PREFACE
Solid State lorries, a new btanch of Material Science, has recently become very popular and challenging duf' to its tremendous scope in solid state electrochemical device
techuology. This branch of sci<'IH'e mainly d<·;tls with physics, dl<'lllist.ry and kdonologica.l aspects of fast ion conduction in solids. The research activit.y in this area
ba.sically concentrates on :
• to develop new solid state ionic materia.ls which should appropriately support
1.1"' new<'!' tcclnoolof!,ica.l inventions; and
• to understand the basic mechanism of fast ion conduction.
The solids exhibiting fast. ion conduction are termed as, Superionic Solids or
Solid Electrolytes or Fast Ion Conductors. Typically, the ionic conductivity is ~ 10- 1
-10- 4 S.cm- 1 at room temperature, which is comparable to the conductivity of liquid/aqueous electrolytes. Thus, the electrochemical devices based on these solids can
overcome several major limitations of liquid electrolyte based devices. The miniaturization of these all solid state devices is also possible. Some important potential
electrochemical devices are : solid state ba.t.teries, fuel cells, sensors, electrochromic
disp 1ay devices (ECD's), biomedical devices etc.
Aller the discovery of fast Ag+ and Na+ ion conductions in Mi\g4 l 5 and /3- alumina respectively in 1967, a large varicf.y of supcrioroic materials with various cation
and anion couducf.ing species such a., Ag+, \u+, Li+, Na+, K+, H+, F-, o- 2 et.c.
loavr been disco\'C·rcd in I loP last. lion·<· d .. cades. On l.loc basis of t.hrir microsl.ructurr and physical proprrtirs, these solids aoe presently classified int.o broad categories
likr fram<'work rryst allinr/pol.wryst allinr solids. compositr or disprrsed elect.rolyt.cs.
polynwr rlrct roJ.,·t.rs. glassy/ amorphous rl<'cl rol,·trs rt c. Thr prrsrnt i m·<'st.igation
roncrnlo;olr•s on :\p;+ ion <onductinp; solids in p;lasS\·(amorphous phase. Prior to Ill<'
work r<'port<'d in this th<'sis. majorit)· of :\g+ ion mnduding glasses, <'xhibit.ing high
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PREFACE
VIII
Ag+ iou condudion at room t.emperat.ur<', were Agl-ba.sed solids. Agl is well known for
its cha.ractcrist.icsupcrionic o- pha.se af1.<•r ~ 147°C. Using Agl as a common host salt.,
superionic gla.sses were preparetl hy rapidly quenching t.he melt. of the salt wit.h the
glass modifier ( Ag 2 0) and various network formers like B 2 0 3 , Cr0 3 etc. In a. recent investigation, we prepared a new compound : a quenched/o.nnea.led [0. 75Agl:0.25AgCl}
mixed sysiem.jsolid solution, exhibiting several transport parameters superior to Agl,
including identical transport characteristics viz. f3 --?a- like transition at a relatively low temperature. Thus, it was expected that Ag+ ion conducting glasses with
higher conductivity would result when this alternate host compound is used in place
of conventional salt Agi. Three new fast Ag+ ion conducting systems were prepared
by melt-quenching this a.lkrnate host with a glass modifier (GM) Ag 2 0 and different
glass formers (GF) vi%. B 2 0:1, MoO,~, Cr0:1 in dif!'cr<'nl. mol. wt .. (%) proport.ion.
The cha.ra.ctcriza.tion of the t.r~.nsport. properties viz. the elect.rical conduct.ivit.y (a),
io11ic nJohility (/'-), !Tiohik ion corwcrd,nltion (n), ionic 1.ransfcrc·rwP nurnh('t' (t.irnJ~
ionic drift. velocit.y ('nd) et.c. were done hy <'lllployillg various experimcut.al techniques.
Structural and thermal characterization studies were carried out using XH.D and DTA
techniques. The optimum conducting compositions, obtained in these studies, were
used as electrolytes for the fabrication of solid state ba.t.teries. The battery discharge
characteristics were studied under various load conditions. The work reported in the
present thesis has been divided into seven chapters.
Chapter 1 gives an extensive overview of the field of solid state ionics incorporating the earlier developments and present classification of superionic materials.
General theoretical aspects explaining the fast ion conduction in these solids are covered. However, the models/theories proposed for the fast ion conducting glasses are
revi('wed in a greater detail because these systems concerned the work of the present
thesis. A brief mention of various potential solid state electrochemical devices is given
in the last of the chapter alongwith the scope of the present thesis.
Chapter 2 describes various methods of sample preparation and the details of
st.ruct.mal, thermal & t.ransport. property charact.erizat.ion techniques. The systems
studied in t.he present. invest igaf.ion are :
( i\ ) X [0. /.'it\!!,1:0.2!; A!!,( 'II:( 1- X) [ A!!,,O: II,O,,j
(B) D. 7[0. 7'JAgl :0.2.'i:\gC'IJ :o.:l[.dg,O:( 1-.v) B20:,j
(:\) x[O. i'!i:\gi:0.2!i:\gCij:( 1-x }[:\g 2 0:Cr0 1]
PREFACE
IX
System (B) was prepared to study the cf[ect of various GF/GM ratios on the conductivity of the optimum concluding composition of System (A). In order to prove that
the new host is a. better alternate host t.ha.n the couvcutiona.l salt, Agl, systems similar
to (A) & (C) were prepared in the identical manner using the conventional salt Agi
and room temperature conductivity values were compared. Impedence Spectroscopy
(IS), Transient Ionic Current (TIC) and Wagner's d.c. polarization techniques, used
for the measurement of various ionic transport parameters viz. 'a', '!1', 'n', 't;on', 'v/,
etc. are discussed in detail in this chapter. At the end of the chapter, the configuration of solid state battery and the method used for studying the discharge behaviour
are given.
The results of various experiment.aJ mca.surcment.s such as viz. compositional &
temperature dependence of conductivity, X-ra.y dil!'raction, ionic mobility, mobile ion
concentration, t.rans((,rem:e numlwr a.nd ionic drift velocity de., carried out on System
(A), <1.1"<' dis< uss<·d ill CIH>ptn :1. TIH' COlllfHJSit.ioll : 0.7[1l.71iAgl:!l.2fJAgCIJ:O.:I[Ag10:
B20 3 ] exhibited the optimum conductivity at. room temperature and the XRD studies
revealed that it is in the complete glassy/amorphous phase. The observed transport
behaviour is interprctated on the basis of existing models.
As mentioned above, System (B) was prepared just to examine the effect of
variation of GF jGM ratio on the conductivity of the optimum glass conducting composition of System (A). Tlw composition: 0.7[0.75Agl:0.25AgC1]:0.3[0.833Ag 2 0:0.167
Bz0 3 ] exhibited further improvement in the room temperature conductivity, however,
the phase turned predominantly into crystalline/ polycrystalline phase with partial
presence of amorphism. Results of different experimental studies similar to System
(A) are discussed in Chapter 4 giving appropriate explanations.
In Chapter 5 , we have' presented thr results of our experimental studies on
Sysl.e111 (C). The glass flH 111<'1' ( 1! 2 0:.) of the Sysl.crn ( !\) has IH'<'I1 n·placed by another
glass formrr (CrO,.). The composition: 0.75[0.75Agi:0.25AgCI]:0.2.5[Ag 2 0:Cr0 3 ] exhihit,·d i.IJ<• opl.innnn co11dndivil.y ;l1worn i.<'JIIj><'l'atttn· and the slructttral dmracl.erization studies revealed the presence of mixed phases (crystalline/polycrystalline plus
arn01phous) in the system.
In Chapi.Pr fi, thP fH'ITonnauc<' of th<· solid state hat.f<·ries, fabricated using
the optimnm conducting compositions of S.l'st.<•ms (:\).(B) and (C) as electrolytes.
are presented. :\g-metal was used as a anode. whil<' (C+I 2) in ratio (1:1) wa$ used
as a cath()(k. The batfrorirs II'<'I<' rlischargt·d at room temprrature under differrnt
load conditions. Fmilwr. ionic transfrrrnce rnunlwrs for tiH'se syslf'ms were also
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PREFACE
tletnmincd using !.he elecl.rocll<'rllica.l cell pol.cnl.ial rrrel.lrou and cornpared with t.he
values obtained earlier using Wagner's d.c. polarization method.
Fi11ally, Chapter 7 summarizes the total workdone of the present thesis once
agam.
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