Jan 1, 1985 - associating a sodium chloride type structure (NiO) with other phases of cubic ... a eutectic, which established that lamellar structures should be ...
GROWTH OF NICKEL OXIDE - BASED ORIENTED EUTECTIC STRUCTURES AND CHARACTERIZATION OF THE INTERPHASE BOUNDARIES A. Revcolevschi, G. Dhalenne, F. D’Yvoire
To cite this version: A. Revcolevschi, G. Dhalenne, F. D’Yvoire. GROWTH OF NICKEL OXIDE - BASED ORIENTED EUTECTIC STRUCTURES AND CHARACTERIZATION OF THE INTERPHASE BOUNDARIES. Journal de Physique Colloques, 1985, 46 (C4), pp.C4-441-C4-447. .
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JOURNAL DE PHYSIQUE Colloque C4, supplement au n°», Tome 46, avril 1985
page C4-W1
GROWTH OF NICKEL OXIDE - BASED ORIENTED EUTECTIC STRUCTURES AND CHARACTERIZATION OF THE INTERPHASE BOUNDARIES A. R e v c o l e v s c h i , G. Dhalenne and F .
Laboratoire France
de Chimie Appliquée,
d'Yvoire
Université
Paris-Sud,
91405 Orsay Cedex,
Résumé - Des structures eutectiques orientées ont été élaborées par solidification dirigée dans plusieurs systèmes binaires à base d'oxyde NiO. Les directions de croissance, les relations cristallographiques entre phases eutectiques et la nature des plans d'interface ont été déterminées. Les résultats sont comparés à ceux relatifs à d'autres systèmes oxyde-oxyde. A b s t r a c t - Well aligned e u t e c t i c s t r u c t u r e s have been grown by d i r e c t i o n a l s o l i f i c a t i o n i n several n i c k e l oxide-based binary systems. Growth d i r e c t i o n s of the aligned s t r u c t u r e s , c r y s t a l ! o g r a p h i c r e l a t i o n s between the two phases of each e u t e c t i c and the M i l l e r indices of the i n t e r f a c e planes were d e t e r m i ned. The r e s u l t s are compared w i t h data r e l a t i v e to other oxide-oxide eutectics. I - INTRODUCTION
Within the framework of general studies of the structure and properties of oxide boundaries, carried out particularly on bicrystalline samples of nickel oxide /1,2,3/ we have undertaken the examination of the structure of interfaces separating two different oxide phases. Eutectic interfaces which are a good example of such phase boundaries have been considered. Directional solidification experiments were performed in several nickel oxide-based binary systems, with the object of yielding interfaces associating a sodium chloride type structure (NiO) with other phases of cubic symmetry . The systems which have been considered were : . NiO-CaO (sodium chloride) . NiO-NiAl 2 0 4 (spinel) . N i O - s t a b i l i z e d cubic ZrO„
(fluorite)
. NiO-Y 2 0 3 ( f l u o r i t e - r e l a t e d b i x b y i t e ) . The present paper reports observations on the c r y s t a l l o g r a p h y o f the aligned e u t e c t i c s t r u c t u r e s and i n t e r f a c e s which were o b t a i n e d , and compares the r e s u l t s w i t h data r e l a t i v e to other oxide-oxide systems. I I - CRYSTAL GROWTH
The directional solidification experiments were carried out by two methods. One involved a floating zone technique associated with a double ellipsoid image furnace /4,5/, in which a molten zone was established between two cylindrical rods prepared by compression and sintering : rods were rotated in opposite directions at about 60 rpm and translated at a rate of 1.5 cm.h" 1 . The other technique is the "skull method" /6/, consisting of r.f. direct induction Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985449
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h e a t i n g o f batches o f about 500 grams contained i n a copper-cooled c r u c i b l e about 5 cm i n diameter and 6 cm high. Preheating o f the powder m i x t u r e s was achieved by using chunks o f metal corresponding t o one o f t h e oxides. A f t e r m e l t i n g , t h e c r u c i b l e c o n t e n t was s l o w l y c ~ o l e d ~ y i e l d i ndgi r e c t i o n a l s o l i d i f i c a t i o n a t a r a t e o f about 6 mm.h-'. S t a r t i n g powders were h i g h p u r i t y oxides ( > 99.9 %) mixed i n t h e p r o p o r t i o n s i n d i c a t e d i n Table I.These p r o p o r t i o n s a r e s l i g h t l y d i f f e r e n t from those i n d i c a t e d by t h e phase diagrams/7,8,9/'and were determined by m e t a l l o g r a p h i c examination. I n t h e part i c u l a r case o f NiO-calcium s t a b i l i z e d Zr02, no phase diagram was a v a i l a b l e . Theref o r e a systematic study o f v a r i o u s m i x t u r e s o f NiO, Zr02 and CaO was c a r r i e d out, t h e p r o p o r t i o n s o f t h e l a s t two oxides being chosen i n a manner t o correspond t o a Zr02-15 mol % CaO-stabilized c u b i c z i r c o n i a : t h e b e s t r e s u l t s i.e. r e g u l a r e u t e c t i c s t r u c t u r e s and absence o f primary phases were obtained f o r t h e composition 70 mol % Ni0-25.5 % Zr02-4.5 % CaO.
Fig. 1- Transverse s e c t i o n of NiO-Zr02 e u t e c t i c d i r e c t i o n a l l y s o l i d i f i e d a t 1.5 cm.h-I. Well a l i g n e d e u t e c t i c s t r u c t u r e s were observed i n a l l f o u r systems under study(Fig.1) the e u t e c t i c phases and t h e i r l a t t i c e parameters being those r e p o r t e d i n Table I. S t r u c t u r e s are l a m e l l a r f o r NiO-CaO, NiO-Zr02 and NiO-Y203 ; t h i s o b s e r v a t i o n i s i n good agreement w i t h c a l c u l a t i o n s /10,11/ r e l a t i v e t o l a m e l l a r - t o - r o d t r a n s i t i o n s i n a e u t e c t i c , which e s t a b l i s h e d t h a t l a m e l l a r s t r u c t u r e s should be s t a b l e when t h e minor component has a volume f r a c t i o n h i g h e r than 0.3. I n t h e case o f Ni0-NiA1204, i n s p i t e o f volume f r a c t i o n s o f 0.42 f o r N i O and 0.58 f o r NiA1204, f i b e r type a l i g n e d structures were obtained. Such anomalies have been observed i n o t h e r systems e.g. MgO-CaO /12/ b u t have n o t been w e l l explained so f a r . 111
-CRYSTALLOGRAPHIC
RELATIONS
Microfragments o f t h e d i r e c t i o n a l l y s o l i d i f i e d samples o r i e n t e d along t h e growth d i r e c t i o n were s t u d i e d by r o t a t i n g c r y s t a l , Weissenberg ( F i g . 2) and Buerger precession methods t o determine p r e f e r r e d growth d i r e c t i o n s and e p i t a x i a l r e l a t i o n s . The patt e r n s revealed t h a t growth d i r e c t i o n s have low M i l l e r i n d i c e s and t h a t p r e c i s e and simple o r i e n t a t i o n r e l a t i o n s e x i s t between the two phases (Table I ) . The i n f o r m a t i o n concerning growth d i r e c t i o n s o f t h e e u t e c t i c phases o b t a i n e d from these m i c r o f r a g ments was confirmed by X-ray d i f f r a c t o m e t r y experiments c a r r i e d o u t on l a r g e t r a n s verse s e c t i o n s o f s o l i d i f i e d i n g o t s : h i g h i n t e n s i t y peaks corresponding t o planes normal t o growth d i r e c t i o n s were observed.
Fig. 2 - Weissenberg zero l e v e l photograph normal t o [001] o f Zr02 and [110] o f NiO showing t h e para1 1e l ism o f [100]Tro2 and [lll]\iO. To s p e c i f y t h e M i l l e r i n d i c e s of t h e interphase planes i n t h e case o f l a m e l l a r styuct u r e s a s p e c i a l procedure was a p p l i e d f o r t h e NiO-CaO and NiO-Y20 e u t e c t i c s 113,141. Fragments o f t h e d i r e c t i o n a l l y s o l i d i f i e d samples having a morpho?ogy which was p r e v i o u s l y i d e n t i f i e d by o p t i c a l observation and X-ray d i f f r a c t i o n , were placed on a Table I - C r y s t a l l o g r a p h i c r e l a t i o n s a t the l a m e l l a r i n t e r f a c e s . NiO
CaO
40 mol % CaO
E u t e c t i c composition E u t e c t i c phases S t r u c t u r e type --
-
-
NiO
Y203
31 mol % Y203
NiO
CaO
NiO
NaC1
NaCl
NaC1
Y203
NiO
A1203
14 mol % A1203 NiO
NiA1204
P;::iO NaCl
-
-
MgA1204
NiO
-
Zr02(CaO)
70 mol % NiO NiO
Zr02
NaCl
CaF2 5.12
-
~
Lattice parameter of the eutectic phases(A)
4.20
Growth d i r e c t i o n
Epitaxial relationships
(hkl )//(hkl)
I n t e r f a c e plane
(111)
4.75
4.18
10.60
4.19
8.07
4.18
(hkl)
I/( h k l )
[lie] I/ [ o o ~ ] (111) I/ (100)
(111)
(111)
(100)
fibers
[lie] /I [ o o ~ ] (111) 11(100) (111)
(100)
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Fig. 3 - Computer simulation of the atomic arrangement a t the NiO-Y203 interface, viewed perpendicularly to the growth direction and showing the mating of three-fold and four-fold symmetry surfaces. The same crystallographic relationship i s observed f o r the NiO-Zr02 eutectic. goniometer head and observed by S.E.M. The orientation of the lamellae was estimated micrographically from t h e i r intersection with the surfaces of the fragments : i n t e r faces are (111) f o r both NiO and CaO phases in the NiO-CaO system and ( 1 1 1 ) ~ i oand (100)y203for the NiO-Y203 system. The method could not be applied so f a r t o the NiOZr02 eutectic but considering the identical epitaxial relations found f o r both NiOY2O3 and NiO-ZrOp systems, and the very close crystallographic structures of Zr02 and Y2O3 (cubic zirconia has a f l u o r i t e type structure, and yttrium oxide has a bixbyite type structure which may be described as a f l u o r i t e superstructure obtained by ordering of oxygen vacancies on the anionic s u b l a t t i c e ) i t i s likely t h a t the interface planes are and (100)zro2 in NiO-Zr02. Additional arguments tending t o confirm t h i s will be discussed l a t e r in t h i s paper. Fig. 3 represents a computer simulation of the atomic arrangements corresponding t o such an epitaxy between four-fold and three-fold symmetry surfaces in the particular case of NiO-Y203. IV
-
INTERFACE STRUCTURES
Considering the data presented in Table I , i t i s interesting to represent the structures of the oxides involved in lamellar eutectics, perpendicularly t o growth direct i o n s , in order to describe atomic arrangements near the interfaces (Fig. 4 ) . In the case of the NiO-CaO eutectic made of nickel oxide and calcium oxide solid solutions,the interface can be easily described by (111) alternate planes of metal and close-packed oxygen : the metal planes are richer in nickel on one side of the interface and in calcium on the other side since we deal with solid solutions (Fig. 4a). The distances between anionic planes in each phase d i f f e r only s l i g h t l y . In the case of the NiO-Y203 eutectic where there i s no detectable s o l u b i l i t y of one oxide in the other, a description of the interface in terms of oxygen and metal planes
NiO -CaO
I
NiO-Y203, /
r
*
NiO- Z r 0 2
\
F i g . 4 - R e p r e s e n t a t i o n o f t h e NiO-CaO i n t e r f a c e and o f t h e atomic l a y e r s o f YpO3, N i O and Zr02, viewed p e r p e n d i c u l a r l y t o growth d i r e c t i o n s ( i . e . p a r a l l e l t o i n t e r f a c e s ) . may a l s o be considered ( F i g . 4 ) . T h i s d e s c r i p t i o n i s complicated by t h e f a c t t h a t i n b i x b y i t e t h e oxygen vacancy d i s t r i b u t i o n d e f i n e s two d i f f e r e n t c r y s t a l l o g r a p h i c p o s i t i o n s f o r y t t r i u m atoms and one s e t o f oxygen s i t e s i n the cubic s t r u c t u r e /15/ : along a d i r e c t i o n , atoms are n o t s t r i c t l y coplanar and d e f i n e e i t h e r planes o r "sheets" ( F i g . 4b) /14/. Because o f t h e existence o f two d i f f e r e n t types o f c a t i o n i c l a y e r s i n Y203, t h r e e d i f f e r e n t a l t e r n a t i v e forms o f e p i t a x y can be considered i n r e l a t i o n a t t h e i n t e r f a c e . We o r d e r t o s a t i s f y the observed (100)y203 / / have shown t h a t t h e most probable i n t e r f a c e s t r u c t u r e would be t h a t i n which a n i c k e l oxide oxygen plane would be f o l l o w e d by an y t t r i u m plane, i t s e l f f o l l o w e d by an y t t r i a type oxygen sheet /14/ : t h i s s t r u c t u r e i s t h e o n l y one i n which t h e s i x - f o l d c o o r d i n a t i o n observed f o r Y i n YpO3 i s maintained. We s h a l l a l s o note t h a t i n both NiO and YpO3 phases, the distances between two consecutive metal-oxygen l a y e r s , a l o n g . t h e d i r e c t i o n perpendicular t o t h e growth d i r e c t i o n , a r e v e r y near one another. The a n a l y s i s o f t h e NiO-Zr02 i n t e r f a c e seems e a s i e r because o f t h e s i m p l e r f l u o r i t e s t r u c t u r e o f Zr02,viewed p e r p e n d i c u l a r l y t o i n F i g . 4d : one would have a t the i n t e r f a c e successively, zirconium, oxygen and n i c k e l planes. O f course t h i s rough d e s c r i p t i o n does n o t take i n t o account t h e small d i s t o r t i o n s associated w i t h t h e vacancies i n t r o d u c e d i n t h e Zr02 oxygen s u b l a t t i c e by t h e calcium oxide w h i c h s t a b i l i z e s t h e cubic m o d i f i c a t i o n o f z i r c o n i a . Here again we s h a l l note t h a t i n both N i O and ZrOp phases the distances between two consecutive metal-oxygen l a y e r s along t h e d i r e c t i o n perpendicular t o the growth d i r e c t i o n , a r e n o t very d i f f e r e n t . V
-
DISCUSSION
Our r e s u l t s b r i n g a d d i t i o n a l data t o the already l a r g e v a r i e t y o f c r y s t a l l o g r a p h i c c h a r a c t e r i s t i c s determined f o r n o n - m e t a l l i c e u t e c t i c s . Obviously i t appears t h a t i n b i n a r y s t r u c t u r e s i n v o l v i n g phases o f cubic symmetry, t h e , < I l l > and growth d i r e c t i o n s p r e v a i l . T h i s i s t r u e f o r the systems mentioned i n t h i s study b u t a l s o f o r Mg0-MgA1204, MgO-cubic Zr02 and MgO-CaO where growth d i r e c t i o n s are < I l l > f o r a l l phases /12/. This was a l s o observed i n sodium c h l o r i d e - t y p e h a l i d e e u t e c t i c s T h i s holds a l s o f o r t h e f l u o r i t e - t y p e phases o f such as NaCl-NaF and LiF-NaF /16,17/. t h e ZrO Ln203 (Ln = Nd, Sm, Dy) e u t e c t i c s /18/ and f o r the cubic Zr02 phase o f the e u t e c t i c /12/, which a l l grow along .
z~o~-c~Z;O~
When comparing growth d i r e c t i o n s i n s t r u c t u r a l l y homologous systems, we f i n d i t hard
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t o make g e n e r a l i z a t i o n s : ifwe n o t e a good agreement between data r e l a t i v e t o t h e NaC1-spinel type systems Ni0-NiA1204 and Mg0-MgA1204 /19/, on t h e o t h e r hand, i n t h e case o f N a C 1 - f l u o r i t e type systems, we f i n d t h a t the s i m i l a r r e s u l t s concerning NiOY 0 and NiO-Zr02 d i f f e r from those proposed by M i n f o r d e t a1 /20/ f o r MgO-Zr02 where < f l j > M g O / / Zr~2. Discrepancies e x i s t a l s o among t h e NaC1-NaCl type systems where 1 // 1~, 1 // 11 and 1 // 11 r e l a t i o n s have been found /12,17/. Generalizations seem a l s o d i f f i c u l t when c o n s i d e r i n g t h e e p i t a x y r e l a t i o n s r e p o r t e d SO far f o r non-metal1 i c systems, p a r t i c u l a r l y f o r l a m e l l a r s t r u c t u r e s . It seems however t h a t a l a r g e p a r t of t h e data f i t w i t h t h e w e l l accepted concepts o f m i n i m i z a t i o n o f l a t t i c e m i s f i t s and balance o f charge d e n s i t i e s a t t h e i n t e r f a c e s . These f a c t o r s would p l a y a major p a r t i n t h e establishment o f i n t e r f a c e planes and r e l a t i v e o r i e n t a t i o n s o f t h e l a t t i c e s o f t h e two phases. Considering t h a t i n l a m e l l a r o r i e n t e d s o l i d i f i c a t i o n , i n t e r f a c e s a r e para1 l e l t o growth d i r e c t i o n s , growth axes should be d i r e c t i o n s o f s t r o n g atomic bonding o r more p r e c i s e l y o f " p e r i o d i c bond chains" 1211 contained i n the i n t e r f a c e plane. Hence i n one such plane a very l i m i t e d number of growth d i r e c t i o n s m i g h t be p o s s i b l e , among which, as seen so f a r i n most systems, o n l y one would p r e v a i l ; o t h e r would be p o s s i b l y s t a b i l i z e d by l o c a l p e r t u r b a t i o n s d u r i n g t h e growth process, o r by i m p u r i t i e s . This seems t o be confirmed by observat i o n s made on t h e NiO-Zr02 e u t e c t i c f o r which,besides t h e major growth axes i n d i c a t e d i n Table I we have found on microfragments o r i e n t e d a l o n t h e growth d i r e c t i o n and s t u d i e d by t h e Weissenberg method, a growth d i r e c t i o n [2Q11Ni0 // [ 0 1 3 ] ~ ~T ~ h i s~ . relationship
i s equivalent,wi t h i n a few minutes precision, t o [IT01 NiO
// [001] zro2
proposed i n Table I and i n d i c a t e s t h a t r e l a t i v e l a t t i c e o r i e n t a t i o n s a r e t h e same i n t h i s fragment and i n t h e b u l k ; i t confirms a l s o t h e above-made assumpt i o n concerning t h e i n t e r f a c e plane i n NiO-Zr02 which i s c l e a r l y d e f i n e d i n each phase by two growth d i r e c t i o n s : t h a t o f t h e fragment and t h a t o f t h e b u l k e u t e c t i c m a t e r i a l . We s h a l l a l s o note t h a t t h e r a t h e r unusual [103]zr02 growth a x i s we have determined, has been q u i t e s y s t e m a t i c a l l y observed on p o l y c r y s t a l l i n e c u b i c s t a b i l ized z i r c o n i a i n t h e course o f a r e c e n t study o f the r e l a t i o n between morphology and s t r u c t u r e i n s t a b i l i z e d Zr02 /22/.
-
VI
CONCLUSION
C r y s t a l l o g r a p h i c r e l a t i o n s and i n t e r f a c e planes have been determined f o r several oxide-oxide e u t e c t i c systems and add t o t h e i n f o r m a t i o n from which i n a near f u t u r e g e n e r a l i z a t i o n s should be made. To improve t h e present d e s c r i p t i o n o f e u t e c t i c cryst a l l o g r a p h i c r e l a t i o n s h i p s and i n t e r f a c e s i t w i l l be i n t e r e s t i n g t o apply t o these b i n a r y systems t h e c o i n c i d e n t s i t e l a t t i c e theory. High r e s o l u t i o n e l e c t r o n microscopy, 1a r g e l y used t o day f o r g r a i n boundary studies, should a1so improve o u r understanding o f t h e two-phase type i n t e r f a c e s discussed i n t h i s paper. REFERENCES
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