MECHANISM OF THE SOLID STATE FORMATION OF LEAD ZIRCONATE TITANATE

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MECHANISM OF THE SOLID STATE FORMATION OF LEAD ZIRCONATE TITANATE

E. Jarén, P. Durán

To cite this version:

E. Jarén, P. Durán. MECHANISM OF THE SOLID STATE FORMATION OF LEAD ZIRCONATE TITANATE. Journal de Physique Colloques, 1986, 47 (C1), pp.C1-537-C1-542.

�10.1051/jphyscol:1986181�. �jpa-00225612�

JOURNAL DE PHYSIQUE

Colloque C 1 , suppl6ment au n 0 2 , Tome 47, f 6 v r i e r 1986 page c1-537

MECHANISM OF THE SOLID STATE FORMATION OF LEAD ZIRCONATE TITANATE

E.

JARBN

^{and P.} D U R ~ N

Instituto d e Ceramica y Vidrio, C.S.I.C., Dpto. d e Materiales CerAmicos Especiales, Arganda del Rey, Madrid, Spain

Resum6

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Les r e a c t i o n s 2 i ' B t a t s o l i d e q u i o n t l i e u p e n d a n t l a c a l - c i n a t i o n de m a t e r i a u x ceramiques d e t y p e PZT o n t 6 t 6 6 t u d i 6 e s s u r deux d i f f e r e n t e s c l a s s e s de m a t i s r e s p r e m i s r e s . On p r o p o s e un nou- veau mgchanisme pour La r g a c t i o n d e f o r m a t i o n d e s s o l u t i o n s s o l i - d e s du t y p e PZT.

Abstract

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The s o l i d phase r e a c t i o n s which o c c u r d u r i n g t h e c a l c i - n a t i o n of PZT c e r a m i c s have been s t u d i e d on two k i n d of raw mate- r i a l s . A new mechanism r e a c t i o n f o r t h e PZT s o l i d s o l u t i o n s forma- t i o n i s proposed.

I

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INTRODUCTION

I n an a t t e m p t t o c l a r i f y t h e r e a c t i o n s o c c u r r i n g i n t h e PZT f o r m a t i o n c e r a m i c s , many p a p e r s have been a d r e s s e d t o such a n o b j e c t i v e by a num- b e r of r e s e a r c h e r s / I / - / 6 / . I n a g e n e r a l manner t h e r e s u l t s r e p o r t e d b y t h e major c o n t r i b u t o r s c o i n c i d i n a c c e p t i n g t h a t t h e l e a d t i t a n a t e (PT) i s t h e f i r s t r e a c t i o n p r o d u c t t o b e formed when t h e mix-ed o x i d e s t e c h - n i q u e were used / I / , / 2 / , / 5 / , / 6 / . However, i f a s u b m i c r o n . z i r c o n i a pow- d e r c h e m i c a l l y p r e p a r e d i s used t h e n t h e PZ f o r m a t i o n i s p r e v i o u s t o t h e PT f o r m a t i o n / 4 / . T h i s PZ i n t e r m e d i a t e p r o d u c t was n o t o b s e r v e d i n t h e m a j o r i t y of o t h e r p a p e r s , w i t h t h e o n l y e x c e p t i o n of Ohno e t a 1 /7/who a l s o r e p o r t e d t h e PZ f o r m a t i o n which s u b s e q u e n t l y r e a c t s w i t h P T t o form PZT s o l i d s o l u t i o n . On t h e o t h e r hand, Yamaguchi e t a 1 / 8 / r e p o r t t h e p o s s i b l e f o r m a t i o n of PZ b u t o n l y under d e t e r m i n e d c o n d i t i o n s . The p r e - s e n c e of an i n t e r m e d i a t e PbO s o l i d s o l u t i o n was r e p o r t e d by S p e r i / 9 / , and confirmed l a t e r by Hankey / l o / .

I t seems obvious t h a t t h e PZT c a n be s y n t h e s i z e d by t h e s o l i d s t a t e r e - a c t i o n PbO+Zr02+Ti02 + PZT, and t h a t t h i s r e a c t i o n c a n n o t proceed i n on- l y one s t e p . I n t h e powder m i x t u r e of t h e o x i d e s r e a c t a n t s t h r e e t y p e s of i n t e r g r a n u l a r c o n t a c t p o i n t s a r e t o e x i s t , where t h o s e i n t e r m e d i a t e p r o d u c t s w i t h t h e lower f o r m a t i o n h e a t w i l l be f i r s t l y formed, which t h e n r e a c t s f u r t h e r t o form t h e PZT s o l i d s o l u t i o n a s t h e f i n a l r e a c t i o n p r o d u c t . The o b j e c t i v e of t h e p r e s e n t work was u n d e r t a k e n t o s t u d y t h e e f f e c t of r e a c t i o n t e m p e r a t u r e , t i m e and powder r e a c t i v i t y i n o r d e r t o d e t e r m i n e t h e k i n e t i c s and mechanism of t h e PZT s o l i d s t a t e f o r m a t i o n .

I1

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EXPERIMENTAL PROCEDURE

The m i x t u r e s were made from c r y s t a l l i n e raw m a t e r i a l s w i t h h i g h p u r i t y

~ b 0 2 9 9 . 9 % ( o r t h o r h o m b i c m a s s i c o t )

,

~ i 0 2 2 9 9 . 9 % ( t e t r a g o n a l a n a t a s e )

,

and

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986181

C 1 - 5 3 8 JOURNAL DE PHYSIQUE

~ r 0 ~ 2 9 9 . 8 % (monoclinic b a d d e l e y i t e ) , 1.5% Hf0, included. To study t h e e f f e c t of Z r O z r e a c t i v i t y on PZT formation, an amorphous Zr02 o b t a i n e d by p r e c i p i t a t i n g t h e hydroxide with ammonium from a ZrOC1,.8H20 aqueous s o l u t i o n was used. The complex zirconium hydroxide was f u r t h e r c a l c i n e d a t 5 0 0 ' ~ f o r s e v e r a l hours. Average p a r t i c l e s i z e was measured f o r a l l powders using a C o u l t e r Counter, and s p e c i f i c s u r f a c e a r e a measurements were c a r r i e d o u t by BET technique using N 2 a s an a b s o r b a n t . I n o r d e r t o determine which i s t h e f i r s t r e a c t i o n product t o be formed d u r i n g t h e PZT formation, a DTA/TGA technique was u t i l i z e d w i t h A1,0, a s a r e f e - rence m a t e r i a l .

A PZT composition w i t h Zr/Ti/53/47, which i s c l o s e d t o t h e phase boun- dary, was chosen. Powder were mixed i n s t o i c h i o m e t r i c r a t i o s i n a b a l l m i l l ?or 4 hours w i t h alumina b a l l s g r i n d i n g media i n a c e t o n a , and t h e s l u r r i e s were d r i e d a t 50°C. The oxides mixture was r e m i l l e d by a t t r i - t i o n f o r 1 hour and d r i e d . A f t e r d r y i n g t h e powders were p r e s s e d a t 1 0 0 MPa i n t o p e l l e t s 5 mm i n diameter and 4 mm t h i c k . These p e l l e t s were placed i n a s m a l l platinum c r u c i b l e and s u b j e c t e d t o r e a c t i o n tempera- t u r e i n a preheated f u r n a c e . The h e a t - t r e a t m e n t s were c a r r i e d o u t i n a i r a t a f i x e d temperature between 500° and 850°C. Above 750°C t h e pe- l l e t s were placed i n a s e a l e d platinum c r u c i b l e t o avoid t h e evapora.

t i o n of l e a d oxide. A f t e r s u b j e c t i n g t h e samples t o t h e d i f f e r e n t reac- t i o n temperatures, t h e y were a i r quenched and grounded i n an a g a t a mor- t a r .

The phase composition of t h e r e a c t i o n p r o d u c t s was determined by X-ray d i f f r a c t i o n a n a l y s i s with a P h i l i p s d i f f r a c t o m e t e r u s i n g CuKa r a d i a t i o n and a n i c k e l f i l t e r . Although t h e PbO-Zr02-TiO, i s a very complex sys- tem, however t h e d i f f e r e n t phases formed d u r i n g t h e PZT formation a r e c h a r a c t e r i z e d by a good symmetry and, t h e r e f o r e , t h e i n t e n s i t y o f t h e d i f - f r a c t i o n l i n e s could be taken t o do an approximate e s t i m a t i o n of t h e r e - a c t i o n p r o g r e s s . I n t h i s way, t h e e q u a t i o n x i = K I i / I o i was used t o c a l - c u l a t e t h e approximate c o n c e n t r a t i o n of t h e d i f f e r e n t phases ( x i = p h a s e c o n c e n t r a t i o n , I i = i n t e n s i t y of t h e d i f f r a c t i o n l i n e f o r t h e phase i i n t h e r e a c t i o n p r o d u c t , I o i = i n t e n s i t y f o r t h e same d i f f r a c t i o n l i n e i n t h e pure phase, and Kzconstant)

.

The d i f f r a c t i o n l i n e s ( 1 1 1 )

,

(1 1 1 )

,

( I O I ) , (122) and (111) f o r PbO, Z r O , , TiO,, PbTiO,, PbZrO, and PZT r e s - p e c t i v e l y were used. I n t h e c a s e of t h e PZT phase, i t s r e l a t i v e concen- t r a t i o n was e s t i m a t e d by r e f e r e n c e t o a s t a n d a r d prepared from a compo- s i t i o n Pb ( Z r . , , T i . , ,) 0 , s i n t e r e d a t 1230 OC.

I11

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^{RESULTS AND} DISCUSSION

Fig. 1 shows t h e DTA curves o b t a i n e d f o r t h e two kind of PZT samples prepared. For mixed o x i d e s sample, i n which t h e average p a r t i c l e s i z e a f t e r a t t r i t i o n m i l l i n g was < 2 pm, an exothermic peak a t about 560°C, a t t r i b u t e d t o t h e PT formation, was observed. Asecond thermal e f f e c t a t approximately 7 4 0 ' ~ was a l s o found. I n t h i s c a s e t h e endothermic peak must be a t t r i b u t e d t o t h e PZT formation which i s a n e n d o t h e r m i c p r o c e s s . For t h e sample i n which a Z r O 2 chemically prepared was used, t h e DTA curve only shows an endothermal e f f e c t a t approximately 750°C which i s r e l a t e d t o t h e PZT formation, and no exothermic peak was observed. The s e r e s u l t s a r e q u i t e d i f f e r e n t t o t h o s e found by C h a n d r a t r e y a e t a l / 3 7 who a t t r i b u t e d t h e endothermic peak t o t h e PZ formation which compound was, on t h e o t h e r hand, n o t observed i n t h e i r X-ray d i f f r a c t i o n e x p e r i ments. Hankey and Biggers /2/ found a complex DTA curve i n which t h e PT formation was an endothermal e f f e c t . A second endothermic peak a t - t r i b u t e d t o t h e PbO s o l i d s o l u t i o n formation was a l s o r e p o r t e d . F u r t h e g more, a t h i r d peak, endothermic, i n t h i s c a s e corresponding t o t h e PZT formation was a l s o r e p o r t e d . A t p r e s e n t time t h e DTA curves from Han- key and Biggers /2/ a r e d i f f i c u l t t o be i n t e r p r e t e d with c l e a r n e s s .

Fmm mixed oidn

From amorphous 2% PZT

TEMPERATURE (*C)

F i g . 1 . - DTA p l o t s f o r t h e two t y p e s o f s a m p l e s .

A s p r e v i o u s l y mentioned, t h e complete q u a n t i t a t i v e a n a l y s i s of t h e pha s e s composition d u r i n g t h e PZT formation would be extremly d i f f i c u l t t o o b t a i n . However, a s shown i n Fig. 2 an e s t i m a t i o n of t h e phase com- p o s i t i o n i n t h e r e a c t i n g mixture a s a f u n c t i o n of temperature was made a s follows:

From mixed oxides

A s e t of p r e l i m i n a r y experiments with o x i d e mixtures of composition Pb(Zr.,,Ti.,,)O, showed t h a t a f t e r h e a t i n g a t 500°C f o r s e v e r a l hours t h e p r o d u c t s c o n t a i n PbO, Zr02, TiO, and t r a c e s of PbTiO,, which i n d i - c a t e s t h a t below 5 0 0 ' ~ t h e r e a c t i o n proceeds o n L y a t i n t e r g r a n u l a r P b 0 - T i O , c o n t a c t s according t o t h e f o l l o w i n g equation:

PbO + T i O , + PbTi0,

to

09 From mlxed oxldes

0 06

, o

* 0 4

TEMPERATURE ("3 TEMPERATURE

F i g . 2 . - Phase c o m p o s i t i o n o f t h e r e a c t i n g m i x t u r e a s a f u n c - t i o n o f t e m p e r a t u r e .

This r e a c t i o n was completed a t approximately 6 0 0 ' ~ a s shown by t h e d i - sappearance of t h e X-ray d i f f r a c t i o n l i n e s corresponding t o T i O , . AS t h e temperature was i n c r e a s e d a very important f e a t u r e w a s o b s e r v e d between 600 and 6 5 0 ' ~ . In t h a t narrow temperature range t h e r e a c t i o n simultaneously proceeds a t i n t e r g r a n u l a r PbTi03-PbO and PbTi0,-ZrO, c o n t a c t s , and some of PbO and Zr0, d i f f u s e s i n t o t h e l e a d t i t a n a t e pe- r o v s k i t e l a t t i c e t a k i n g p l a c e t h e r e t h e formation of a l e a d t i t a n a t e s o l i d s o l u t i o n . This assumption was supported by t h e observed i n c r e a s e f o r t h e l a t t i c e parameters of t h e l e a d t i t a n a t e compound. On t h e o t h e r

JOURNAL DE PHYSIQUE

hand, n e i t h e r d i f f r a c t i o n l i n e s of t h e l e a d z i r c o n a t e compound n o r PbO s o l i d s o l u t i o n f o r m a t i o n were o b s e r v e d . F u r t h e r m o r e , t h e i n t e n s i t y of t h e d i f f r a c t i o n l i n e s f o r l e a d t i t a n a t e d i d n o t s h i f t , a n d t h o s e c o r r e s ponding t o t h e PbO and Zr02 o x i d e s s l i g h t l y d e c r e a s e s . T h e r e f o r e , the- second r e a c t i o n s t e p t a k i n g p l a c e b e f o r e PZT f o r m a t i o n i s : PbTiO,

+ +

PbO

+

Z r O , ^a ( P b T i 0 , ) s s .

Beyond 650°C, t h e s a t u r a t e d l e a d t i t a n a t e s o l i d s o l u t i o n a c t s a s a sup- p o r t f o r t h e PZT f o r m a t i o n . I t seems p r o b a b l e t h a t t h e d i f f u s i o n of p b 2 + and Z r w i o n s i n t h e l e a d t i t a n a t e p e r o v s k i t e s u r f a c e which r e - s u l t s i n t h e f o r m a t i o n of PZT was more f a v o u r a b l e . Although t h e d i f f u - s i o n i n t h e PbO-Zr02 c o n t a c t p o i n t s t o g i v e PZ i s n o t improbable,

however t h a t compound was n o t d e t e c t e d i n t h e l e a d s t e p of t h e PZT r e a c - t i o n s y n t h e s i s . I t i s p o s s i b l e t h a t t h e d i f f u s i o n r a t e f o r t h e pb2+ and

z r 4 +

i o n s i n t o t h e l e a d t i t a n a t e ss p e r o v s k i t e l a t t i c e was h i g h e r t h a n t h a t f o r t h e f o r m a t i o n of PZ.In t h i s way,the f i n a l r e a c t i o n i n t h e PZT f o r m a t i o n c a n b e e s t a b l i s h e d a s f o l l o w s : (PbTiO,) ss

+

^PbO

+

^{Z r O , + (PZT) ss}

From Zr02 c h e m i c a l l y p r e p a r e d

Taking i n t o a c c o u n t t h a t t h i s o x i d e i s t h e l e a s t r e a c t i v e of t h e t h r e e o x i d e s m i x t u r e , a submicronized Zr02 w i t h a h i g h s p e c i f i c s u r f a c e (149 m2/g) f o r t h e s e e x p e r i m e n t s was used. A s c a n b e s e e n f r o m F i c j . Z , P ~ T ~ O , i s always t h e f i r s t r e a c t i o n p r o d u c t t o b e formed and two s t a g e s of t h e r e a c t i o n may c l e a r l y b e d i s t i n g u i s h e d : a i n i t i a l p e r i o d i n which p r a c t i c a l l y a l l t h e PbTi0, i s formed a n d , b e f o r e t h i s r e a c t i o n was f L n i s h e d , s t a r t s t h e PbZr0, f o r m a t i o n . That r e a c t i o n sequence t a k e s p l a c e between 450' and 6 0 0 ' ~ . T h e r e f o r e , t h e r e a c t i o n o c c u r r i n g i n t h a t t e m p e r a t u r e r a n g e p r o g r e s s mainly i n t h e i n t e r q r a n u l a r c o n t a c t s PbO- T i 0 2 w i t h t h e PbTi03 f o r m a t i o n , and can b e d e s c r i b e d by t h e e q u a t i o n : PbO

+

T i 0 2 + PbTi03.However t h i s r e a c t i o n s t e p was n o t d e t e c t e d by DTA

( s e e F i g . I ) , p r o b a b l y due t o r a p i d PZ f o r m a t i o n and i t s s i m u l t a n e a o u s i n t e r a c t i o n w i t h PT t o g i v e PZT.

The s u b s e q u e n t r e a c t i o n t a k i n g p l a c e i s t h e PbZrO, f o r m a t i o n which i s formed i n t o a narrow t e m p e r a t u r e r a n g e ( 6 0 0 ' - 6 5 0 ' ~ ) . I n t h a t tempera- t u r e i n t e r v a l more t h a n 70-80% of PbZrO, i s formed a s it c o u l d be e s t i mated from t h e i n t e n s i t y of t h e d i f f r a c t i o n l i n e s . B e f o r e t h e maximum f o r m a t i o n of PbZrO, a d e c r e a s e i n t h e i n t e n s i t i e s o f t h e P b T i 0 , d i f f r a c t i o n l i n e s was o b s e r v e d , which i s r e l a t e d w i t h t h e b e g i n i n g o f t h e f o r mation of t h e PZT s o l i d s o l u t i o n . The r e a c t i o n i n t h i s second s t e p c a n b e d e s c r i b e d a s f o l l o w s : PbO

+

Zr02 + PbZrO,.

T h i s r e a c t i o n , a s c a n be o b s e r v e d i n F i g . 2 , t a k e s p l a c e a t a h i g h e r r a t e t h a n t h e r a t e f o r t h e PbTiO, f o r m a t i o n .

I n t h e f i n a l s t e p , t a k i n g p l a c e from 650' t o 8 5 0 ° c , t h e PbZrO, i s con- sumed more r a p i d l y t h a n t h e PbTiO,, which i s r e l a t e d t o a lower s t a b i - l i t y of t h a t compound a s t h e t e m p e r a t u r e i s i n c r e a s e d . On t h e o t h e r hand, it was found t h a t t h e r e a c t i o n - r a t e f o r t h e PZT f o r m a t i o n was lower t h a n i n t h e c a s e i n which a mixed o x i d e s was u s e d . Then t h e f i - n a l s t e p c o u l d be d e s c r i b e d by t h e e q u a t i o n : PbTi0,

+

PbZrO, + (PZTIss.

From t h e above d e s c r i b e d r e s u l t s t h e f o l l o w i n g r e a c t i o n mechanism f o r t h e PZT f o r m a t i o n c o u l d be advanced. I n t h e f i r s t s t e p , above 4 5 0 ° c , r e a c t i o n p r o c e e d s a t t h e h i g h e r r a t e which r e s u l t s i n t h e t o t a l c o n s u m p t i o n of T i 0 2 . When t h e PT f o r m a t i o n was completed some of PbO and Z r O , o x i d e s r e a c t s f u r t h e r , a l m o s t immediately, w i t h t h e formed PT t o g i v e a PT s o l i d s o l u t i o n a s a r e s u l t of t h e second s t e p r e a c t i o n . When t h e PT was s a t u r a t e d and i f t h e t e m p e r a t u r e i s i n c r e a s e d t h e n t a k e s p l a c e t h e t h i r d s t e p , w i t h t h e i n t e r a c t i o n of PbO, Z r O 2 and T i 0 2 i n t h e i n t e r i o r of t h e PT p e r o v s k i t e m a t r i x forming t h e PZT s o l i d s o l u t i o n a s t h e f i n a l p r o d u c t of t h e r e a c t i o n . According t o o u r r e s u l t s i t seems r e a s g n a b l e t o assume t h a t t h e PT p e r o v s k i t e l a t t i c e a c t s a s a h o s t m a t r i x i n which t h e i n t e r d i f f u s i o n of t h e

z r 4 + ,

p b 2 + and ~ i & + i o n s f a v o u r e t h e PZT f o r m a t i o n . I n t h i s way t h e PZT s y n t h e s i s e f f i c i e n t l y p r o c e e d s a t

approximately 8 0 0 although the complete formation is only acheived ~ ~ ~ at higher temperatures. This fact could be explained by assuming the formation of thick layers of PZT between the grain of the reactant pro ducts which probably hindered the mass-transport..If this is so, the diffusion-rate of 2r4+ and pb2+ ions in the PT host matrix could bethe rate-limiting step in the final PZT solid solution formation.

When a ZrO, with a high surface energy was used, the kinetics for the PZT formation was strongly affected, and a new intermediate reaction product, PZ, was formed. Such an intermediate reaction product was al- ways formed after the PT reaction formation was practically completed,

F i g . 3 . - R e a c t i o n scheme f o r t h e PZT f o r m a t i o n .

and never previously to the PT formation as reported by Venkataramany and Biggers /4/. This could depend of the reactivity of the ZrO, pow- der. This seems reasonable as the formation enthalpy for PT is lower than that for the PZ formation. It this case the reaction mechanism for the PZT formation could be described by a first step reaction in which, as always, the PZ is formed. Due to the high reactivity o c ZrOE a new intermediate reaction product, the lead zirconate, is for- med in the second step reaction. When these two compound have been formed begins the PZT formation at the PT/PZ interfaces as the third step reaction. It is believed that the diffusion-rate in the PT/PZT and PZ/PZT interfaces could be the rate-limiting step in the forma- tion of a PZT solid solution. Fig. 3 shows schematcaly the two reac- tion systems leading to the PZT formation.

According to our results a new reaction mechanism for the solid state PZT formation is proposed. The differences foundwithrespecttothe re- action mechanism reported by other authors may be due to the different experimental conditions, however the conclusions here attained are ba- sed on the experimental results obtained on oxides mixtures carefully prepared. Although became very difficult to delimit the begining and the end of each step reaction, however the present results can contri- bute to elucidate the reaction phenomena which occur during the calci- nation in the PZT ceramics fabrication.

REFERENCES

/I/. Matsuo

Y.

and Sasaki

H. J.

Amer. Ceram. Soc., 48(1965)289.

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/3/. Chandratreya S.S., Fulrath R.M. and Pask J.S.

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64 (1981)442.

C1-542 JOURNAL

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PHYSIQUE

/ 4 / . V e n k a t a r a m a n y S. a n d B i g g e r s J . V . A m e r . C e r a m . S o c . B u l . , 5 9 ( 1 9 8 0 ) 4 6 2 .

/ 5 / . K i n g o n A . I . , T e r b l a n c h e P.'J. a n d C l a r k J . B . , C e r a m i c s I n t e r n . , 8 ( 1 9 8 2 ) 1 0 8 .

/6/. H i r e m a t h B.V., ~ i ' n ~ o n A . I . and B i g g e r s J . V . J. Arner. C e r a m . S o c . , 6 6 ( 1 9 8 3 ) 7 9 0 .

/ 7 / . O h n o T., T a k a h a s h i M. a n d T s u b o u c h i N. J . J a p a n S o c . P o w d . M e t a l l 2 0 ( 1 9 7 3 ) 1 5 4 .

/8/. Y a m a g u c h i T . , S h o S . H . , M a k o m o r i M. a n d K u n o H. C e r a m u r g i a I n t . , 2 ( 1 9 7 6 ) 7 6 .

/ 9 / . ~ p e r i V.M., P h . D. T h e s i s , R u t g e r s U n i v e r s i t y , N e w B r u n w i k , N J , 1 9 6 9 . ( 1 0 / . K a n k e y D . L . , Ph. D. T h e s i s . T h e P e n n . S t a t e U n i v . U n i v e r s i t y P a r k .

1 9 8 0 .