fndian Journal of Pure & Applied Physics Vol. 37. April 1999. pp. 294-301

dc Polarisation: An experimental tool in the study of ionic conductors

Rakesh Chandra Agrawal

So lid State lonics Research Laboratory. School of Studies in Physics, Pt Ravishankar Shukla University, Raipur 492 0 I Q

Received 3 February 1999

dc Polarization technique has long been in use as an important tool to look macroscopically at the transporting ions and to understand ion transport mechanism in number of sol id electrolyte systems. Wagner 's dc polarization method is one of the most widely used technique to evaluate the extent of ionic/electronic contribution to the total conductivity in the ionic/mixed conductors. Variety of new experiments based on dc polarization techniques have.been developed in the last - 2 decades. The present article deals with some simple but powerfu l dc polarization technique as well as a novel polarization/self- depolar ization method. recently developed in the present laboratory. to study persistent-polari zation/memory- type/electret-type phenomenon in some Ag + ion conducting systems.

1 Introduction Fast ion conducting so lids, also termed as ' superionic

so lids' or 'solid electrolytes ', are a special c lass of so lid

state ionic materials w hich exh ibit exceptionally high

ionic conductivity (-10-1 _ 10-4 S.cm-I) comparable to

the conductivity of liquid/aqueous electrolytes. These

so lids show great promises in recent times to develop

re li able and effi cient so lid state e lectrochemical devices

such as batteries, fuel ce ll s, sensors, memory and elec­

trochromic display devices, supercapacitors etcl.9

. The

mechani sm o f high ionic conduction in these so lids is

governed by number of ioni c transport parameters viz .

ionic conductivity (a), mob il ity (~), mobile ion concen­

tration (n), ionic transference number (lion) , ionic drift

ve loc ity (Vd) as we ll as the energ ies invo lved in varioLis

thermally activated processes. Hence, to understand fast

ion conduction vis-a-vis to characterize the ion transport

phenomenon in these solids, it is imperative to have

quantitative information of these bas ic transport pa­

rameters. A wide variety of experimental techniques are

employed to determine these parameters3

. Some of the

widely used techniques are:

• Impedance spectroscopy (IS) for a - m eas ure-10

ments ;

• T rans ient ionic current (TIC) techn ique for ~ - meas-II 12 I d .. f urements . . Subseq uent y, etermlnat lon 0 n

from a and ~ data using the well- known general

equation for conductivity : aCT) = neT) q~!(T) where

a , ~ and n are temperature dependent parameters;

• Wagner' s method for li on - measurement l3. Sub­

sequently, Vd can be determined from the data ob­

tained in the above experiments . IS is basically an ac technique whi le TIC and Wag­

ner's methods are essentially dc polarization methods.

Since the pure ionic/superionic solids obey the Ohm's

law pretty well i.e. the instant initial tota l current (fT)

varies directly as a function of the dc potential (II) applied across the specimen when V is kept be low the

decompos ition potentia l of the sample material. Hence,

de po larization method can be considered to be one of

the appro priate technique to determine some bas ic ionic

parameters which in turn would he lp us to explain the

ion transport behaviour in these so lids . As the present

paper is aimed at to deal with dc polarizat ion studies, we would, therefore, confine ourselves to this technique

only. In the subsequent section various experimental

methods, based on dc polarization, have been dealt with

including Wagner 's and TIC techniques along with the

results obtained earlier from these studies on some Ag +

ion conducting systems. A novel polarization/self-depo­

larization technique l4, recently developed in oLir labora­

tory to study persistent polarization/ e lectret-type

phenomenon in some Ag+ ion conducting sol ids, has

also been incorporated in this sect ion. Apal1 from TIC

technique, other method suggested for the estimat ion of

•

AGRA W AL: de POLARISATION 295

nand)l are: homovalent doping method for glasses I5- ' 7,

field assisted diffusion method '8, '9, Hall effect20.21 (for

details, please refer to the original papers).

2 dc Polarization Technique The use of dc potential as an experimental tool can be

thought to have initiated just after f araday proposed his laws of electrolysis. It was employed mainly for the purpose of electrolysis of electrolyte solutions. How­ever, in the present times, many modem industries ex­tensively employ dc potential for electroplating various kinds of metals .

2.1 Review of earlier experimental results Ionic transference number and drift velocity meas­

urements - The transference number g ives a quantita­tive information of the extent of ionic and electronic (electrons and holes) contribution to the total conduc­tivity (crT)' Since, crT = crion + cre.h, the ionicl electronic transference number can be defined as :

tion = crion I crT = l ion I Ir le.h = cre.h IcrT = le.h I h

where crion Icre.h and l ion Ile.h are the conductiv ity and current contributions due to ions/(e lectrons/ho les) re­spective ly. The tota l current is expressed by the usua l equation: Ir = n qVd A , where q is the charge on the ion and A is the area of cross-section. The ion ic transference number can be determined accurate ly either by Tubandt method or by Wagner ' s method. The ionic drift ve loc ity can be evaluated usi ng Ir and n data obta ined from Wagner 's ' current versus time ' plot and T IC technique respective ly.

Tubandt 's melhod - Probably, T ubandt22 for the first time used dc po larization method as a too l to determine io ni c tra nsfe re nce numb e r (tion) in io ni c so lid s . Tubandt ' s method was princ ipa lly based on Faraday ' s laws of e lectro lys is. When a dc potentia l appears across an ionic so lid sandw iched between two e lectrodes, the mobile positive and negati ve ions move towards the electrodes of oppos ite polariti es . If the e lectrodes are such that the ions would d issolve into them, then the mass of the electrodes w ill increase. The measurements of change in mass of the e lectrodes as we ll as tota l amount of charge passed through the e lectro lyte of a coulometer, connected in the externa l c ircuit, he lp us to determine ionic transference number. An exce ll ent de­scription of the Tubandt ' s technique appeared in the literature3

.23

. Improving the des ign of hi s original ce ll , Tubandt carried out tion-measuremellts on a-Agl . A dc potential was applied across three cylindrical pellets of

Blocking electro Non-block In9 '- eltetrod.

lottlry

r-----=( +..::):tI (_ )

som~le R

Key

(0)

--- ---- ------- -- --- ----1-1-~ \ ~on= "':T'" (b)

~ IT lion ... :::J U

Tlml'

Fig. I - (a) Schematic experimental circuit fo r lion - measure­ment by Wagner' s method; (b) typi cal current versus time plot

AgI packed together in between Ag and Pt-metal elec­

trodes. Ag + ions, the only mobile ions in Agl, move fro m

Ag-anode towards Pt- cathode . He found that the weight

lost by the Ag-anode was equiva lent to the weight ga ined by Pt-e lectrode and Agl cy linder attached to it.

Thi s was in tum equivalent to the tota l amount of charge

passed through the coulometer. Hence, IAg+ = '1 which was indicative of the fact that AgT ions are the sole

charge carriers in a-Agl. Takahashi el al.24 modified the

T ubandt ' s geometry a littl e and carried out tion - meas­urements in num ber of fast Ag + ion conducting systems.

Wagner 's method - This is a most convenient and

w idely used method suggested by Wagner and Wagner in 1957' 3 to measure ionic/electronic transference num­

ber in number of solid electrolyte systems. The tech­

nique g ives very re liable results particularly in case of Ag + ion conducting so lids. Hence, the present d iscuss ion is limited to study Ag+ ion conducting systems on ly. However, it should be mentioned here that thi s tech­nique is extensive ly employed, in general , to study other

so lid e lectro lyte systems a lso . The experimental ar­rangement for the determ ination of tion in a Ag + ion

conducting system is schematically shown in Fi g. I (a).

A cy lindrical pe llet of the sample is sandw iched between blocki ng (graph ite) and )1 on- blocki ng (si lver) elec­

trodes . A constant dc potential (V - 0.5 V) is appl ied

across the samp le w ith the po lari ty shown and the cur­

rent in the c ircuit is monitored as a function oftime with

the help of an x-y-t recorder. A typical ' current versus

296 INDIAN J PURE & APPL PHYS, VOL 37, APRIL 1999

6

It

2

0.6

0(- Rl9ion

20 -lr{2I00C)

.... ITCC)9·C) IT - TOTAL CURRENT 10

1,.<12S-c)

ITC60·C) 0

IT(27"C)

Ir (152·C) Ir(187·C)

2 4 6 (h)

8 10

Fig. 2 - Current versus time plot for Agl

time ' plot is shown in Fig. I (b). Silver ion conducting systems are generally pure ionic systems with Ag+ ions

as sole charge carriers. For such a system the total

current h approaches zero as a result of complete deso­

Jution of Ag + ions in Ag-anode. Since, h ~ lion ; li on = I. However, if the so lid is a mixed Ag+ ionic/electronic

system, the total current h levels off at some non-zero value, as shown. The final residual current (Ie.h) is due

to the moving electrons/holes in the system . Hence, lion

and te.h can be known separately with the help of the

ratios: lion / hand le.l,lh respectively. The current versus time plot of Wagner's dc polari­

zation method can also be employed to estimate the drift

ve locity (Vd) of mobile ions in a pure ionic solid, as

discussed above. This novel approach was used for the first time by the present group to determine Vd in number of Ag+ ion conducting systems25 viz . AgJ 26.27 ; a

quenched [0.7SAgl:0 .2SAgCI] mixed-system/solid- so-

I . 2829 · . d I b utlOn ' Il1vestlgate at our a oratory as an alternate

host in place of AgJ; glass systems: 0.7 [0.75AgI:0.25AgCI]: 0.3[Ag20 :B20 3] and 0 . 75 rO.75AgJ 0.25AgCI]: 0.25[Ag20:Cr03]30J I and com­

posite systems: 0 .7[0 .75 Ag1:0.25AgC I] :0 .3 A b03,

O.8[0 .75Agl: 0.25AgCI]: 0 .2Sn02 and 0 .9 [0.75Agl:0 .25AgCI]: 0 . 1 Si02 32-34. A representative

temperature dependent current versus time plots for (3 and a phases of AgJ (Region-I and Region-II respec­tively) is shown in Fig. 2 . The temperature dependence

of current versus time plots for all other systems were

-1 ~----.-.---------------~ I .t--- Transition renion « -phase ...

-2

2

~-i- Il -ptBse

I : , - --r-- --I-, I , " I I' I

~'

2.5 3

1oo0lT [K')

3.5

Fig. 3 - Log Vd versus l i T Arrheniu s plot for Ag l

identical and exhibited following significant features in

common: I. The initial current (h) approached to zero with time

at all temperatures of our measurements . This was in­

dicative of the fact that all the systems remain purely

ionic with Ag + ions as sole charge carriers and hence,

l ion ~ I in the entire range of temperature. 2. The polarizing time (i.e. time in which h ~ 0)

increased as the sample temperature increased . This is

expected, as at higher temperatures the mobile ions are

thermally more agitated, hence, wo uld require longer

time to get polarized at a fixed va lue of applied dc

potential as compared to the time required at lower

temperatures . 3 . The magnitude of initial total current (h,) also

increased with increasing temperatures . The increase in I h I may either due to the increase in

nor Vd. If n can be measured independently, Vd can be

eva luated at various temperatures with the help of h -data obtai ned from the above stud ies ( in fact, n has been

determ ined independently with the hel p of (J and /1 data,

as discussed below). A representative log Vd versus I /T plot for Agl is shown in Fig. 3 . Sim i lar plots were drawn

for other systems and the energy (Ed), involved in the

thermally activated process, was computed from the s lope of the straight I ine for all the systems2 5 -3 ~ . I t has

been verified that Ohm ' s law obeyed we ll during these

measurements. Since, Vd is directly proportional to /1 at

a fixed value of applied dc fie ld E (i.e. Vd = /1E) . hence,

log Vd versus liT and log ~l versus I /T variations must

be analogous and the energies Ed and E111 involved in

these two thermally activated processes respecti vely

wou ld be identical. The validity of Vd measurements on

all the above systems were cross-checked by direct

determination o f ~l using TIC technique, as discu ssed below.

AGRA W AL: de POLARISATION 297

Ionic mobility and mobile ion concentration meas­urements - Transient Ionic Current (TIC) technique: TIC technique, originally suggested by Watanabe et a/. II

and Chandra et a/. 12, was used for direct detennination

of 'ionic mobility (11). This is also a dc polarization method, like Wagner's method, except for both the electrodes being blocking. The sample is first polarized by applying a constant dc potential across the thickness of sample pellet for sufficient long time to ensure that a state of complete polarization has been attained. At this state, the mobile ions are polarized and remain blocked at the respective bulk/electrode interfaces. The polarity of the applied potential is then reversed, simultaneously, the current in the circuit is monitored with time. The instant the polarity is reversed, the polarized ion clouds start travelling in the bulk towards electrodes of opposite polarity. This results in a flow of current through an external circuit. The moment the ion cloud arrives the other end of the pellet, a peak occurs in the current versus time plot, and then the current drops sharply. Fig. 4 shows TIC plot for a typical system in which only one type of ionic species are mobile. The inset shows the basic experimental arrangement. I f more than one ion ic species are mobile in the system, number of peaks would appear in TIGplot when suitable blocking electrodes are used. Each individual peak would correspond to one type ofmobile ionic species. The position of the peak on the time axis directly measures the time offlight"t of the mobile ion species to cross the thickness d of the sample pellet. Hence, the ionic mobility 11 can be determined with the help of equation : 11 = if / V "t, where V is the applied fixed dc potential. Using the Il-data obtained above and a-values from conductivity measurements, mobile ion concentration n can be evaluated conven­iently for the systems with one type of mobile ionic species. The temperature dependent measurements of 11 and n can also be carried out by placing the specimen in a furnace. The energies (Em and Ef) involved in the thermally activated processes can be computed from the slopes oflog 11 versus I/Tand log n versus I /T Arrhenius plots respectively. These measurements were carried out on the above mentioned Ag+ ion conducting system s25

-

34 . On the basis of the experimental resu Its, the phenome­non contro ll ing the basic ion transport mechanism in these sol id electrolyte systems can be 'easi Iy understood. Detailed discussion on the mechanism of ion transport in these Ag t- ion conducting solids appeared elsewhere in the literature 26.34 .

-c ~

.a ... ~ ... c .. ... ... :)

U

River, kty

2 Furno!' ,

Sample

lOO.n.

I I I \

\ , , <

0 0 10 20 30 60 90 120 150

Tlmt' (,)

Fig. 4 - Typical TIC plot for !-I-measurement. Inset: the basic experimental circuit

Miscellaneous dc polarization experiments - Vari­ous miscellaneous experiments, based on dc polariza­tion, have recently been suggested by a number of workers. Yoo and coworkers35 designed an experiment based on the polarization in an ion-blocking electrode condition and determined ionic-charge-of-transport (a*) and chemical diffusivity (D) in mixed conductors. Preis and Sitte36 have recently given an excellent theo­retical treatment for the polarization process occurring in mixed ionic/electronic conductors. Assuming the po­larization as a chemical diffusion-induced phenomenon , they developed experimental model based on Weppner and Huggins37 asymmetric electrochemical cell con­figuration and determined chemical diffusion coeffi­cient in mixed conductors with comparable ionic and electronic conductivities by means of galvanostatic po­larization experiments . Mizusaki38 has recently sug­gested a novel and improved experimental technique to study the bulk and interfacial properties of sol id electro­lyte systems. His technique was based on Hebb- Wag­ner ' s ion blocking method39 by dc polarization field using the cell configuration : (- )Agi AgX (X = C I, Br, I) I C or Pt(+). It was shown that the complete ion- blocking can be realized when the chemical equilibrium is at­tained not only at the Agl AgX interface but at AgXIC interface al so.

2.2 Polarization/self-depolarization and persistent­polarization/electret··type effects in some Ag + ion conductors

Another novel idea, based on dc polari zat ion method, has recently been developed in our Laboratory to study po larization/self-depolarizat ion phenomenon in some Ag~ ion conducting systems. The polarization procedure

298 INDIAN J PURE & APPL PHYS, VOL 37, APRIL 1999

was exactly similar to TIC technique discussed above. The polarization/accumulation of mobile Ag + ions at negative polarity end of the bulk specimen results in a potential difference across the sample pellet which can be measured experimentally 'on the removal of the ex­ternal dc potential. The magnitude of the potential dif­ference, obtained at the instant the external dc potential is removed, corresponds to a peak value and can be referred to as instant peak potential (Vp). Vp decays rapidly due to redistribution/self-diffusion (chemical diffusion) of accumulated ions throughoutthe bulk. This process has been termed as a self-depolarization phe­nomenon. In order to explore the time exactly required by the specimen to attain the state of complete polariza­tion, the external polarizing dc potential was applied for different durations and Vp-values were measured. Fig. 5 shows instant peak potential Vp-values measured at room temperature on pellets of different thicknesses of AgI, [0.75AgJ: 0.25AgCI] and a superionic borate glass system : 0.7[0.75AgJ:0.25AgCI]: 0.3 [Ag20:B20 3]. The abscissa corresponds to the time (I) for which the sam­ples were initially polarized. One can note from tlie figure that Vp increases initially as the polarizing time increases then attains a saturation value afterwards. This corresponds to the state of complete polarization and gives an information about the minimum time needed for the above Ag + ion conducting systems to attain the state of complete polarization . One can also note that the magnitude of Vp increases with the thickness of the samples . This may be due to the reason that in thicker specimen, number of mobile Ag+ ions are expected to be more which in turn get polarized and give rise to larger Vp-va lues as compared to that for the thinner sample. This is a qualitative and not a quantitative statement. The experimental results in Fig. 5 clearly indicate the fact that the magn itude of Vp at the state of complete polarization gives a qualitative information regarding the number of mobile Ag~ ions available in the system at a particular temperature. We carried out temperature dependent Vp- measurements . The assertion drawn from the above study regarding Vp-values giving infonnation about the mobile ion concentration n is further supported when we compared Vp versus tem­perature plots with the plots of temperature variation of n for these systems obtained earlier in the independent studies26.28.10. Fig. 6 shows log Vp versus I /T plot for: Agi (thickness -0.205 cmt, [0.75Agl : O.25AgCI] (t hi c k n e s s -0 .2 c m) and sup e rio n i c g I ass : 0.7[0. 75AgI :0.25AgCI] :0.3 [Ag20:B20 1] (t hi c k n e s s

&Xl ... - _ . .. - . _ ....... - --.. --.---.--.--...... - -

Thickness I ~O.2C6cm -O.2fficm O.~ ~

> =--=-=. ] £.:m =

~ ::;;,

"' Co > /

I

I

200 (i-ti !: = !! ~ Temperature -2'fC

(a) i

100 L

> £..m Co >

_._---­- -- ---------.--_.---- ------ - 1!

Thickness 1 ~ 0.135 cm - 0.167 cm 0.2 em I i i

no ... wi

.~ i r== .J ~ .. VSOi( "If

~. ~ Ig.like ohase at -2f:ftc l 1 .....: 7 . ~

=/~= ~I ~ .'!/ 1iiii _ .. ~

i/ ~ ohase at -2'fC I 1 4 ~

(b)

_ _ .'_ " _ __ _ . .. . . .-. _~-.. __ .--__ ~. ____ ~.~ ..... r ... .,.......",...~

ThiCk'ness l ~ 0.155cm =0.215cml~

". :m ~~~-----------------------~

~ ~ I Co

>200 Temperature 2'fC

Fig. 5 - I 'p versus polarizing lime plols for : (a) Ag J: (b) [0.75AgJ:0.2SAgCI) : (e) 0.7[0 .75AgJ:0.25AgCI) 0.31Ag20B201J

(c)

-0.155 cm). Log n versus l i T Arrheni us plots for these

systems are reproduced in Fig. 6 for direct comparison.

One can obviously visua lize that Vp and n vary almost

analogously with temperature for all the systems. We

note an abrupt increase in Vp-values for AgI and the new

host [0.75AgI :0.25AgCI] , after f3 --+ a transition tem­

perature. The abrupt increase in Vp after the phase tran­

sition further justifies our other assertion we made

earlier26.28, regarding the superionic conduction of a ­

AgI or a -like phase of new host, as due to an abrupt

increase in the mobile ion concentration (n).

AGRA W AL: de POLARISATION 299

3 '-\l-~--:-' -.'---Tra-ns- it-i-o-n-reg-io-n -(-a)----,j :

>' 2.8 ~.... 1 13 iNse ' .i .5. _........... ~ 18:;,

~2.6 16]'

! 2.4 ~ 14.Jo L •

2.9 ... ----",.--,:----- ' ~ Transition region

13 -like phase

, . 3 .------ - ----- - ---, 24

~ 2.8 r ~ 2.6

!r ..J 2.4

2.2 L.....__'_~~_'__'~~~ ........... ~__'_~ 12

2,0 2.5 3.0 3.5 1000lT [K"'l

Fig. 6 - Log Vp versus I IT and log n versus I IT plots for : (a) AgI; (b) [O.75AgI:O.25AgCI];(e) O.7[O.7SAgI :O.2SAgCI] : O.3[Ag20:B203]

In addition to the above novel information, a phe­nomenon of persistent-polarization/electret-type effects were also observed in AgI I4 and the new host [0.75AgI:0.25AgCI] during self-depolarization cycle. This is probably another remarkable feature exhibited by mobile Ag + ions of the system . These effects corre­spond to electret-type behaviour commonly observed in several dielectric materials such as polymers, divalent impurity doped ionic salts viz. KCI, Kl, AgCI40 etc. Kumar and Chandra 41 have reported electret-type effects

in solid electrolyte mixture : RbAg4I5+ KEr, which they referred to as ionic polarates. Electret-type effect, in fact, refers to a phenomenon in which the polarization state persists for a long time after the dc polarizing potential across the sample is removed. For details,

~ b d h .. I I' 42 43 relerences may e rna e to t e onglOa Iterature . . The electret-type effects become more predominant or the polarizati~n states persist for longer duration in

'thermally stimulated polarized ' samples i.e. samples polarized at higher temperature. We studied this effect in thermally stimulate polarized Agl (thickness -0.205

.4aJ c i At instant I 300

2ID (a)

1~ I_ CooUng cycle i- ~ 50 . .::. Healing cycle I ~

=r··· -~ • • - •••.•. . • ,. - .... -" .• -, ~ .~ - ... ~-.- - I

After 8 h I I

:1 L.. ~~~"----,,---,-_.~~.~_;~,~~~~a--,)

400 r------.-... -.-... -.'-.... ~---.-. P=''A=fte=r'''''iu=h''''''1

:;,:m !.200 (b) i Q. > 100

o ~~~~~~~~~~~~~~~

3lJ

200

100

o ~~~~~~~~~~~~~~~

2 2.5 3 3.5 1000/T (1<"1)

Fig. 7 - Vp versus l iT plots showing persistent-polarizalion in:

(a) Ag\; (b & c) [O.7S AgI:O.2SAgC I]

300 INDIAN J PURE & APPL PHYS, VOL 37, APRIL 1999

cm) and [O.75Agl:0.25AgCI] (thickness -0.2 cm). The samples were poll;lrized by an external dc potential (-0.5 V) for 10 min at 200°C (i.e. well above (3 ~ a transition temperatures, -147°C for Agl and -135°C for [O.75Agl :0.25AgCI]), then the external dc potential was re­moved. The potential difference developed across the sample was measured during different thermal heating/ cooling cycles in the time span ranging from I to many hours. Fig. 7 shows the 'peak potential versus tempera­ture' plots fo r these systems. The upper plot in both Figs 7a & 7b gives the variation of potential immediately after the removal of the field at 200°C and cooling the sample to room temperature (1st cooling cycle), then heating the sample back to 200°C (1 st heating cycle). A hysteresis type behaviour was observed in both the cases. Hysteresis generally corresponds to some kind of energy loss in the systems. The other plots correspond to the variation of potential difference in subsequent heaJingicooling cycles of the same samples which were left open at room temperature for several hours. It can be obviously noted that, although, the magnitude of potential decreased with time, but, the polarization states persisted for very long time . The potential differ­ence measured at higher temperatures may be thought to be due to the existence of temperature gradient be­tween upper and lower electrodes i.e. a typical thermo­emf measurement in the usual thermoelectric power studies on ionic/superionic systems. However;this was overruled after performing the same measurement on an unpola rized Agf sample . This is obvious from the bot­tom-most plot in Fig. 7(a) which shows that the potential difference remains close to zero at all temperatures. The persistence or retention of polarization field substan­tial ly improved in the samples cooled to room tempera­ture from 200°C with polarizaticn field on . This can be obviously seen in Fig. 7(c) showing the similar plots during various heating / cooling cycles for [0.75Agl:0.25AgCI] sample cooled from 200°C to room temperature with polarizing field on and then the field was removed. The polarization state in this sample persisted for more than 350 hrs . In the dielectric electret materials this kind of polarization-state-retention have been reported due to homo-charge formation and de­ca/ 2

,43. The similar reasons may probably be assigned to above ionic systems also . However, an extensive investigation is needed to explain such phenomenon in ionic solid:;. Nevertheless, to give an approximate ex­planation, one can think of a memory-type-effect for mobile Ag + ions of the above systems polarized in the

high conducting phase and make a vague statement as : it seems as if 'the mobile Ag + ions have retained the memory of their polarization state at a particular tem­perature and the memory died out slowly with time '.

3 Conclusion On the basis of various experimental results dis­

cussed, it can be concluded that the dc polarization technique can certainly be employed as an important tool to study ion transport (macroscopic properties) in several ionic/superionic and mixed ionic/electronic sys­tems. What is actually required is ; an ingenious design­ing and development of new experiments. The dc technique is widely used in many Solid State fonics Research Laboratories, including the present Labora­torY" to measure ionic/electronic transference number, ionic mobility and ionic drift velocity etc . Based on this technique, another novel method has recently been de­veloped, to study the polarization/se lf- depolarization phenomenon and persistent-polarization effect in some Ag+ ion conducting solids. The results have been di s­cussed with reference to electret-type effects, com­monly observed in dielectric material s.

Acknowledgment The author gratefully acknowledges the financial

support provided by the MPCOST, Bhopal, through project No . P-86/92 cit. 16/12/94.

References I Fast ion transport in solids. Ed W van Gool. (Nort h Holland.

Amsterdam), 1973.

2 SuperionicconduclOrs , Eds G D Mahan & W L Roth (P lenum Press. New yark). 1976.

3 Chandra S. Sliperionic solids- principles and applications. (North Holland . Amsterdam). 198 1.

4 Superionic solids and solid electrolytes: recent trends. Eds A L Laskar & S Chandra, (Academic Press, NY), 1989.

5 Boyce J B. DeJonghe- L C & Huggins R A. (eds). Solid state ionics - 85 (North Holland. Amsterdam), 1986. Vol. 18 & 19: Hoshino S, Ishigame M, Iwahara H. lwase M, Kudo T. Minami T, Okazaki H. Yamamoto O. Yamamoto T & Yoshimura M, (eds), Solid state ionics - 89 (North Holland, Amsterdam) .

. 1990. Vol. 40 & 41 : Ni cholson P S. Whittingham M S. Farrington G C. Smeltzer W W & Thomas J (eds). Solid state ionics - 91 (North Holland. Amsterdam). 1992. Vol. 53-56: Boukamp B A. Bouwmcestt:r H J M. Burggraaf A J. van der Put P J & Schoon man J. (eel s). Solid stnte ionics - 93 (No rth Holl and . Amsterdam). 1994. Vo l. 70-72: Chowdari B V R. (ed ) Solid state ionics - 95 (No rth Ii oli and. Amsterdam). 1996. Vol. 86-88.

6 Chowdari B V R. Chandra S. Singh S & Sri vastava pc. (cds) Solid state ionics. Ma terials and applications. (World Scien­tific, Singapore), 1992; Chowdari B V R., Yahaya M. Talib 1

AGRA WAL: dc POLARISATION 301

A & Salleh M M, (eds), Solid state ionic materials (World 26 Agrawal R C, Kathal K & Gupta R K, Solid State /onics, 74 Scientific, Singapore), 1994; Chowdari B V R, Dissanayake (1994) 137. M A K L & Careem M A, (eds) Solid state ionics: New 27 Agrawal R C, Kumar R & Pandey R K, in: Solid state ionics: developments (World Scientific, Singapore), 1996. New developments, (eds) Chowdari B V R, Dissanayake M A

7 Bruce P G, (ed) Solid state electrochemistry (Cambridge Univ. K L & Careem M A (World Scientific, Singapore), 1996, p. Press, Cambridge), 1995. 493.

8 Chandra S & Agrawal R C, in: Golden Jubilee Commemora- 28 Agrawal R C, Gupta R K, Kumar R & Kumar A, J Mater Sci, tion Volume (ed), U S Srivastava (Nat Acad of Sci, India), 29 (1994) 3673. 1980, p. 429.

29 Agrawal R C, Kumar R, Gupta R K & Saleem M, J Non-cryst 9 Hagenmuller P & van Gool W (eds). Solid electrolytes, Mate- Solids, 181 (1995) 110.

rial Science Series (Academic Press, NY), 1978. 30 Agrawal R C & Kumar R, J Phys D, 27 (1994) 2431 .

\0 Macdonald J R, (ed), Impedance spectroscopy (John Wiley & Sons, NY), 1987. 31 Agrawai R C & Kumar R, ibid, 29 (1996) 156.

II Watanabe M, Sanui K, Ogata N, Kobayashi T & Ontaki Z, J 32 Agrawal R C & Gupta R K , J Mater Sci, 30 (1995) 3612.

Appl Phys, 57 (1985) 123. 33 Agrawal R C & Gupta R K, ibid, 32 (1997) 3327. 12 Chandra S, Tolpadi S K & Hashmi S A, Solid State /onics , 28-

34 Agrawal R C, Verma Mohan L & Gupt,a R K, J Phys D, 31 30 (1988) 651. (1998) 2854.

13 Wagner J B Jr. & Wagner C, J Chem Phys, 26 (1957) 1597. 35 Lee K C & Yoo H I, Solid State /onics, 86-88 (1996) 757; Yoo

14 Agrawal R C, Gupta R K & Verma Mohan L,/onics, (in press). H I & Martin M, Ceram Trans , 24 (1991) 103 ; Lee K C & Yoo

15 Ingram M 0, Machenzie M A, Muller W & Torge M, Solid H I, J Electrochem Soc, 141 (1994) 2789.

State lonics, 28-30 (1988) 677. 36 Preis W & Sitte W, Solid State /onics, 86-88 (1996) 779; ibid. 16 Miller W & Torge M, ibid, 36 (1989) 20 I . 76 (1995) 5.

17 Jorge M, Thesis. Acad olSci. GDR, 1990. 37 Weppner W & Huggins R A, J Electrochem Soc, 124 (1977)

18 Engel J R & Tomozawa M, JAm Cerem Soc, 58 (1975) 183 . 1569.

19 Kahnt H, Kaps Ch & Offermann J, SolidState /onics, 31 (1988) 38 Mizusaki 1, Solid State /onics , 86-88 (1996) 1335; Mizusaki

215. J, Sakai J, Yamauchi S & Fueki K. ibid, 7 (l982 ) 323 .

20 Ckment V, Ravaine 0, Deportes C & Billat R, ibid, 28-30 39 Wagner C, Z Physik Chem B, 21 (1933) 25. (1988) 1572. 40 Capelletti R & Fieschi R, in: Int symp on electrets and dielec-

21 Denoyelle A, Duclot M J & Souquet J L: Phys Chem Glasses, trics, (Acad Brazil de Ciencias, Rio de Janeiro), 1977, p. 131 ; 31 (I990) 98. in Electrets. charge storage in dielectrics, (ed) M M Perlman

22 Tubandt C, Z Anorg AUg Chem, 1 \0 (1920) 234; ibid, 115 , (Electrochem Soc, Princeton), 1973 , p. I.

\05. 41 Kumar A & Chandra S, in: Solid State lonics , (eds) B V R

23 Lidiard A B, Handbuch der Physik, (ed) S Flugge, (f957) Vol. Chowdary & S Radhakrishnan (World Scientific, Singapore),

50, p. 246. 1988, p. 503 .

24 Takahashi T, Ikeda S & Yamamoto 0 , J Electrochem Soc, 119 42 Gross B, Phys Rev, 57 ( 1940) 57. (1972) 477. 43 Perlman M M, in : Electret and related electrostatic charge

25 Agrawal R C, Kumar R & Gupta R K, Mater Sci & Engg B, storage phenomenon, (eds) L M Baxt & M M Perlman (The 57( 1998) 46. Electrochem Soc, New York), 1966, p. 3.