EXI'ERIMENTAL TECHNIQUES 2.1, INTRODUCTION 2.2. COMPONENTS OF SUPERIONIC CONDU(JI1NC CUSSES 2.2.1. Class Fomer 1.2.2. Glass Mcdifir 2.2.3. Ihpant Salt 2.3. PREPARATION TECHNIQUES OF GIA-SS 2.3.1. Melt quench Rwrss 2.3.2. Sol-gel Recess 2.3.2.a. Colloidal Prorrss 2.3.2.b. Alkaxide Roccss 2.4. SRUCTURAL CtUUWCTERIZATION 2.4.1. X-ray DiIfraction (XRD) 2.4.2. Fowkr Transfom InfraRed Specmscopy (FITR) 2.4.3. Diatrtntlai !%mning Calori~net~ ID%) 2.5. TRANSPORT STUDIES 2.5.1. Various Factors Affecting the Conductivity -
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EXI'ERIMENTAL TECHNIQUES
2.1, INTRODUCTION
2.2. COMPONENTS OF SUPERIONIC CONDU(JI1NC CUSSES
2.2.1. Class Fomer
1.2.2. Glass M c d i f i r
2.2.3. Ihpant Salt
2.3. PREPARATION TECHNIQUES OF GIA-SS
2.3.1. Melt quench Rwrss
2.3.2. Sol-gel Recess
2.3.2.a. Colloidal Prorrss
2.3.2.b. Alkaxide Roccss
2.4. SRUCTURAL CtUUWCTERIZATION
2.4.1. X-ray DiIfraction (XRD)
2.4.2. Fowkr Transfom InfraRed Specmscopy (FITR)
2.4.3. Diatrtntlai !%mning C a l o r i ~ n e t ~ ID%)
2.5. TRANSPORT STUDIES
2.5.1. Various Factors Affecting the Conductivity -
In recmt times, a number of new glassy materials with lugh ionic
conductivity havc taken up the name superionic m n d t m r s (SICS) and find
various potential applications in the solid state ionic devices 11, 21. The
superionic mnduaing glasses possess many inherent properties like the
selection of wide range of composition, isotropic, no grain boundary eBect, thin
film formation, fmsibil~ty of shaping & more of unreactivity and these materials
a n be synthesitcd through Vwous prrparative techniques 13 - 61. This chapter
bridly describes about the synthesis of superionic conductmg glassy materials by
sol-gel & meltquench teduuques and the chaacterization by ditferent
experimental methods like XRD. FTIR, DSC & impedancz spectroscopy [ l - 41.
Ghss is a matenal that comes under the family of nonaystallme solids.
Gbss posscssts propenies like short-range penodic order of the constituent
atoms WJc of penodiaty), do not have a determined melting point, also do not
ckavc in prefermi dmct~ons and even good elasticity nature in the form of fibers.
The tenn glass means in general, the fusion product of inorganic matuials
obtained by coohng to a ngrd condition without forming a uystalline phase, and
IS chamcterkd' by the ghss ransition rempcratun 1I;1 13 - 61. At glass
transitiosl temperatun, sdid amorphous phase exhibits an abrupt change in first
derivative d thamodynamics pmpcmes like t h e m eqmsivity, heat capacity
etc. The prrpetation of amorphous matuials can be regarded as the
addition of aocess k cnagy in some manna to the aystalline polymorph.
OLens b cPn8ncd to thost mataials, which can be obtained in a rcpmdua'blc
state (mn a&r tCRlperaNIt qchg), since the mamial can be in a state of
iritanal qunfbrkun above the ~ ~ E S S transition. Ghscs are also known b k
v i m wtids. T b m j d y , all mataids can k made into glasses, if mdad
fast enough. Glasses p r e p a d need not be onIy horn inorganic compounds but
even it can be pnpartd from cane sugar, known as bllipops, which form rigid
block shape and cotton candy, arc flexible fiber 161.
The chemical composition of any glass can be acprssed in three major
types of constituents in different proportions as a) network former b) network
modifier and c) dopant salt 15 - 141. The formula for three component glassy
systems can be expressed as
Thesc t h m terms in the basic systems art defmed as
quench, Sal -Gel procrss, etc. Of the abate mentioned techniques, the
wnvcntional, Melt quench method, and unconventional, Sol-gel process art the
hVO technqucs manly locuscd in the p m n t investigation.
The melt quench precess is a wnvcntio* method to prepare
arnorphous/glass, by su&&~tly fast cooling the molten form of the material. In
@naal, the quenching rates vary from 103 to 1109 Ks-I and above, depending
Upon the type of material and on the preparative tshniqus fobwed for the
synthcafs. Henct, the fixmation is based on its kinetic phcnamuutn. 'Ilu
~ r a t c a d e t a m i n e d i n t h c p l t p e r a ~ o l s ~ m e ~ t h t g l a s a e s , E O P 4 I
cxampk, glass-former such as &Oh fonn a glass under a slow c m h g rate lKsl,
whaeas metallic glace*, require very high rats of cooling. Duwez in 1959 6rst
demonatrated that the mhng rate in excess of 106 Ksl could be obtained using
chill-blocks of copper to quench into thin films of the melts. Kltment et a1 in
1%0 pnpand morphous metal Au~~Sim through melt ~ u m c h i n g process by
'rimp smasher', i.e., small droplets of l~quid on a Cu sheet yielded lo5 to 106 Ksl
cmling ratc:. Using melt spinrung and melt extradion techniques, the cooling
rate of the orda 106 - 1P Ks was achieved. Fig. 2.2 shows some of the diffexent
methods of prtparing glass. Table 2.1 gives the techniques used in quenchng
p rmsscs and their charaaaistic rates of cooling 131.
Table 2.1 Quenching techniques and their characteristic rates of cookg - - -- ----- -
Technique 1 coollngrate (Ks-1) i .Ann- L. teksaope mirror optical @ass' o*'glass'
Air quenching
Liquid quenchmg
Chill- block Splatcoobng
I j S 109 I Evaporation, sputtering
In the pnscnt investgation, the tihum vanadophosphate - VzOs - Pas] (LVq systan is preClerrd by the melt quench method.
method wps adapted in the synthtsis of and caamic
rnatakb~ in mid-1800 (16 - 181. ~aweva, the pion- and extamkc work by 42
Rg. 2.2. Schanatjc -tations ofdiEaent methods for the preparation of glasses 4 sbw coolurg Q quenching c) !win roller quenching d) thermal evaporation
Roy et a1 brought out the ml-gel technology as a frontier area of mamiah
research 119 - '221. The ml-gel pmxm can be demibed as chemical technique of
simpliuty and eflcctiveness to synthcske different type of inorganic and orgsnio
inorganic hybnd mataiab, which can be used in solid state devices. Wide ranges
of new and known materials containing d e components4ave been s u w
prcpand in reant time 16, 23 & 241. Scheme 2.3 shows the csmmtials of the gmcric sol-gel pmms and it is used to prrpare various forms of glasses, ceramics
and noncrystalline ceramics. Sol-gel technque foUows the route-line of
h.ydrolysls and potymmation to form amorphous/aystalline material at bw
temperature pnxzsslng in solution state (23 - 251. The process allows to design
h e morphology of electrochemical materials by which the propaties of s u b
and interface can be mdifml. The sol-gel process is based on two different
wutcs to synthcsLs crystalline and amorphous/glassy material via gel by a)
Hydro* and condensation of akoxides form a polymeric network product
known to be sol. The water and alcohol as the by-product of reaction remains in
the porn of the network.
The obtained sol is a low-viscosity liquid, which can be casted into a mold.
The rnokl must bc free of adhesion of the gel.
Ckhtion is the msi t ion fmrn a solution to a solid, involves condensed
specks Lnkd @ether to become thm-dunensional network atended
thmughout the iquid volume. A sudden increase in viscosity results in gelation
of the solution to fonn solid object rsult. The degne of gelation can be cantmIled
by the propa ampunt d water addition. Other parameters also found empmcally
lo &at the @tion proass m solvent, ternperaturr, complex ligands and pH
value. The a01 to gel transition can be monitored by various techniques Eke gas
chmmetqmphy (GC), nuclear mapetic resonanu (WRj, small angle X-ray
scattuing (SAXS) and viscosity measurements 1251.
Aging b a pdrod of time d a gel to be maintained at a particular
tanpaaaut, durlng wbich the &ngm that occur are cete&d aa 47
polymcritation, qmmis, cmaenhg and phase transformation. On aging polycondcnsation continues to occur within the gel network as long as
naghboring silanols an close enough to mct. Synmsis is the spontaneous
shrinkage of the gel resulhng expulsion of liquid from the pores along with the
localized solution. Coarserung is the irreversible d m kt surface area through
dissolution and rtprecipitation of the gel network that result in the incresse of the
thickness of perticle necks and decmscs the porosity. Thus, on aging, the
smngth of the gel increases to mist crackmg during drymg.
Dunng the drying proass, the liquids in the capillary pore network are
rcrnovrd. The pressure that is dwrloped during the proctss is proportional to the
reduced intcrladal a m in the gel, which in turn deurases the volume of the gel,
which is equal to the volume of the lquid lost by evaporation. Due to this
maximum pnssure generated, gel remained shrunken and cracked or become
powder.
The rrmrval of surface elements Wrr H and R res@velv from the Si-OH
(silanol) and Si-OR bonds from the pore network result in a chemical& stable
ultrapomussdid
The last matmcnt in the processs of gel is known as dmsi6cation. By
heating the paws gel at tcrnptum, the ports can be eliminated and the
d m d k d can k obtained, e.g. fused quartz or fused silica The
denrdecarbn m n m : depnds an the gel microstructure that is detamined
by the condWoM of gehabn, aging and dvQ. On the prooeps, the driEd gd 48
shrinks and converts to a densilied oxide glass. The controlled heat-treated gels
lo beer tcrnprratum form glassy materials can be monitored through XRD,
I'CA, NMR, FI1R. DSC, etc.
C~hsscs, synthsi;r*td thmugh thc sol-gel proms, can be obtained in
tlillemnt l o r n with particular chardcteristics, are given in the table 2.2, which
,m used for various applications (25,261.
Hetter purity and homgcneity
Lawer tcmptraturt of preparation, save energy, minimize evaporation losses,
;ninimizc air pollution, no mction with containers, by pass phase separation S
etc.
New non-a)stallme soMs outside the range of normal glasses formation
New c q a a l h e pheses hrn new nonaystalline solids
Rettcr glass paaiucts born speaaJ properties of gels
HI@ cost of raw mat&
Lageshrinkast~uringproassing Rceidual fine miaomty, midual h-ydmql and residual carbon
Health hezards dorgBnic solutions
~wprocessinetfmc
Ditficuhy In produdnglatgc pims.
Forms
1 Chemical variability, high homogeneity, 1 stable oxide coa- cermets, simple
I p- I I Drawable from solution, low temperaturr,
I chermcal variability, purity, optical fib=,
j ceramics e.g. M ~ ~ ~ - & O J - S ~ O Z I
I 1 Chermcal vanabibty, monoslzed powders of lnarrow htribuhon, spherical, production temperature of s~ntered bodies
low i j Monohthlo, rods, rubes , low pmpssmg temperature m rnuitmmpo- 1 I nent oxides, punty
t i o h s p h m I S p d cise for nuclear fuels
I Glasses
I
I Supenonlr mnductors. NASICON, / LISICON. SISICON
1 I
j Poro~ts glass I suppons for catalysts, filled with plastics 1
1 Encase mchoactive waste
!Ommllsormoars 1 Mixed i n o r g a n i c ~ c netwodcs with
- ; Organic and i n o m network modihx
Ln the plnrmt investigation, the sol-gel p r o m is used to prepan the lithium tmcdkatt 1&0 - &OJ - sib] (LBS) & lithium phosphobom3ikabc - has - m - =a1 mI sys-.
The SIC glassy compounds can be characterized by different techniques
like XRD, FT'IR, Raman Spcctmsmpy, NMR, TCA, DSC, SEM, TEM, EXAFS,
IIKEM, XPS, UVPS, Auger electron Spectroscopy, &cfmn energy loss
Spectmeapy, (EELS) and ESR 11-4,251. In the present investigation, some of the
tcchmques used to c h a r a c ~ h the solid electrolytes prepared by both melt
quench and sol-@ pproasses briefly discussed are X-ray Difhaion (XRD),
Fig 2.5 shows the experimental setup used for the conductivity measurements in
the pnatnt invesugation. The sample pellet, unda the investigation, is
sandwiched between the two polished surface silver disc electrodes and the two
discs m connected to the measuring instrument (LC2 meter) through tellon
coated purr silver thm wires to minimize the contact resistance. The chrome1
alumel (CY-Al) thamcauple were used to measure the temperature. The whole
arrangement is kept inside an wacuable th~ck glass tube sealed with aluminum
rap. The real (Z) and maginary (2") parts of impdance were measured, at a
pnssum rangr f i ~ m 10 to 1 0 7 tom, uslng lieithely 3330 LCZ meter, in the
frequency range of 40 Hz to 100 kHz as a function of temperature ranges born
293 to 723K.
The real (2') and imaginary (2") parts of the impedance were adyzed
using the Boukamp equivalent circuit software to obtain the equivalent circuit
and the bulk resistance (Rb) of the sample 13 1-33]. The conductivity is calculated
using the equation 2.8
where, W h the bulk &tana, r is the radius and t is the thickness of the
-plcpdkt.
k 2.5. Schanatic -- of the aonductivity setup, Dl & D2 - silver discs, LI th k d h r leecfe, TI & T z - t h m u p l s , C- Sample, S-Spring, O-ring, C-vacuum stop a&, R-Suppomng rod, J-Outer jacket and F-fumacr
The real c' and imaginary c" pats of the complex dichtric constants were
obtained using the complex impedance data (Z' & Z') fmm the equation 2.9 &
2.10
where d is the thickness, A is the arm of the pellet, o is the angular frequency
and ~o is the permittivity of the fiw space.
The nal M' and imaginary M" parts of the complex modulus were obtained using
thc complex impcdancc data (2' & Z") fmm the equation 2.11 86 2.12
The ekctrical modulus data were m d y z d by Moynhm et a1 method using
h W decay function and the d e t d description is pmented in chapter IV.
The tectols that affect the conductivity arc ck tmde material, amtact
-, pfletiaing pnssurc and t a n p t u r c .
Electrode Maasial
~lectlpde chosen generally should bc good conductom and
s u m the && spdes to h easily and atchane: the mobik ium with
34
the electron in the external circuit to m h h i z the polarizition dfects. Different
~ypa, ofelectl?ode materials arc studied, and from that, it is found that graphite in
~uopmpanol colloid paint and platinum paint coating are the best electrodes
!-use it provides a miao contact between electrode and the solid electroiytes.
Contact rcsistana
Contact bawatn the electrolyte and the electrodes must be made proper to
r d u m the contact mistance offend by the interface.
Conductivity incrmses as the pelletising pressure increases and when the
density of the pellet is almost equal to that of the bulk material, the conductivity
%ill nech a saturated value and thLs is taken as the optimum value.
The conductivity of the sample inueases with incrrase of ternperaturr and
the behavior is fitted to the Amhcnius quation.
where, is the pmcxpommtial factor, k is the Boltzmann constant, T is the
absolute tanpaeNre and E. is the activation energy. The prr-exponential fador
Q and magy E. an obtained from the linear fit of the measured
mnductivib with taqxmtu~ to the equauon 2.10.
1. S.Chandra Super Ionic Sofids Principles and Applications', North Halland Publishing Company, (1981)
2. Tetsuichi Kudo, Kazuo Fueki Solid State l d c s : KIYdansha Ltd., Tokyo & VCH publisher, New York, ( 1990)