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

MX - dopant salt w, LiBr, Agl, AgCl, AgEk, Nal, Kl, etc.)

M2Y - network madificr Fa, LbS, A@, AglS, CUO, W , Na30, etc.)

A,&, - network forrnrr ISiOl. Pas . VBs, 803, Si&, &Ss, etc.)

From the equation 2.1, another general expression for thne component gkss

forming oxide systems can be r r p m t c d as

whm MX - dopant (Lil, LiBr, Agl, etc.) MzO - modifier (b0, @0, CUO, W,

N@, etc.) &&On - kamcr (3% W s , V2Os, W3, etc.1.

Oisa brmm an compounds of a cwaknt MhlR, which have tht ability

to linm a @m on rufedent h t cuoling. The direct forming char id oxides m 39

SiCh, &Os, P d a & GeOl and these oxides p m d e the backbone to foxm glass.

The other oxide chemicals like VKh, 0 3 , Mo03, etc do not form glass on their

own but can form the glass on mixing with other direa glass foxmjng ox&s or

with the glass modifim. Some axides wiU form the glass matrix by satisfying the

Zachnmicnk aiteria as follow 1 15)

a. An wrygen atom may be linked not to more than two atoms of A

11. The number of cucygen atoms sumundmg A must be small (probably 3 or 4)

c. The oxygen polyhedra s k comers uith each other, not edges or hem

(I. At least t k comers of each polyhedron must be s h a d to form a 3-D

network, by difkrent plrparacive method to form a continuous polymeric random

network. The glass former has a three dimensional continuous random network

structure corn@ of some basic structural units like planar triangular I303

unlts in M>3 glass and tetragomi Si04 in 901 glass.

The glass moddim are M2O = L O , A&O, CuO, W , N a a 0 , etc. which

ruptum the mtinuous networks formed by the glass former, by interacting

strongly with the brsdgod q e g e n Linked to the two cations of the glass formers

(e.g. Si. B, P, Mo, ctc.). This mults in the formation of non-bridgmg axygens

(NBOs) and M' ion weakly bond to NBOs, such that the gbss matrix is modified,

which is orklent'frorn the spcPoscopic studmi as shown in the equation 2.3.

QJ 2.1 a, b & c rnpmiwly show the two dimensional schunatic representation

of ordend, disarderrd and modi6ed framework of SiOl.

I I I I Li*

- a-0-s- + u--+ - B - O 0 -Si - 2.3 I I I

Li'

I ip,, 2.1. TWO mmdod achematic repemtation of4 0dm.d bl and d mob&d SiOl mat&

Ionic halides an generally known to be dopant salts, eg. LiI, NaI, Agl.

These salts dissolve in the glassy matrix and remain dispersed without any

intrractibn with the glassy matrix and hence, no s b f h r a l changes occur.

Thus, halide salts amtribute to the in- in the number of carrier ion

concentration, which in turn nsult in enhancement of the ionic conductivity.

2.3. PREPARATION -QUEB OF OLAS8

Glassy solid electrolytes are p r e p a d in dilTerent forms such as bulk,

pawders, fiber, thin Kim, etc. through various tcchniqus, depending on their

quirrment in the application of SSI devices. However, in n a n t years, many

unoonmtional tcchntques lor pn.cparing glass avoid the use of the molten state,

w M hed marked importance in synthetic field of glassy materials. The

loUowing arc the different techruques to pnpare amorphous/@assy materials 13,

41 arr Thermal evaporation, Glow dm&arge decomposition, Sputtering, Chemical

vapor deposition, Wectrolytlc deposition, Rcaaion amorphization, Presswe-

induced amorphization, Inadiation, Solid-state difhsion amorphization, Melt

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)

aqueous or colloidal and b) alkwide route.

New precursors; Structure of solution, sol ,

I

f i b * sphuff powders

heating rate

crystalline. nonuystaht cemmics ccramir* (xme% e.&, =-a

€lmxxkd

Sd#ne 2.3. The sol-@ proags for maldng &us famLo 43

Colloid: Colloid is a suepension in which the dispersed phase is so small

(-1 to 1000 nrn) that gravitational forus arc neglgible and inttmdom m

dominated by short-rang forces, such as van d a waals and surface charges

inertia of the dispersed phase is small.

Sol: Sol is a colloidal suspension of non-polymeric solid pamcles in a

liqud.

Gel: Gel is n semisolid that contains a continuous solid skeleton enclosing

a continuous liquid phase. Gel has elasticity due to in-& ngd network

with pons of sub-micron dunensions and polymeric chains whose average length

is gmter than a miaon. A gel is said to form, when one molecule reaches

macrrscupic dimension so that ~t extends lhruughout the solution. Gel point is

the time (degra of reaction) at which the I;~st bond IS formed that complete the

gmr rnokuk &I).

ccAiokM prousa involves the dispersion of c o W i sized wdes in

aqueous solvent medium to form a sol. The formed sol is destabilized on a

conmllcd manner, by allo\Kmg the particles to approach each other to overmmt the stabikhg banier operating in it and this could be achieved by hmbng,

frceang, mantratlng adjusting the pH of the sol, or by ad- electrolyte to

obrain a gcl The solvent fmm the gel can be remared by maintaining at a particuler trmpaatun and then sinttnd to give a aystalline/daw amorphous

solid material. This pnmss is npmentcd schematically in the scheme 2.4. The

sin- process is c a w out in one of the following ways: 4 heat treated at

tanpaeturu~ kbw the glass transition temperature to obtain glass through

b) the gd well above the T, but within the melting paint

w w and the particulate to form a glass 13,61.

I Condensation

cyclization and growth

+ dense silica partide with hyrdaxylated surface

/ further condensation

and agglomeration

Silica gel

Schcmc 2.4. Colloidal proctss

Thc sol-gel process thmugh alkoxide route n q u h the use of an

solvent, normally an alcohol, m order to art as mutual solvent for the alkaxide

precursor chands and the water for h.ydmlysis. The abxide mute considers

the bkwmg steps in the synthesis of sol-gcl derived samples 124,251.

~sunrors, Diesdution & Mixmg, Casting, Gelation, A g q , Drying, Chanical

Stabikatbn, DaWcation

Prccurmrs, Discldutian and Mixing

The penumr chanicals involved in the proc*ls arc metal alkuxids of

wide reagt of elments, SI(OGH&, Ti(WHsb, B(oclHs)s, VO(oc1Hsk

Nb(OCBHde, w ( w etc with various alkoxy groups Ni(o& 4s

Et, R" Bun] etc.. In addition, the metal salt Wct nitrate, chloride or acetate ctc. is

also used with the alkoxides as precursor materials in the synthesis 16,241.

Alkoxides [M(OR),,) tend to rcact with all hydmxy compounds resulting in

the replacement of their alk~xy groups. The presence of-&ctmnegative alkoxy

p u p s malang the metal atoms h~ghly pmne to nucleophilic attack. The reaction

with akohol (HOH] [W - Me, Et, FF, Bun] is as follows

The equation 2.4 follows the SNZ type of m c w n and is susceptible to steric

factors. Although, in general, the facil~t?, of interchange of alkoxy p u p s

dcarascs in the ordcr methyl > ethyl > pmpyl >tertiary butyl, yet even for slow

maion the invrchange can generally be pushed to completion if the alcohol

produad in the nection is continuously IractionaM out. Generally, aknides

with difkrent alkyl p u p s show different t-ractivities with water, it is possible to

adjust the rate of gelation of a given alkoxides by using a merent solvent. The

alkrnddc p m u m are organic soluble and are sensitive to hydrolys~ by water.

The selection of solvent to dissok the alkoxide should be water miscible o m

solvent for the better hydrol?.sls and candensation rmction to occur. The

controlled manna of hydrolysis and condensation can be achieved using the

chelaring organic bgmd (organic acids, glwl , or -tones). The solvent

choscn result in a singlcphese solution leading to the imp& homogeneous gel

formation and h a m , the glassff smaurc. The order pf mechanical mixing, the

liquid akcddt prrcursors to h y d r o m by water an as shown in equation 2.5 at

a pH that prevents the precipitation. The rate of heating during the mixing

pmuwi has a marked c&ct on the hornogneity and the purity of the sample.

The hychbda pmduct, e.g. the h - w e d silica tetrahedra, interacts to condenst

618 shown in squatfonrr 2.6 & 2.7. The reactions an

M(oRll, + M(OR)WI(OH] ---* M2O(OR)%l+ ROH cond-tjon 2.6

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),

1:ouricr Translorms Inlrared spectrtrsmpy (FRR), Differential Scanning

(21lorinieuy (DSC) and conductivity by impedance spectroscopy (IS).

X-ray dibction is used to iden* and characterize solids posstssing the

long range and short range order respectively in the uystaliine and amorphous

materiali, 127, 281. In the present investigation, X-ray diElraction studies wen

canied out using RI,@u make miniflex dflractometer with Cu-Ka radiation of

wavelength i, - 1.54 18 AO. 28 values between 3-700, scan rate of 29 per minute

and 500 cps. The X-ray diiraction spectra were recorded, for the h e powdered

sarnpks prrsscd tlghtiy to form a plane surface in a sample holder window and

load on the platform. The XRD spectra recorded for the LBS & LPBS samples

heat treated at di&rmt tanperaturrs to mon~tor the gel to glass form.

Fourier w o r m in- spectroscopy is anploycd to identify the nature

of the badfne koveen the various groups and the mtaJ ions present in the

clusta I$ the 1291. Dqadmg on the envirmunent ammd the

functional gratp, a ahUt fn the shacfiing and bcndh *- is e p d l ~

OW. F m & rNdt fn the bend position, the tumdmg en-t cauld kt

assigned. In the present imetigation, the FIIR specha wen recorded hr the gel

to glans sarnph using Shimdm FllR-8300/8700 spamphotom&r, 4cm-I

resolution, auto gain, 40 nscan, in the frequency range 4000-400 an-'. The

measurements were made using almost t r a n s v t tCBr pellet containing fint

powdend sampks at mom temperature. The FTTR of the sample

recorded showed the progrss of the dried gel to glass and formation of their

bond Linkages at dflitent temperatures.

Diffemttal scanning calorimetry is very efficient technique to determine

the phase transition that omurs in the sample (endothumic or exothemic

reaaion) accornpanted with the change in temperature (30j. A glass is prepad

as a mut t of a phase transformation in which the nucleation and gmwth of

uystals have been suppressed at a m temperature intend near the 'glass uansition' tanpuature p,). In the present investigation, the samples were

s u m to thumal andysis using Mettler Toledo Star System, Module: DSC

82le/XX)/575/4 14183 /5278. The fine powdered sample of about 7.5mg is

plaad in aluminum pan with lid and pressed to form a micropellet, were used for

detumrning the T, at a heating rate of 2 i i m i n . 1 to 5 Kminl imm 323K to 823K

under nitrugen atmosphere.

The transport studks art made on the prcsscd pckts of the h e ground

mpks. In the present study, the process of pellet pqmation is as b h : the

samples w a t gnwad into fine powders by ad- small amount of isoppand.

The wnpk is albwed to dry for some m e in the oven to m w the added

binding &rent n# m p k s an comprrsscd using the KBr press of Spectralab

mkca at a pamcular p m w . The dimensions. of the pellets an l O m m

dtpmeza about 2 4 mrn thickness. The conducting ckCtmde m a w 112

an of graphite colloidal suspension in isopropanol, coated over the p e h on

either Ilat su-. The conductivity measurements werc made on the pellets of

the hm of

Graphite electrude / (LBSI, (LPBS), (LVP) glass ekmlyte /'h.aphite electrode.

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)

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