in case of 25 % selective doping can be understood in terms of the height, width and position of the RDF peak.

2.5 2.6 2.7 2.80

4

8

12

16

35%30%

25%20%

15%10%

RD

F

Distance Å

5%

0 10 20 301100

1200

1300

M.P

. (K)

Ti conc. (%)

FIGURE 3. Cu-Cu RDF peaks at 0K for random doping. Inset shows the M.P.s.

2.4 2.6 2.80

8

16

RD

F

Distance (Å)

Ti conc. 5% 10% 20% 25% 33.3% 50%

0 20 401000110012001300

M.P

. (K

)

Ti conc. (%)

FIGURE 4. Cu-Cu RDF peaks at 0K for selective doping. Inset shows the M.P.s.

Similarly, the low MP found in case of 33.33 % selective doping can be understood by the loss in Cu-Cu bond strength which is clearly evident from the corresponding short and broad RDF peak. Finally, peak height increases and becomes narrower for 50 % Ti which results in increase in MP.

In summary, the role of site-selective substitution of Ti in Cu on the melting point of CuTi alloy has been investigated. A direct link between the melting point and characteristics of the RDF peaks of the alloy has also been established.

REFERENCES

1. U. Bangert, A. Bleloch, M.H. Gass, A. Seepujak, J. van den Berg, Phys.Rev.B 81 245423 (2010).

2. W.A.Soffa and D.E.Laughin, Prog. Mater. Sci. 49 347 (2004).

3. A.B.Belonoshko et. al., Phys. Rev. B 79 220102(R) (2009).

4. W. Smith, T. R. Forester, I. T. Todorov and M. Lesley, DL_POLY 2 User manual, CCLRC, Daresbury Lab.

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Temperature Dependent Structural studies of Multiferroic La0.7Bi0.3CrO3 Perovskites

Aga Shahee, N. P. Lalla#

UGC-DAE Consortium for Scientific Research, University campus, Khandwa Road, Indore-452001 #[email protected]

Abstract. The temperature dependent structural studies on the polycrystalline La0.70Bi0.30CrO3 have been done using XRD and TEM. The results of the Reitveld refinement of XRD data and diffraction patterns of TEM confirm that it crystallizes in an orthorhombic structure with Pnma space-group and remains Pnma down to 80K. With decreasing temperature lattice parameters and cell volume decreases linearly with temperature.

Keywords: Perovskite, Multiferroic, XRD, TEM.PACS: 75.85.+t, 61.05.Cp, 68.37.Lp.

INTRODUCTION

During the past 10-12 years, a flurry of interest has grown towards the study of multiferroic materials.1 Multiferroics are compounds in which several ferroic orders coexist and can be simultaneously ferro-or antiferroelectric (FE-AFE) as well as ferro-or antiferromagnetic (FM-AFM). This multifunctional character opens the way towards its applications in storage media and represent a viable approach to the design of logic architectures.2

Bi doped LaCrO3 have recently been shown to be biferroic3 with small values of polarization similar to the YCrO3

4. We have also reported the occurrence of magnetoelectric coupling in La0.7Bi0.3CrO3

5. Since YCrO3 and similar materials have a centro-systematic (Pnma) crystal structure, to account for the occurrence of ferroelectric the concept of “local noncentrosymmetry” was proposed. Since it has been already reported that La0.7Bi0.3CrO3

5 has also centrosymmetric space-group (Pnma) at room temperature (RT), but at low-temperature3 structural studies, where system shows a strong ferroelectric character is still missing. Therefore details low-temperature structural study of this multiferroic sample is important.

EXPERMENTAL DETAILS

Perovskite oxides La0.7Bi0.3CrO3 were prepared by conventional solid-state reaction route using La2O3 (99.99%), Cr2O3 (99.99%) and Bi2O3 (99.99%). Since

Bi has high vapour pressure, the samples where prepared with 5% excess of Bi2O3 to maintain desired stoichiometry of the final product. After ~10 hours of thorough grinding, pellets of 14mm diameter and 3 mm thickness were made and sintered at 1250°C for 5-8 hours. Phase purity characterization and possible structural phase transition studies were done using powder x-ray diffraction (XRD) (D-max, Rigaku) and transmission electron microscopy (TEM) (TECNAI-G2-20) at room temperature and low temperatures down to 80K and 98K respectively. XRD was carried out using Cu-K� x-rays from a rotating anode generator operating at 40KV-200mA. The �-2� diffractometer was equipped with a graphite monochromator. For TEM observations thin samples were prepared following the standard technique using ion-milling (PIPS, Gatan). Liquid nitrogen based double-tilt (� ± 45o and � ±25o) TEM sample holder (Gatan 636MA) was used for imaging and diffraction studies at (RT) and 98K.

RESULTS AND DISSCUSION

Fig.1 (a,b) shows the Rietveld refined 350K and 80K XRD patterns of La0.70Bi0.30CrO3. The XRD patterns were refinement using the FULL PROOF-2K Rietveld refinement Program. Using this we were able to obtain accurate lattice parameters and Wyckoff positions. The space-group used for refinement was Pnma. All the observed peaks of 350K data were very nicely accounted by Pnma phase. We could not observe any unaccounted peak. This confirms the formation of single phase of La0.70Bi0.30CrO3 with orthorhombicaly

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 60-61 (2013); doi: 10.1063/1.4790910

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(a) (c)

<101> <010>

(b)

<010>

(a) (b)

distorted perovskite with Pnma space-group. The Temperature dependent XRD indicates that the system remains Pnma down to 80K. La0.70Bi0.30CrO3 has been observed to be biferroic in nature, with good PE hysterisys at 77K3 and the refinement of system by using a centrosymmetric space group indicates that the system has a long range centrosymetric crystal structural. Therefore the observed ferroelectricity may be thus due to presence of local non-centrosymmetric structure as predicted for YCrO3. Further the confirmation of Pnma space-group has done using TEM. Based on the refinement results a comparative graph of lattice parameters and unit cell volume was made; see fig.2. It can be seen that with decreasing temperature the lattice parameters and cell volume decrease linear.

20 40 60 80 100

-2000

0

2000

4000

6000

8000

10000

12000

14000

80K

2�

Iobs Ical Iobs-Ical Bragg Peaks

(b)

-2000

0

2000

4000

6000

8000

10000

12000

14000

Inte

nsity

(arb

.)

350K(a)

Fig.1 (a) 350K and (b) 80K Rietveld refined XRD patterns of La0.70Bi0.30CrO3.

50 100 150 200 250 300 3505.480

5.482

5.484

5.486

5.488

5.490

5.492

5.494

5.496

5.498

5.500

5.502

233.2

233.4

233.6

233.8

234.0

234.2

234.4

234.6

Vol

ume

(Ao3

)

Latti

ce P

aram

eter

s (A

o )

Temperature (K)

a

b/(2)1/2

c

V

Fig.2 The variation of lattice parameters and cell

volume of La0.70Bi0.30CrO3 with temperature from 350K down to 80K.

RT and 98K TEM was carried out on well characterized sample of La0.70Bi0.30CrO3. Fig.3 (a) shows an electron micrograph of densely packed

grains of sizes ~1μm. Fig.3 (b, c) represents selected area diffraction (SAD) patterns of La0.70Bi0.30CrO3 taken at RT. Through measurements it was confirmed that the SADs belong to the orthorhombic phase with lattice parameters a= 5.48Å, b= 7.76 Å & c= 5.49Å and correspond to (b) [010] and (c) [101] zones of the Pnma phase. This is in confirmation with Rietveld refined XRD results. Fig.4 (a) shows an electron micrograph of same grains taken at 98K. Fig.4 (b) represents SAD patterns of [010] zone taken at 98K. Thus low temperature TEM study further confirms that the system remains Pnma down to 98K.

Fig.3. Microstructure (a) and SAD patterns taken along (b) [010], and (c) [101] zones of the orthorhombic Pnma phase taken at 98K.

Fig.4. Microstructure (a) and SAD pattern taken along (b) [010] zones of the orthorhombic Pnma phase taken at 98K.

CONCLUSION

Based on above observations we conclude that the multiferroic La0.70Bi0.30CrO3 has a long range cento-symmetric structure with Pnma space-group down to 80K and the observed ferroelectricity in this system may be due to the presence on local non-centrosymmetry as proposed for YCrO3 and LuCrO3.

ACKNOWLEGEMENT

Aga Shahee would like to acknowledge CSIR-India

for financial support.

REFERENCES

1. W. Eerenstein, et al., Nature 442, 759 (2006). 2. N. Fujimura,et la., Appl. Phys. Lett. 69, 1011 (1996) 3. J. I. L. Chen, et al, J. Solid State chem. 177,4-5(2004). 4. C. R. Serrao et al. , Phys. Rev. B 72, 220101R (2005). 5. Aga Shahee, et al. AIP Conf. Proc. 1349, 1239 (2011);

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Dielectric and Ferroelectric Studies on Lead Free Piezoelectric KNN Ceramics

P Mahesh1, Ajeet Kumar2, A R James2, D Pamu1

1Department of Physics, Indian Institute of Technology Guwahati, Guwahati-39. 2 Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad-58.

Abstract. (K0.5Na0.5)NbO3 (KNN) ceramics are synthesized by solid state reaction method. The processing parameters such as calcination and sintering temperatures were optimized to get the stoichiometric KNN ceramics at lower processing temperatures. The effect of calination temperature on structural, microstructural and dielectric properties was investigated. The KNN ceramics calcined at 700oC and sintered at 950oC exhibited the best structural, microstructural, ferroelectric and dielectric properties. The dielectric studies revealed that that both the dielectric constant and tan� of KNN ceramics as function of temperature exhibited two sharp phase transitions indicating orthorhombic to tetragonal and ferroelectric tetragonal to paraelectric cubic phases. The prepared ceramics exhibited fine ferroelectric properties of remnant polarization and coercive field are 8.8�C/cm2 and 11.01KV/cm, respectively.

Keywords: Ferroelectric ceramics, Phase transition, dielectric properties, piezoelectrics. PACS: 77.22.Gm, 78.20.Ci, 77.80.B-.

INTRODUCTION

Lead-free piezoelectric materials have been studied due to the environmental and biological advantages and comparable piezoelectric properties to PZT [1]. Despite its excellent piezoelectric properties, one of the major disadvantages of PZT is potential lead volatility at higher temperatures. KNN is currently considered as a promising candidate of lead-free piezoelectric materials. KNN is a solid solution of ferroelectric KNbO3

and antiferroelectric [2]. KNN

possesses an orthorhombic structure at room temperature. However, densification of KNN ceramics is reported to be difficult at low temperatures. The present study demonstrates the preparation of KNN ceramics at low temperatures by reducing the initial particle sizes by mechanochemical synthesis process. The effect of calcination temperature on structural, microstructural, dielectric, and electrical properties of KNN ceramics have been studied systematically.

EXPERIMENTAL PROCEDURE

Samples of KNN ceramics were prepared by conventional solid-state reaction method from individual high purity powders (>99.99%) of K2CO3, Na2CO3, and Nb2O5. The starting materials were mixed in accordance with desired stoichiometry of the

KNN ceramics. A planetary ball mill (Fritsch GmbH, Germany) was used to mix these powders. The powders were mixed with proponol and the mixed powders were dried and calcined at different temperatures (600oC, 700oC, 800oC and 900oC) for five hours. The calcined powders again grounded for 5 hours and are uniaxially pressed into pellets. These pellets were sintered at temperature 950 oC for 5 h. For the electrical measurements, a silver paste was used for the electrical contacts. The samples were poled in a silicon oil bath at 150oC by applying the electric field 20kV/cm during 15 min. The phase purity of the calcined powders and the sintered pellets was identified by X-Ray Diffractometer (Bruker D8). The dielectric constant and dielectric loss were measured using LCR meter (Wayne Kerr Electronics Pvt. Ltd., Model 1J43100). A PID temperature controller is used to control the temperature of the heating assembly up to 500oC. Microstructure was evaluated on polished samples by using SEM (LEO-1430PV). P-E hysteresis loops were determined by the aixACCT systems Germany, at 25Hz near room temperature.

RESULTS AND DISCUSSIONS

Fig. 1(a) shows the XRD patterns of the KNN ceramics, calcined at different temperatures and sintered at 950oC for 5 hours. It is observed that all the

Solid State Physics (India) Vol. 57 (2012)AIP Conf. Proc. 1512, 62-63 (2013); doi: 10.1063/1.4790911

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samples exhibited single orthorhombic phase except for the sample calcined at 600oC. It is also observed that as the calcination temperature increases the peaks are broadened and peak position shifted to lower side. The crystallite sizes of the KNN ceramics are in the range of 60 nm to 20nm. Chang et al [3] reported the single phase for the KNN ceramics at 850oC. This shows the importance of mixing initial reagents by high energy milling in reducing the initial particle size and uniform mixing for the low temperature synthesis of KNN ceramics. The smaller particle sizes would accelerate the chemical reaction between the initial reagents also reduces the reaction temperature. The sample calcined at 700oC exhibited complete phase formation and exhibited best microstructural, dielectric and ferroelectric properties and hence the data related to this sample was presented in this study. Fig.1 (b) shows the SEM micrograph of the KNN sample sintered at 950oC for 5h. It shows the grains are in rectangular shape with dense packing. The average grain size is found to be 1.5-2μm. The relative densities of the KNN ceramics were measured by Archimedes method and were in the range of 80-90.4%. The sample calcined at 700oC found exhibit the maximum density of 4.077g/cc which is 90.4% of the theoretical density (4.51g/cc).

20 30 40 50 60

700oC

2� (Degrees)

Inte

nsity

(arb

. Uni

ts)

800oC

(220

)(0

02)

(112

)

900oC(110

) (020

)

(021

)

(001

) (200

) (111

)

(221

)

(311

)(0

22)

(a)

FIGURE 1. (a) XRD patterns of KNN ceramics calcined at different temperatures and (b) Microstructure calcined at 700oC and sintered at 950oC for 5 h.

The hysteresis loop (P-E) of the KNN sample is shown in Fig 2(a). It is found that the values of Pr and coercive field were 8.787μC/cm2 and 11.01kV/cm, respectively. All the samples showed saturation polarization (Ps) when an electric field of 20kV/cm is applied. The temperature dependence of dielectric constant (�r) and tan� of KNN ceramics calcined at 700oC, sintered at 950oC for 5 h and measured at different frequencies, is shown in Fig. 2(b). It is observed that two sharp phase transitions are observed both in �r and tan� values around 165oC and 335oC each respectively representing the orthorhombic to tetragonal and ferroelectric tetragonal to paraelectric cubic phase transitions. Ferroelectric to paraelectric phase transition occur due to the lowest frequency soft mode [4] tends to zero, this leads the maximum

dielectric constant at Tc, which can be explained by LST relation.

-20 -15 -10 -5 0 5 10 15 20-12

-8

-4

0

4

8

12(a)

Pola

riza

tion

(�C

/cm

2 )

Electric field (kV/cm)50 100 150 200 250 300 350 400 450

200

400

600

800

1000

1200

50 100 150 200 250 300 350 400 4500.0

1.0x10-4

2.0x10-4

3.0x10-4

4.0x10-4

5.0x10-4

6.0x10-4

7.0x10-4

Die

lect

ric

cons

tant

(�r)

Temperature(oC)

Tan�

Temperature(oC)

measured 0.5 MHz measured 0.75 MHz measured 1 MHz

(b)

FIGURE 2. (a) P-E loop and (b) Temperature dependent �r and tan� (inset) values as function of frequency of the KNN

ceramics calcined at 700oC and sintered at 950oC for 5 h. The transition temperature does not shift to higher temperatures when the frequency is increased; it implies that the sample does not exhibit a relaxor behavior. The tan� also shows similar kind of transition peaks to �r. The tan� increases with the temperature due to the increase in the mobility of ions in the sample. The obtained �r and tan� of KNN ceramics were in the range of 340-1190 and 5.9×10-5-5.3×10-4, respectively. The decrease in �r value with increase in frequency can be attributed to the decrease in polarization. At low frequencies, all the polarization mechanism respond easily to the time varying electric field but as the frequency of the electric field increases different polarization contributions filters out, as a result, the net polarization of the material decreases which leads to the decrease in the value of �r.

CONCLUSIONS

In conclusion, KNN ceramics are prepared by solid state reaction method. The structural and dielectric properties of KNN ceramics showed a profound dependence on processing parameters. The Phase transitions from orthorhombic to tetragonal (165oC) and ferroelectric tetragonal to paraelectric cubic (335oC) phase transitions are observed in the present study.

ACKNOWLEDGMENTS

Authors acknowledge BRNS for the financial support.

REFERENCES

1. E. Cross, Nature 432 24-25 (2004). 2. Haibo Zhang, Shenglin Jiang, and Koji Kajiyoshi, J.

Am. Ceram. Soc., 93 1957–1964 (2010). 3. Y. Chang, Z. Yang, X. Chao, R. Zhang, X. Li, Mater.

Lett., 61 165-169 (2007). 4. L. Egerton and M. Dillon, J. Am. Ceram. Soc. 42 438-

442 (1959).

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