Introduction to the difraction analysis and SANS method

Introduction to the difraction analysis and

SANS methodStudents:

Dana-Maria GHITA (Univ. of Craiova, Romania) Nicoleta-Madalina GIURGEA (Univ. of Bucharest, Romania) Andreea OPREA (Univ. of Bucharest, Romania) Claudia-Teodora TEODORESCU-SOARE (Univ. of Jassy, Romania)

Project Coordinators:

Dr. M. L. CRAUS (FLNP) Dr. A. I. KUKLIN (FLNP)

JINR Summer Student Practice 5-25 July 2010

Part 1:Corelations between

structure and transport caracteristics

of manganites with Cr impurities (La0.54Ho0.11Sr0.35)

(Mn1-xCrx)O3

Outline

Work done within the Project Overview Results Conclusions

Work Done Within the Project

Manganite samples with the general structure La0.54Ho0.11Sr0.35Mn1-xCrxO3 have been studied using FullProf Suite code for existing data at (x = 0.05; 0.10; 0.15; 0.20).

The goal of investigation was to estimate qualitatively :

(1) the variation of the lattice constant values in terms of Cr impurity concentration

(2) microstrain and crystallite average size dependence on the Cr concentration.

Outline

Work done within the Project

Overview Results Conclusions

Overview

The samples: La0.54Ho0.11Sr0.35Mn1-xCrxO3 manganites were prepared by sol-gel

method using oxides and acetates and sintered in air at 1200

C for 15 h.

It is known:The samples show perovskite phases, with orthorhombic

structure (Space Group – P n m a). ABO3 perovskito-manganites determine the charge transport behavior and complex magnetic and crystalline structures.

X-ray data for samples (with different Cr concentrations) mentioned in our report was obtained with Hubber-Guinier diffractometer by using Cr Kα1 radiation and was handled using FullProf Suite code.

Unit cell of manganite La0.54Ho0.11Sr0.35Mn1-xCrxO3

Features:

- Distorted Perovskite

- Orthorhombic space group: Pnma #62

- Primitive lattice (P)

- Glide plane (n) perpendicular to a axis

- Mirror plane (m) perpendicular to b axis

- Glide plane (a) perpendicular to c axis

FullProf Main Features The program has been mainly developed for Rietveld analysis

(structure profile refinement) of neutron (nuclear and magnetic scattering) or X-ray powder diffraction data collected at constant or variable step in scattering angle 2θ

• X-ray diffraction data: laboratory and synchrotron sources.

• Neutron diffraction data: Constant Wavelength (CW) and Time of Flight (TOF).

• The scattering variable may be 2θ in degrees, TOF in microseconds and Energy in KeV.

• Background: fixed, refinable, adaptable, or with Fourier filtering.

• Choice of peak shape for each phase: Gaussian, Lorentzian, modified Lorentzians, pseudo-Voigt, Pearson-VII, Thompson-Cox-Hastings (TCH) pseudo-Voigt, numerical, split pseudo-Voigt, convolution of a double exponential with a TCH pseudo-Voigt for TOF.

• Multi-phase (up to 16 phases).

• Absorption correction for a different geometries. Micro-absorption correction for Bragg-Brentano set-up.

free program http://www.ill.eu/sites/fullprof/

FullProf Main Features • Choice between automatic generation of hkl and/or symmetry operators

and file given by user.

• Magnetic structure refinement (crystallographic and spherical representation of the magnetic moments).

• hkl-dependence of the position shifts of Bragg reflections for special kind of defects.

• Profile Matching. The full profile can be adjusted without prior knowledge of the structure (needs only good starting cell and profile parameters).

• Quantitative analysis without need of structure factor calculations.

• Chemical (distances and angles) and magnetic (magnetic moments) slack constraints. They can be generated automatically by the program.

• The instrumental resolution function (Voigt function) may be supplied in a file. A microstructural analysis is then performed.

• Neutron (or X-rays) powder patterns can be mixed with integrated intensities of X-rays (or neutron) from single crystal or powder data.

• Full Multi-pattern capabilities. The user may mix several powder diffraction patterns (eventually heterogeneous: X-rays, TOF neutrons, etc.) with total control of the weighting scheme.

Outline

Work done within the Project Overview

Results Conclusions

Observed and calculated difractograms of

La0.54Ho0.11Sr0.35Mn0.95Cr0.05O3 (FullProf method)

Observed and calculated difractograms of

La0.54Ho0.11Sr0.35Mn0.90Cr0.10O3 (FullProf method)

Observed and calculated difractograms of

La0.54Ho0.11Sr0.35Mn0.85Cr0.15O3 (FullProf method)

Observed and calculated difractograms of

La0.54Ho0.11Sr0.35Mn0.80Cr0.20O3 (FullProf method)

Variation of the lattice constants and the unit cell volume (a,b,c,V) vs. Cr

concentration x

x a(Å) b(Å) c(Å) V(Å3)

0.05 5.4229 7.6628 5.4038 224.553

0.10 5.3786 7.5831 5.3924 219.937

0.15 5.3793 7.5922 5.3865 219.989

0.20 5.3767 7.5946 5.3823 219.780

Variation of the microstrain Ɛ and of the apparent size of the crystallite vs. Cr

concentration x

x Ɛ D (Å)

0.05 0.0289579 467.86

0.10 0.0317542 423.55

0.15 0.0265669 712.69

0.20 0.0222624 601.97

Outline

Work done within the Project Overview Results

Conclusions

Conclusions to Part 1

Lattice constants a and c decrease decrease monotonicallymonotonically, while b and unit cell volume V vary non-monotonicallyvary non-monotonically with the Cr (chrome) concentration.

The microstrain shows a maximummaximum, while the average size of crystallites shows non-monotonicnon-monotonic variation with Cr concentration .

Part 2 : SANS - Introduction•Small angle neuton scattering is a method of analisys used in research for the determination of the structures and parameters of different solid samples.

•The measured magnitude in a small angle scattering experiment is the intensity as a function of the momentum transfer Q=4π/λ sinΘ (scattering vector).

• SANS techniques:

-The pin-hole SANS covers the conventional range of 1 to 100nm. This range is exptended by the focusing SANS with either mirrors or lenses up to 1000nm.

-The double crystal (Bonse Hart) diffractometer reaches length scales in the μm range.

Information which can be obtained by SANS

• Sizes, spatial correlations and shapes of particles, aglomerates, pores and fractals in crystalline and amorphous states, as well as in solutions on a length scale ranging from 1 nm up to several hundred nanometers

• Phase transitions

• Degree of polydispersity

• Aggregation numbers

• Molecular weight

• Geometric peculiarities

Special methods

Contrast Variation Method– Determination of object density – Investigation of system homogeneity

Label Method– Analysis of density distribution inside the object under study

1 – two reflectors;2 – zone of reactor with

moderator;3 – chopper;

4 – first collimator;5 – vacuum tube;

6 – second collimator;7 – thermostate;

8 – samples table;9 – Vn-standard;

10 – ring-wire detector; 11 – position-sensitive

detector "Volga";12 – direct beam

detector.

YUMO-Frank Laboratory of Neutron Physics, Joint Institute of Nuclear Physics, Dubna, Russia

SAXS and SANS comparison

Commons: - elastic

- coherent

- magnetic scattering

- nuclear

Differences : SAXS - big scattering angle

- q range = 0.8 ÷1 Å-1

SANS - small scattering angle

- q range= 0.001 ÷1 Å-1

Conclusions to Part 2

• SANS is a powerful method for the investigation of sizes, shapes and density of particles in the range of: 20 ÷ 10 000Å.

• The neutron measurements also enable the determination of magnetic correlations inside samples.

• Contrast variation methods in the SANS framework allow nuclear and magnetic density estimates.

• Etc.

References• “Transport phenomena in La0.54Ho0.11Sr0.35Mn1-xCuxO3

manganites” Mihail-Liviu Craus1,2, Nicoleta Cornei 3, Ahmed Islamov2 and Vasyl M. Garamus4

• http://www.ill.eu/sites/fullprof/

• www.flnr.jinr.ru

• Neutron Scattering, Thomas Brϋckel, Gernot Heger, Dieter Richter and Reiner Zorn, RWTH Aachen, University of Mϋnster

• Perovskiti Magnetorezistivi: sinteza, proprietati si aplicatii, Mihail-Liviu Craus, Nicoleta Cornei, Mihai Lozovan, Viorel Dobrea, Iassy:Alfa, 2008

• An introduction to the program FullProf, Juan Rodríguez-Carvajal, Laboratoire Léon Brillouin (CEA-CNRS), CEA/Saclay, 91191 Gif sur Yvette Cedex, FRANCE

Acknowledgments

• We are indebted to the Project leaders for their guidance &

patience.

• Thanks to the Direction and staff of UC for the nice

organization of the summer student practice

• Thanks to Prof. Dr. Gh. ADAM and Dr. S. ADAM for advice

during the Summer practice

• Thanks to Dr. O. CULICOV for the Reactor tour

• Also thanks to Phd. Student R. ERHAN for good advices during

the Summer practice

Thank You for Attention!!

Thank you for attention!!