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The effect of thermal history on the ionic conductivity of Pb(II)-β″-alumina
Salid S~te loni~ 28-20 (I 9~g) 354-357 Noah Hdl~d, Amsterdam
3 ~ E EFFECT O F T H E R M A L H I S T O R y O N ~ O F Pb(lI)-~ "-ALUMINA
IONIC C O N D U ~
Gregory S. ROHRER~ Peter K. DAVIES an~ Gregory C. FARR3NGTON ~nlofMatenal~i~a~n#n~ Unf~$lly~Pe~sfl~ni~ 3231 W,Inut S t ~ , Ph[laddphia, PA 19104,
~(~I)~"~a~um~aiscne~fsevem~div~mim~s~1he~U~fDsti~nd~nNa(I~lumin~
A~h~1h~
]3"-dum~.aha~~ much~ # t ~ d . . ~ v ~ w . Weh~vet . ~ ~ m ~heionic ~ O C l " ~ l y of ~b(ID~ "~lo~i., isvcrx s~nsifive~o
1. ]lntreductlon I n 19~2. F~I~ ngh~n and Du~n [ l ] rep olled that
li~ et M. [sJ obsr long r ~ g e 3-D order ~ d dr l ~ i n e d thai the Pb(II) ions w ~ dlSlrlbul~d nearly e w n l y belween the m O and BR sil~, The I~tr au-
all of the mobile N a ( l ) i ~ in t~e fa~t ~on ~ d ~ t~r, N~(i)-~-aIumi~a can be repla~d by a va~ety
thoB a l ~ obse~cd a p h ~ t r ~ f o ~ a t i o n at 32S'C, The ~nusual ~ n d ~ i v i l y r and r
ofdlvalcmiens, lni983,Seeve~etaL~2I~orted
~ory structural data have prompted tbls new study o f tim ionic ~nt~ucti'~ty o f Pb([[ ) . p ' - a l ~ i n a . One
the ionic ~nduc~ivity of four o f the di~lent i s ~ ~orphs o f Na(I)-p"-~lumlna (C~(It)-, St(It)-, ~a(II).,andeb(It).~"-alumlna).Overthetempera t u ~ range that was measured, the ceeMuctlvldes o f Ca(If)-, Sr ([I).,and Ba(II)~ "~lumin~ are similar, However. the ~nduefivJty o f Pb(II)-l~ "~lun~na is much higher than the other three. For example, ~t 100oc the ~nductivity ofFb(I[ )=~"~luminal* morn than 100 times gre,a t ~ than the conductivity o f
Ca( II)-, Sr(II)-, or Ba( H)-p"-alumina. In a d d i t i ~ to the anomalously high ~nducdvity, the slope of the Arrhenius plot changes n r morn temperature S e e ~ et al. ['~] suggest that a n ordor-di~rd~ int~aetion among the moMle ~ t i o n s a n d vaeanoies, which have pre~ieusly been s h ~ v n 1o influence tile ~nduetivity [31, may be responsible for this. To find a ~ a ~ n f ~ the ~omalously high a n d nonA~henius conductivity, two groups of ~ r c h e ~ investigated ihe stnlcture o f the mobile ~ t i o n sublattice. T h ~ a s r al. [4] found that the Pb(II) sublattice was dimrdered at ~ m temperature ~ d that the Fo(II) i ~ s pmdominantty occuny BE sites. Col-
p0=i~Ie~pI~natloa for theretultsd=~z~ibc~Izbovr isthattttest~r th,~fote,r o f Pb(II)-~'-alumma is vecr ~nsillve to the thormM hlsmry of the ~pte. In orc~erto test ~LS, ~ have me~ored the ~nducdvily of Pb(II)-~ "~]umiaa after diff~cnt t h e i s t treatments. Also, the vaHatlon of hint capacity wi~h temperature has b ~ n measu~d zfier d i f f e ~ t t h e i s t treatments. 2. Experimntal
No( [ )-0"~[umina r als w e ~ g m ~ by the f l ~ evaporation method previously descllbed [ 6], Single crystals were ~ t into rectangalar platelets (typi~lly 4 m m x 3 m m X0.3 ram). [qext, lhe crystals were dope ~- ~4th a radioa~ive t r ~ , ~Na. T h e Na(l)-O"-atumina ~ s then i m m ~ d in molten PbCI~ ~t 550~C i~ air. Completion of the ion exchange reaction was indicted by the reduction of the ZZNacontent in the cry*tat to background levels.
(perpendicular to the ~nductJnn plies) of ~ch crystal. Silver paint ~s then applied over the gold to ~su~ guod electric] ~ n t s c t with the platinum clcctrod~ of the conductivity cell. Conductivity measu~m~ts w~e made utter t~ diffe~ntt h a i treatm~ts, In the fi~t, c~stals ~ annealed at 400"C for 2 h, periodic measu~ments indicted that the ~ndugti~dty ~aMs ~nst~t with time at this temp~atu~. Followinga rapid cooling to ~ m lempemtu~, which was achi~ed simply by r~ovlng the crystal from a furnace ~d placing it d i r ~ t l yonto a cool metal surfa~, the grfstal was annealed at an intg~ediat v teml~ram~. The condu~ fivhy was measu~d petthdi~Uy from the start o f a n n ~ l l n guntil a ~ n s t a n t value was roached. The ~ n d u c t i v i t ywas also m ~ u r e d at 20~C in. t ~ M s as the t ~ p ~ t u ~ dr from 400 to ]00~ The ctystal was a n n ~ l c d at each tempemm ~ for 5 h or u m l i ~ appalX~tly ~ n s t a n t VM~eo f the c~ductivity w~ ~aehcd. ConduCtivity m ~ s ~ e n t s w e ~ ~ d a with an automated frequency response analysis system (Hewlatt-P~kard 4192A LF impedance analyz~ c ~ t m l l e d by a H~lett-Packard ~rles 9000 cornput.r) i n the range 100 Hz to 13 MHz. All mens u r e m ~ t s we~ p e f f o ~ e d i n a s t r e ~ o f 00wlngdry argon, H ~ t capacity m ~ u r e m c n t s w e ~ p e r t h ~ e d on a powde~d rumplemade by grindinga large (39 me) single crystal.The~ m p [ e w ~ t i n t ~ n e a l e d a t [ 30~ for 24 h and then the heat capacity was mcasu~d from ~ o m tempemlufeto 500~ at a h ~ t i n g rate o f 5 ~ m i l l - I After the ~ i n m m temperatu~ was naohed, the sample w ~ c~l~d at a rate o f 20~C rain t The i n c a s e m e n t was t h ~ immediately~p~ted. After th~ second m~suremetth the s~mple was agaln~ n e a l e d at 130~ thr 24 h befo~ the thlrd measurement w ~ made. All treatments w e ~ perth~edthsituu~derflmvingdryairvslngaSeta~ DSC i l l Culvet type differential scanning ~]orlt~tet or.
3. R ~ a l t s and d i s ~ s s i ~ Fig. 1 s h o ~ the variationof ~ n d u c t i v i t ywith ann~althg time for a ctystalrapidly~ o l e d from 400"C
~-
a ann ado ?an lOOO i zso T~ (rata.) Fi~ I. ~ r time dr of the ~ndnctivi~ of Pb(H)*~'alominaat 1 6 0 " C f o l l ~ r a p i 0 ~ o l from400"~ to r ~ m temp~aturr and then annealed at 160~ Simitar results were obtained wh~ crystals w~e annealed at t e m p c m t ~ betw~n 100 ~ d 2800C. Samp]~ annealed at higher temperatu~s ~aehcd a c ~ s t a n t conductivitystateaeterseveralhou~ while t h o ~ a n n ~ l c d at the lower tempemtu~s needed morn than a day to teach e q u l l i b d m . Below this t e m p ~ a t u ~ ~nge, the ~ n d u e f l v i t ychanged only by a smallamounL Also, a b l e this temperaturerange, the conductivity~ s ~ n s t a n t r u t h annea~ng iime. Repeated t h e ~ ] t~atments showed that the d v e~ase i n ~ n d u e l i u l t ywas reversible. Fig. 2 s h o ~ the variationo f the conductivitywith t ~ l ~ r a t u r e for Pb(ll)-I~ ~ l u m i n a . C u ~ e 1 shows the results o f measurementsmade with d e w i n g t ~ l : ~ t a t u ~ . The ~ m p l c was annealedat each ternperatu~ until the conductivityremained ~nstant. This ~ , theref~e, represents the conductivityat a n ~ equilibrinme~ditlon. Cu~e 2 s h o ~ t he initim conductivityo f the ~ m e crystal h ~ t e d to varions temp~atu~s imm~thately followinga rapid ~tingfmm4OO~ the~fore, shows the m ~ i m u m ~ n d u c t l v l ty at r temporal t~re.3"his~ i m u m value,is metastaticand o ~ a n only after mpldly ~ [ i n g the crystal from 400~c. Although these results ~ from only one crystal, they a ~ ~ p r e ~ n t a t i ~ o f ~sults obtained fi~m o t h e ~ F~g. 3 s 0 o ~ the ~sn[ts o f the ~lorlmetry expee-
( ~ 2) but appea~ again followinganother a ~ healingat 130~ (euwe 3). Thee ~sutls indi~te that the change in mnduv ti'Aty may be linked 1o a st~ctural t r a ~ f o ~ a i / o n . It is likelythat the rapid ~ o l i n g " f r ~ s " i~ a Mgh t m p ~ a ~ n m (high ~ d u u l l v J t y ) s t ~ c t u m ~ d an-
~o
9 9 (1}
duetivity) st mc~ure. A{~era~healing,tZe ~ n ~ i o n ~f~he low ~emperat~ s t m ~ r ~ to ~he Mgh ~ m peratu~ Sleet ure upon h ~ f i o g is detected ~g ~ eadoth~ [Gt m~ition.Oul~tg e4uitibrlum~oling,the change from the high tempemt~e s t ~ e m ~ m the 9 low temperature structure ~ u ~ s a change i n slope . . . . . . ~2S . . . . . . . . . . . . . i. n. .the . . . .Arrhenius ..... *,e$ ~,75 a.~s Z.7~ plot (an incr~se i n the activalion energy for ~nduction) at app~ximately 2~0'C_, The 1000/~ ae~ ~'~" mo~subtlechangeinslopeexhibitedbytherapldly F~. Z "[1terenCe~nd~r pb(ltI.[~'~am;~ ~ e I r~ r sample is probably due to imperfectquenchs~]t~whenIhe t a m ~ it ~ ~ $l~ lYfrom400~C~d cu~e 2 ing and partial ~ n v e ~ i o n to the I ~ ~ n d u e d v i t y results whenIhe~mPle~sm0i'0Yr from4O0'C state. The d e c ~ s e i n conductivitywith timethat curs for ~pldly ~ o l e d sampl~ is due to the ~ n iments.C u ~ e 1, obtainedfollowinga 24 h ~ n e a l at v e ~ i ~ o f the high temperature structure, which is 130*C, shows a broad r t~nsiliot~ bemctastable betow 280'C, to the 1 ~ temg~atum tween t30 o and 350~C that appea~ to have two structure. This t r a m f o ~ a t i o n , which ~ o t ~ur at room temperature, o~urs more and more qplckly as 2 5 0 , c i , approached. It should be pointed out that the i n e ~ i n the activationenergy for ~aduction from 0.2fl to 0.85 eV for a sample~ o l e d under n ~ u i l i h r i u m ~ n ditlons ( e u ~ e 1 of'fig. I ) o e e ~ at approximate[ v the same t c m p ~ t u r e as m e aeak o f the e e d o t h e ~ (280"C). T h ~ ~ n d u e d v i l y dat~ ~ m h l e t h e e found for the other divalentJ~~ l u m i ~ i ~ m o ~ h * [2], while c u ~ e 2 o f fig. I resemble~ the data obtained by Scorers et a]. [2] for Pb(ll)-~ ' ~ ] u m i n a in which m ~ u r e m e n t s wcrc made aftci only a l 0 minute annemlngat ~ c h tompe~tom. The structuraldifferences ohse~ed by Collinet ah [ 5] and "fhomaset M. [ 4] (i.e. ~he p y e s e n ~ and ~b~euce o f long zangc ~ f i o n - ~ n c y order, r ~ p ~ fively) may have ~ due to differen~s M the t h e ~ a l hiStory o f the ~ m p l ~ . However. the p r ~ enee or ~bsenee o f c a t i o n - v a s t y o r & d n g aloae ~s ao 1to ma 2aa zoo ~ o ~o *~o *co ~ot sufficientto a e ~ u n t for the magnitudeo f the re,~tAAru~r t'c~ t h e ~ a l tmnsHion. Fi~ 3. DSC t ~ fat pb(i [}.~,..,luml~ Cr i r ~ t e d ful. One characteristic lhat distinguishesthe Pb(II) ion iowinga 130.c aBneaLCu~e 2 ~ u h , a following a ~ i d ~ol f ~ m Ca(lI), Sr(II), and B a ( l l ) is the '~one oaiW from550'Candc u ~ 3 ~suheOaftera **and I3O~Ca~n~l, o f electrons i n its o u t e ~ o s t shell.This may explain "
iil
o
*
......
why Pb(II)-[~ ~-alum[ne is ~ differeatf ~ m C a ( l l ), S r ( l l ) . and Ba( [1)-~ "-alumina. In other o x i d ~ o f Pb(II), ~pulslonsbetween the lone pair ~ d the oxygen ions ~ s u l t i n ~ asymmetrice ~ r c U ~ o n sheIl [ 7]. The distortionsi n the ~ o r d i ~ t i o n she.lloccur to ~ d u ~ ~heCoulombic~ergy b e t ~ e n the lonepair and the llgand~ In mpldly ~ ol~'d P b ( H ) ~ "-alum l n ~ repulsionbetween the lone pair and o x y g ~ io~ ~y r Pb(II) ion Io be 1 ~ t i g h t l y b o ~ d to a p a ~ i ~ l a r sile and the~fore have a high toobility.H o o v e r , a redu~ion o f this ~puh[ve e ~ r g y as the ~ u l t o f a f ~ e ~ r k distortion~ u l d e a ~ the Pb(If) ion t ~ be m ~ tightlyb~ t ~ a par~i~ ular site and t h e e fore d ~ r the ~ d u c t i v i t y .The o b ~ a h ~ that Pb(II)-[~"-alumina does vo1 go to the 1 ~ ~ n d u c t i v l t ystate at ~ o m tcmperatur~ despite the high P b ( l l ) ion mobilityi~di~tes that the kinelics o f t ~ t r a n ~ f ~ f i o ~ depend on the toohi[ity o f the fr~ewo,'~.~ i n n s
Sn(ID-~ ~-aiumi~, 7he Sn(II) ion is k n o ~ ~c have a gre~ter lo~e pair effect than the P b ( l l ) ion.
Aeknewledgem~t This ~ s ~ h was suppor~eclby ~hc O f f i ~ OF]~'~ val R e s o r b . Additionalsupport from the National Seien ~ Foundation,Materlals Research Laboratory Program, under G ~ n t No. DMR~519059 is 8 ~ t ~ fullyacknowledged. Note added i n ~roof Subsequ~t studie~ by the autho~ have s h o ~ that lhe apparen~ p h ~ t r ~ s i t i ~ s d i ~ e d i n the paper a ~ the ~ l t o f subtle hydration r c a c t l o , Itefe~n~s
4. r It is c l ~ that t h e ~ ] historyhas ~ g~at effeeion the ion transport properties i n Pb(II)-~ "-alumina, New st~c~unl stud[~ carr/ed out uvder controlled ~ n d i t i o ~ will be n e c e ~ t y to d a t e l i n e the ~ a c t n a t u ~ o f the st~ctural cha~ge which o c ~ when Pb(ll)-13"-aluminais t r a n s f o ~ e d fi~m the hlgh conductivity star e to the Io~ c ~ d u c t [vitystate. Alsc~ ~ m e insightmay be ~ i n e d by a de~aile~lstudy o f
[11 B. Dunnand G.C. Fardngton, Mat~. R~. Bull.I5 098O) 1773. [21 l~. Seeven,J. DCNUZ21Oan~ G C Farnngt~ SolidS~te I~ 9110(1983) 146" [3] H. Sztoand R. ~kechi. J. Chem.Ph~ ~5 ([971) 677. [41 ~t.O.T~cma~M. Aldeaand G,C Fsrdnam~*S~l~ S~e ]on~ ~10 (1983)310, IS] G. C~lliu.LP. Col~b~ ~ d R. ~mc~ Sond StaleI~ics ts/l~ (t986)663. [61 LL. ~ a a l and G.C. Famn~on, J. ~Iid Sla~ Chore, 33 (zP~0)g~. [ 7] ~ E Well~St~ r ~ i~o~mcchemlsl~,5th ~ . ( Cla~~o~Press,O~fcrd,1984),, I 187.
3 ~ E EFFECT O F T H E R M A L H I S T O R y O N ~ O F Pb(lI)-~ "-ALUMINA
IONIC C O N D U ~
Gregory S. ROHRER~ Peter K. DAVIES an~ Gregory C. FARR3NGTON ~nlofMatenal~i~a~n#n~ Unf~$lly~Pe~sfl~ni~ 3231 W,Inut S t ~ , Ph[laddphia, PA 19104,
~(~I)~"~a~um~aiscne~fsevem~div~mim~s~1he~U~fDsti~nd~nNa(I~lumin~
A~h~1h~
]3"-dum~.aha~~ much~ # t ~ d . . ~ v ~ w . Weh~vet . ~ ~ m ~heionic ~ O C l " ~ l y of ~b(ID~ "~lo~i., isvcrx s~nsifive~o
1. ]lntreductlon I n 19~2. F~I~ ngh~n and Du~n [ l ] rep olled that
li~ et M. [sJ obsr long r ~ g e 3-D order ~ d dr l ~ i n e d thai the Pb(II) ions w ~ dlSlrlbul~d nearly e w n l y belween the m O and BR sil~, The I~tr au-
all of the mobile N a ( l ) i ~ in t~e fa~t ~on ~ d ~ t~r, N~(i)-~-aIumi~a can be repla~d by a va~ety
thoB a l ~ obse~cd a p h ~ t r ~ f o ~ a t i o n at 32S'C, The ~nusual ~ n d ~ i v i l y r and r
ofdlvalcmiens, lni983,Seeve~etaL~2I~orted
~ory structural data have prompted tbls new study o f tim ionic ~nt~ucti'~ty o f Pb([[ ) . p ' - a l ~ i n a . One
the ionic ~nduc~ivity of four o f the di~lent i s ~ ~orphs o f Na(I)-p"-~lumlna (C~(It)-, St(It)-, ~a(II).,andeb(It).~"-alumlna).Overthetempera t u ~ range that was measured, the ceeMuctlvldes o f Ca(If)-, Sr ([I).,and Ba(II)~ "~lumin~ are similar, However. the ~nduefivJty o f Pb(II)-l~ "~lun~na is much higher than the other three. For example, ~t 100oc the ~nductivity ofFb(I[ )=~"~luminal* morn than 100 times gre,a t ~ than the conductivity o f
Ca( II)-, Sr(II)-, or Ba( H)-p"-alumina. In a d d i t i ~ to the anomalously high ~nducdvity, the slope of the Arrhenius plot changes n r morn temperature S e e ~ et al. ['~] suggest that a n ordor-di~rd~ int~aetion among the moMle ~ t i o n s a n d vaeanoies, which have pre~ieusly been s h ~ v n 1o influence tile ~nduetivity [31, may be responsible for this. To find a ~ a ~ n f ~ the ~omalously high a n d nonA~henius conductivity, two groups of ~ r c h e ~ investigated ihe stnlcture o f the mobile ~ t i o n sublattice. T h ~ a s r al. [4] found that the Pb(II) sublattice was dimrdered at ~ m temperature ~ d that the Fo(II) i ~ s pmdominantty occuny BE sites. Col-
p0=i~Ie~pI~natloa for theretultsd=~z~ibc~Izbovr isthattttest~r th,~fote,r o f Pb(II)-~'-alumma is vecr ~nsillve to the thormM hlsmry of the ~pte. In orc~erto test ~LS, ~ have me~ored the ~nducdvily of Pb(II)-~ "~]umiaa after diff~cnt t h e i s t treatments. Also, the vaHatlon of hint capacity wi~h temperature has b ~ n measu~d zfier d i f f e ~ t t h e i s t treatments. 2. Experimntal
No( [ )-0"~[umina r als w e ~ g m ~ by the f l ~ evaporation method previously descllbed [ 6], Single crystals were ~ t into rectangalar platelets (typi~lly 4 m m x 3 m m X0.3 ram). [qext, lhe crystals were dope ~- ~4th a radioa~ive t r ~ , ~Na. T h e Na(l)-O"-atumina ~ s then i m m ~ d in molten PbCI~ ~t 550~C i~ air. Completion of the ion exchange reaction was indicted by the reduction of the ZZNacontent in the cry*tat to background levels.
(perpendicular to the ~nductJnn plies) of ~ch crystal. Silver paint ~s then applied over the gold to ~su~ guod electric] ~ n t s c t with the platinum clcctrod~ of the conductivity cell. Conductivity measu~m~ts w~e made utter t~ diffe~ntt h a i treatm~ts, In the fi~t, c~stals ~ annealed at 400"C for 2 h, periodic measu~ments indicted that the ~ndugti~dty ~aMs ~nst~t with time at this temp~atu~. Followinga rapid cooling to ~ m lempemtu~, which was achi~ed simply by r~ovlng the crystal from a furnace ~d placing it d i r ~ t l yonto a cool metal surfa~, the grfstal was annealed at an intg~ediat v teml~ram~. The condu~ fivhy was measu~d petthdi~Uy from the start o f a n n ~ l l n guntil a ~ n s t a n t value was roached. The ~ n d u c t i v i t ywas also m ~ u r e d at 20~C in. t ~ M s as the t ~ p ~ t u ~ dr from 400 to ]00~ The ctystal was a n n ~ l c d at each tempemm ~ for 5 h or u m l i ~ appalX~tly ~ n s t a n t VM~eo f the c~ductivity w~ ~aehcd. ConduCtivity m ~ s ~ e n t s w e ~ ~ d a with an automated frequency response analysis system (Hewlatt-P~kard 4192A LF impedance analyz~ c ~ t m l l e d by a H~lett-Packard ~rles 9000 cornput.r) i n the range 100 Hz to 13 MHz. All mens u r e m ~ t s we~ p e f f o ~ e d i n a s t r e ~ o f 00wlngdry argon, H ~ t capacity m ~ u r e m c n t s w e ~ p e r t h ~ e d on a powde~d rumplemade by grindinga large (39 me) single crystal.The~ m p [ e w ~ t i n t ~ n e a l e d a t [ 30~ for 24 h and then the heat capacity was mcasu~d from ~ o m tempemlufeto 500~ at a h ~ t i n g rate o f 5 ~ m i l l - I After the ~ i n m m temperatu~ was naohed, the sample w ~ c~l~d at a rate o f 20~C rain t The i n c a s e m e n t was t h ~ immediately~p~ted. After th~ second m~suremetth the s~mple was agaln~ n e a l e d at 130~ thr 24 h befo~ the thlrd measurement w ~ made. All treatments w e ~ perth~edthsituu~derflmvingdryairvslngaSeta~ DSC i l l Culvet type differential scanning ~]orlt~tet or.
3. R ~ a l t s and d i s ~ s s i ~ Fig. 1 s h o ~ the variationof ~ n d u c t i v i t ywith ann~althg time for a ctystalrapidly~ o l e d from 400"C
~-
a ann ado ?an lOOO i zso T~ (rata.) Fi~ I. ~ r time dr of the ~ndnctivi~ of Pb(H)*~'alominaat 1 6 0 " C f o l l ~ r a p i 0 ~ o l from400"~ to r ~ m temp~aturr and then annealed at 160~ Simitar results were obtained wh~ crystals w~e annealed at t e m p c m t ~ betw~n 100 ~ d 2800C. Samp]~ annealed at higher temperatu~s ~aehcd a c ~ s t a n t conductivitystateaeterseveralhou~ while t h o ~ a n n ~ l c d at the lower tempemtu~s needed morn than a day to teach e q u l l i b d m . Below this t e m p ~ a t u ~ ~nge, the ~ n d u e f l v i t ychanged only by a smallamounL Also, a b l e this temperaturerange, the conductivity~ s ~ n s t a n t r u t h annea~ng iime. Repeated t h e ~ ] t~atments showed that the d v e~ase i n ~ n d u e l i u l t ywas reversible. Fig. 2 s h o ~ the variationo f the conductivitywith t ~ l ~ r a t u r e for Pb(ll)-I~ ~ l u m i n a . C u ~ e 1 shows the results o f measurementsmade with d e w i n g t ~ l : ~ t a t u ~ . The ~ m p l c was annealedat each ternperatu~ until the conductivityremained ~nstant. This ~ , theref~e, represents the conductivityat a n ~ equilibrinme~ditlon. Cu~e 2 s h o ~ t he initim conductivityo f the ~ m e crystal h ~ t e d to varions temp~atu~s imm~thately followinga rapid ~tingfmm4OO~ the~fore, shows the m ~ i m u m ~ n d u c t l v l ty at r temporal t~re.3"his~ i m u m value,is metastaticand o ~ a n only after mpldly ~ [ i n g the crystal from 400~c. Although these results ~ from only one crystal, they a ~ ~ p r e ~ n t a t i ~ o f ~sults obtained fi~m o t h e ~ F~g. 3 s 0 o ~ the ~sn[ts o f the ~lorlmetry expee-
( ~ 2) but appea~ again followinganother a ~ healingat 130~ (euwe 3). Thee ~sutls indi~te that the change in mnduv ti'Aty may be linked 1o a st~ctural t r a ~ f o ~ a i / o n . It is likelythat the rapid ~ o l i n g " f r ~ s " i~ a Mgh t m p ~ a ~ n m (high ~ d u u l l v J t y ) s t ~ c t u m ~ d an-
~o
9 9 (1}
duetivity) st mc~ure. A{~era~healing,tZe ~ n ~ i o n ~f~he low ~emperat~ s t m ~ r ~ to ~he Mgh ~ m peratu~ Sleet ure upon h ~ f i o g is detected ~g ~ eadoth~ [Gt m~ition.Oul~tg e4uitibrlum~oling,the change from the high tempemt~e s t ~ e m ~ m the 9 low temperature structure ~ u ~ s a change i n slope . . . . . . ~2S . . . . . . . . . . . . . i. n. .the . . . .Arrhenius ..... *,e$ ~,75 a.~s Z.7~ plot (an incr~se i n the activalion energy for ~nduction) at app~ximately 2~0'C_, The 1000/~ ae~ ~'~" mo~subtlechangeinslopeexhibitedbytherapldly F~. Z "[1terenCe~nd~r pb(ltI.[~'~am;~ ~ e I r~ r sample is probably due to imperfectquenchs~]t~whenIhe t a m ~ it ~ ~ $l~ lYfrom400~C~d cu~e 2 ing and partial ~ n v e ~ i o n to the I ~ ~ n d u e d v i t y results whenIhe~mPle~sm0i'0Yr from4O0'C state. The d e c ~ s e i n conductivitywith timethat curs for ~pldly ~ o l e d sampl~ is due to the ~ n iments.C u ~ e 1, obtainedfollowinga 24 h ~ n e a l at v e ~ i ~ o f the high temperature structure, which is 130*C, shows a broad r t~nsiliot~ bemctastable betow 280'C, to the 1 ~ temg~atum tween t30 o and 350~C that appea~ to have two structure. This t r a m f o ~ a t i o n , which ~ o t ~ur at room temperature, o~urs more and more qplckly as 2 5 0 , c i , approached. It should be pointed out that the i n e ~ i n the activationenergy for ~aduction from 0.2fl to 0.85 eV for a sample~ o l e d under n ~ u i l i h r i u m ~ n ditlons ( e u ~ e 1 of'fig. I ) o e e ~ at approximate[ v the same t c m p ~ t u r e as m e aeak o f the e e d o t h e ~ (280"C). T h ~ ~ n d u e d v i l y dat~ ~ m h l e t h e e found for the other divalentJ~~ l u m i ~ i ~ m o ~ h * [2], while c u ~ e 2 o f fig. I resemble~ the data obtained by Scorers et a]. [2] for Pb(ll)-~ ' ~ ] u m i n a in which m ~ u r e m e n t s wcrc made aftci only a l 0 minute annemlngat ~ c h tompe~tom. The structuraldifferences ohse~ed by Collinet ah [ 5] and "fhomaset M. [ 4] (i.e. ~he p y e s e n ~ and ~b~euce o f long zangc ~ f i o n - ~ n c y order, r ~ p ~ fively) may have ~ due to differen~s M the t h e ~ a l hiStory o f the ~ m p l ~ . However. the p r ~ enee or ~bsenee o f c a t i o n - v a s t y o r & d n g aloae ~s ao 1to ma 2aa zoo ~ o ~o *~o *co ~ot sufficientto a e ~ u n t for the magnitudeo f the re,~tAAru~r t'c~ t h e ~ a l tmnsHion. Fi~ 3. DSC t ~ fat pb(i [}.~,..,luml~ Cr i r ~ t e d ful. One characteristic lhat distinguishesthe Pb(II) ion iowinga 130.c aBneaLCu~e 2 ~ u h , a following a ~ i d ~ol f ~ m Ca(lI), Sr(II), and B a ( l l ) is the '~one oaiW from550'Candc u ~ 3 ~suheOaftera **and I3O~Ca~n~l, o f electrons i n its o u t e ~ o s t shell.This may explain "
iil
o
*
......
why Pb(II)-[~ ~-alum[ne is ~ differeatf ~ m C a ( l l ), S r ( l l ) . and Ba( [1)-~ "-alumina. In other o x i d ~ o f Pb(II), ~pulslonsbetween the lone pair ~ d the oxygen ions ~ s u l t i n ~ asymmetrice ~ r c U ~ o n sheIl [ 7]. The distortionsi n the ~ o r d i ~ t i o n she.lloccur to ~ d u ~ ~heCoulombic~ergy b e t ~ e n the lonepair and the llgand~ In mpldly ~ ol~'d P b ( H ) ~ "-alum l n ~ repulsionbetween the lone pair and o x y g ~ io~ ~y r Pb(II) ion Io be 1 ~ t i g h t l y b o ~ d to a p a ~ i ~ l a r sile and the~fore have a high toobility.H o o v e r , a redu~ion o f this ~puh[ve e ~ r g y as the ~ u l t o f a f ~ e ~ r k distortion~ u l d e a ~ the Pb(If) ion t ~ be m ~ tightlyb~ t ~ a par~i~ ular site and t h e e fore d ~ r the ~ d u c t i v i t y .The o b ~ a h ~ that Pb(II)-[~"-alumina does vo1 go to the 1 ~ ~ n d u c t i v l t ystate at ~ o m tcmperatur~ despite the high P b ( l l ) ion mobilityi~di~tes that the kinelics o f t ~ t r a n ~ f ~ f i o ~ depend on the toohi[ity o f the fr~ewo,'~.~ i n n s
Sn(ID-~ ~-aiumi~, 7he Sn(II) ion is k n o ~ ~c have a gre~ter lo~e pair effect than the P b ( l l ) ion.
Aeknewledgem~t This ~ s ~ h was suppor~eclby ~hc O f f i ~ OF]~'~ val R e s o r b . Additionalsupport from the National Seien ~ Foundation,Materlals Research Laboratory Program, under G ~ n t No. DMR~519059 is 8 ~ t ~ fullyacknowledged. Note added i n ~roof Subsequ~t studie~ by the autho~ have s h o ~ that lhe apparen~ p h ~ t r ~ s i t i ~ s d i ~ e d i n the paper a ~ the ~ l t o f subtle hydration r c a c t l o , Itefe~n~s
4. r It is c l ~ that t h e ~ ] historyhas ~ g~at effeeion the ion transport properties i n Pb(II)-~ "-alumina, New st~c~unl stud[~ carr/ed out uvder controlled ~ n d i t i o ~ will be n e c e ~ t y to d a t e l i n e the ~ a c t n a t u ~ o f the st~ctural cha~ge which o c ~ when Pb(ll)-13"-aluminais t r a n s f o ~ e d fi~m the hlgh conductivity star e to the Io~ c ~ d u c t [vitystate. Alsc~ ~ m e insightmay be ~ i n e d by a de~aile~lstudy o f
[11 B. Dunnand G.C. Fardngton, Mat~. R~. Bull.I5 098O) 1773. [21 l~. Seeven,J. DCNUZ21Oan~ G C Farnngt~ SolidS~te I~ 9110(1983) 146" [3] H. Sztoand R. ~kechi. J. Chem.Ph~ ~5 ([971) 677. [41 ~t.O.T~cma~M. Aldeaand G,C Fsrdnam~*S~l~ S~e ]on~ ~10 (1983)310, IS] G. C~lliu.LP. Col~b~ ~ d R. ~mc~ Sond StaleI~ics ts/l~ (t986)663. [61 LL. ~ a a l and G.C. Famn~on, J. ~Iid Sla~ Chore, 33 (zP~0)g~. [ 7] ~ E Well~St~ r ~ i~o~mcchemlsl~,5th ~ . ( Cla~~o~Press,O~fcrd,1984),, I 187.