ssbauer spectroscopic study of nonstoichiometric ... - Springer Link

Hypcrfirm Interactions 69 (1991) 879-882

879

MOSSBAUER SPECTROSCOPIC STUDY OF NONSTOICHIOMETRIC PEROVSKITE, Ba,_ ~Ca FeO3_a Kiyoshi NOMURA, Yasuhiro SUGAWARA, Hong Ling LI and Yusukc UJIHIRA FaculO, of Engineering, Tile UniversiO, of Tokyo, Itongo 7-3-1, Bunkyo-ku, Tokyo, 113 J(tl)alr Nonstoi(:hiometrie l)erovskites, lira ~Ca~IreO:~ ~. w e r e prepared by a pyrolysis o r Lhe m i x L u r e o f lia. Ca tIll(l Ire o i l . r a t e s . The amounL o r o x y g e u ( l e r i ( : i e n ( : y i n c r e a s e s wil, h l, he inere;i.'-;e o r Ca eolll,enL. A new IllglgllCI.ic sl)e(:ies was o b s e r v e d at. roolll t.(:llll)(':l':l/.llre ill Ni(i.(-;s[):ltl(':r s i ) c c L r : l o r If:if x C a , I;('():i ~ . I L Is SUpllose(l l, haI, Lhe i r o n s p e ( : i e s wou Id o c ( : i l l ) y all i n L e r m e d i a L e sILe o f o c L a h e d r a i arld Lel, r a h e d r a l coordinaLlons. 1.

Illtrodu(:tioII

I)erov.'.-;k i t . e , Keller;ll ly f'Ol'lntl l a l . e ( ] as AI}():~ ,,, , i .'-; o l l e o[" t h e Ino.sL aLt. r;tetive J e l l :lll(] e l e . e t , r i e a l corlcluel, ive lnaterials /1/. Froln tile view poJnl, s or (:l-ygL;ll Iog;ri].phi(:;iI sI. r u e t u r e ;llld electrical (:ondueLivi Ly, l.he I.yl) i ( : a l I)erovski Los, Sr~ ~ l , a ~ l : e ( ) ~ a n d srlreO:~ ~ , h a v e been well eh;lrael, erized I)eeau,'-;e ( : h a I - K e e o n l l ) e r l s a l , i o n o r I,'e( I I I ) i s a c h i e v e d I)y t.he (.'real, ion or oxygen vae;:trl(:ies, resulting the coexisl, ence or Ire(Ill) and I"e(IV) ill Lhe c o I n l ) o l l l l ( I s / 2 / . I)erovski to shows high ('ondueLivi Ly due Lo oxygen ion gr:msl)or Lag ion in i.he erysl.al and serves as

eat.alysl.

For

t.he oxiclation

o[' hydroearl)on

and

al il)Imt,ie a l c o h o l

/31.

T h e ( : a t ; . l l y t . i(" a ( : L i v i Ly w a s v.,'el I ( : o r r e l ; l l . e d t.o Lhe d i f ' r e r e n ( : e or the inLerat.omie (lisLanee rrom Lhe e q u i l i b r i u m disL;ince /4/. 't'eraok;l el, al ./5/ reported their tile p;lrtiil[ s;ubsLil.uLion o[" A s i L e and iI s i t e (rations (:h:lnged oxygen semipernleabi I i Ly i n ],n('oO:} l);l,,:;e(I p e r o v s k i L e . Ir r'oln the telnl)era gu re deperldellce o[' l.he l';l Lc o F oxygen p e r l ] l e a t i Oll through L a ~ 6 A ' n . 4C, o a . RI:el~. ~():~ , i t was concluded 1.haL the oxygen semiperln(mbi I il.y increased wil.h the order or A'=l}a>('a>gr. 'rhe~ o r d e r oF oxyffell selnil)ermeabi I I Ly i s ( ' o n s i d e r e d Lo l)e r e l a L e d to tile di rrererlee or ionic radius beLweell sub,sl, i L u L e d ;llkal ine e a r l , h tllel,:II iol|.q a n d [,a a' It sugKesLs that Life s y s L e l n a L i ( " .'.;t,u(ly o r p e r o v s k i L e l)repared I)y Lhe substitution of A s i Le i o n s with (li ff'erent ionic radit]s and the same valence (Ca ~' =0.099 nm, Ba 2 ' = 0 . 1 3 ( ; nm) g i v e s n e w .'-;lleeies. "]'ire authors describe several results obl,ai ned I)y Lhe M(sssbauer spectroscopic arl:l]yges o | ' }}:ll - x C a , lreOa ~ ,q3'sl, elll. 2.

Experimenta.

I deLails

Samples were prepared I)y a pyrolysis o[" the m ixt.ure oF mel, a l (I}a,Ca, i l l l d I,'e) e i t r a g e s Col)recipi tated in t.he p r e s e n c e or eLhyleue Kly(:ol. The mixed tiLl-aLes were preheated ill "-'100C Lo lll;llz.e ii p g / s l , e , L h e l l h e i l l , e d Lo 2 0 0 " C r o t 5 h, 500 C for 5 h , r i n d 8 5 0 " C I ' o r 10 h . T h e .r were Lhen pulverized and t)re..'.-;sed lille pel let.'.;, rol lowed Ily Lhe hea. g i IlK : l g : l i n a t 1000 C for 24 h . lie r o t e measu r inK Mossllauer s l ) e c t. r a , each .q;llll l) I e w a s a n n e a I e d ;}. L 7 0 0 " C [ ' o r 4 h a n d c o o I e(I .'.-;I o w I y ill rtll'llnee. AIt, horIKh the erystnl strucLure or lia i l e r o v s R i Le is t, et. r a g ; o n a l , a n d Ca p e r o v s k i t e is rhombie, the erysLal]oKraphy o[" t, he praeti(::tl samples (]eperl(Is on the oxygen derieien(:y. Snl;ll I p e a k s or rllombi(: structure (a=0.57, b=O.(;3 itrld c = l . 4 1 l l m ) wits observed ill X r a y (li r g ' r a e L i O l l 1)atLerns or the mixLure o r lln a r i d (7,a l ) e r o v . q k i I . e s . Oxygen eorlLellL.'..; w e r e deLerlllJlle(J I)y a n i o ( ] o m e L r y :lll(I :1 t h e r l l l i l l Kl';lVilllei;ry. ]ll oFder go colnl);IFe tile d i I'rerence between Llle bll I k n r l d Lhe surface, conversion electron i',l(~;ssbauer spectra (CI':MS) w e . r e m e a s u r e d b y IIIOtJllLill.t5 Lhe sample powder o n a.n a l u m i n i t n n sheeL w i. Lh c a r b o n paste.

~) J.C. Baltzcr A.G., Scicnlific Publishing Company

880 3.

K. Nomura el al. / M.S. of nonstoichiometric perovskite Bas_,. Ca., FeOs_ ~ and

ResulLs

discussion

IVl6ssbauer spec:Lra of I~a~ , ( ; a , l , ' e O . - ) ~ a r e shown in (:ig.] . Three i{i;iI~lle 1, [ C CO[llpOllellLN ll[ld (.wo (lotll) I (: (.s w e r e observed i Ii L h ( ; s e s l ) e ( : L r a . . T w o in;iKilel, i c COllli)Oll(;llLs wel'(': C O l l V e l l | . i O l l ; l ] l y a s s l g l l e d Lo ]FOIl s p e c i e s i n o ( : l ; , l h e c l r l l I (lIl(] t . e t r ; l h e d r n l ( ~ o o r d i [lilI, i o11~ . T w o ( ] o u b l e l ; s w e r e c l u e 1;o I)III-IIIII;IKII('~I.i(~ I"e( I I I ) ;lIItl I " e ( I V ) Sl)e(:ies o(:(:III)NIIIK II i o n s i (.e wi I.h disordered del'icienL oxygens. The in(:v'e;lse o [ ' Cil (:oIIL(:IIL d e c r e a s e d I)IIF;IIIIIIKIleI. i c I , ' e ( I V ) COlllpoilell|.N illl(I i l l c ' r e ; l . ~ e d I.WO III~I~Ilel. iC C O m l ) o l l e n l ; s because oxyt-cei) d e f ' i ( : i e i l ( : y increased wi Lh I.he i n c r e a s e o[" C a c o l i L e n L . [rrespecglve oF Lhe Ca coilLeliL , a new illagllc g i c sexLeL wiLh lnLorniedial.c hylierl'ine Fields was observod ill the N{)ssbnuer Sl)ecLra oF al I lillxLilros of l l a l , C a , l,'eO.~ ~ The coi/['igilragioil o[' oxygen atoms ;lrOlili(l [lip. ] r o l l al.Oln i s h i gh l y tle. l ' o r n l e d I)y Lho d i l ' P e r e n l , alliOlllll; o f oxygoil. M(Jssl)aiier l)aralllOLOrs F o r I}ai , C a , l,'o()a ~ ; l r o shoWll i l l V i g . 2. I~lagnei. i(: ( ' O m l ) o n e n i . s w e r e d u e Lo t . h r o e I,'e( I I I ) S l ) C ( : i e s . iS wllues of In,'IKn(.~Lic compolielll.s ill ocLahedral s i Lo (0.3511111i/s) alld illLormediaLo lihase ( 0 . 1 71ilIII/S) d e ( : l ' e a s e d llll(] i l l ( : r e l l s e ( I w i l.h I.lie i l i ( : r e a s e o[" o x y g e n def'iciell(:y, respe(:Llvely, whcroas IS v a l u e s o f ill~lgliOL[C COlllpOllOnt; i n Legrahodral siLe (0.|'7111111/S) k e p L llllllOSL ( ' o r l s L a l i g . i 9

"

|

|

i

'

i

-

9

i

T

, i! f (a)

'

(el

b~ i. 4-)

t

i

I

i

i

84

!J (r

'

" I

I

',(~)

i

,[

',

[

V

,

'

-6

i

'

-4

L

-Z

0

(h)

'

9

2

4

I

,

6

8

VOIOCILy

t.

,

9

-8

,

'

I t

|

-6

[

,

'I!!/ VVl;

(d) -8

I

"

-4

-2

I

l

0

,

'

2

4

,oi

~'I"

I

I

,

6

8

(ram/s)

I:ig.1 IH{~ssbauer spectra ()f I/;ll-~C;l~l:cOr) ~i. (;i) x = 0 . 0 5 , (b) x=0.1, (c) x=O.15, (d) x=0.2, (e) x=0.4, (f) x=O.G, (g) x=0.8, (h) x = l

K. Nomura el al. / M.S. of nonstoichiometric perovskite Bat_.,. Ca.,. leO_,_ ,~

881

The increase oi" o x y g e n ( ] e r i ( : i e n c y decreased the absolul.e QS value.,.; o[" o(:t,~d1(,.dral s i L e ;]nd i H t o r l n e ( J i a L e s i Le,'.-;, whCl'O;l:.4 i I, i l l c r c ' n s c d QS o r teLrahedral site. Irifluence oi" i o ~ l i c r a d i u s of" s u b s t , i L u t e d A siLe ions on laLLice consl.ant., oxygen dericiency, nnd elecLricnl c o u d u c l , i v i Ly were invesLigaLed in the case or l,al - ~ ( ; a ~ . , , ~ , ~ l ] a ~ . 4 5 ~ l , ' e o a . . ~ by l.he comparison with [,a1-.Sr. VeO3-~/6/. l]ecause a small ionic radius l,'e(IV) might (lesLroy 1.he e q u i l i b r i u m under Lhe coexistence o f I]a "~' a n d C a 2 ' , oxygen deficiency Is considered to increase in a synLhetic binary subsLit.uLed perovs;ki Le, Three hYl)errine m a g r l e l , i(: f'iel(Is or iron oc,(:upyin~ ocl.;dmdrnl , LeLrahedt-al ;ul(l i n t e r m e ( l i ; l l . e siLes we:re n l ) o u l . 5 0 . 5 , 43.2, and 47.5 T, resl)ecl, ively. M;ib[nel. i(." c,")Inl)OllC~li[..'.-; o[" l , e l . r ; l h ( ' . ( I r ; t l nnd o(:I.;di(;(Irnl s i l,es (:;tiRe J'r()[ll t h e o r ( J e l ' i l l b ~ o[" o x y l . [ C l l ( J ( ~ r i c i ( ~ r l c y IIlOI'C l.h;lll ~3:().:L~ ;ll, rOOlll LCH]II)('}.F;I ill PC , T h e IIC'W i rOll s l ) e c i e s .'-;howed n .'--;pi II O I ' ( } C I " i I I ~ e V C I I i II l.he (lisord(:rinl.7 region o[' def'i(:icnL ox.yg(ms oc(:urrcd in oct,;thedral ;rod teLr;lhe(lra.I si Les. When nil mn~rmLic rields ir~cre;~se(l sl ighl. ly wil.h I.he i n c r e ; ~ s e o[" the oxygen dericien(:y, the hylmrrine st. rucLure o1" I.he I } a , - , C n , l"e0.~ became c I ose Iy mmJ ogous 1,o tim L o r brownm i I I e r ite, (;;W'e()e ~, ( ocLaheclral si Le: IS=0.341nnul/s, qS=-0.27tullUl/S, Ili , , : 5 1 . 4 T ;lllCJ 1.el. r n h e d r n l S i {.O.: IS=0. ]7111|11/S, QS=0.:}SI|illI/S, [li ,, = 4 3 . 8 T / 7 / ) . ] |. i S esLilll;l[.(~(l I"t'