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STRUCTURAL STUDIES OF THE LIQUID Rb-RbBr SYSTEMS BY XANES
J. Jal, J. Dupuy, A. Sadoc
To cite this version:
J. Jal, J. Dupuy, A. Sadoc. STRUCTURAL STUDIES OF THE LIQUID Rb-RbBr SYSTEMS BY XANES. Journal de Physique Colloques, 1986, 47 (C8), pp.C8-799-C8-802.
�10.1051/jphyscol:19868153�. �jpa-00226056�
JOURNAL DE P H Y S I Q U E
C o l l o q u e C 8 , suppl6ment au n o 12, Tome 47, dgcembre 1986
STRUCTURAL STUDIES OF THE LIQUID Rb-RbBr SYSTEMS BY XANES
J . F. J A L , J. DUPUY and A . SADOC'
Departement de Physique des Materiaux, Universite Claude Bernard, F-69622 Villeurbanne Cedex, France
'LURE ( C N R S , C E A , M E N ) , Batiment 2090, Universite Paris-Sud, F-91405 Orsay Cedex, France
R e s u m e
- Une e t u d e XANES d u s e u i l d ' a b s o r p t i o n K d u b r o m e e s t r e p o r t e e p o u r l e s y s t e m e f o n d u Rb/Rb%r e n f o n c t i o n d e l a c o n c e n t r a t i o n .
A b s t r a c t
- A XANES s t u d y a b o v e t h e B r
K
a b s o r p t i o n e d g e o f t h e m o l t e n Rb/RbBr s y s t e m i s r e p o r t e d v e r s u s c o n c e n t r a t i o n .I - INTRODUCTION
A l a r g e a m o u n t o f w o r k h a s a l r e a d y b e e n d e v o t e d t o t h e s t r u c t u r a l i n v e s t i g a t i o n of m e t a l - m o l t e n s a l t s o l u t ' i o n s . A s a m a t t e r o f f a c t t h e m o l t e n s a l t m i x t u r e p r o b l e m p r o v i d e s a n e x c e l l e n t t e s t i n g g r o u n d f o r t h e o r i e s o f l i q u i d s . R e c e n t l y , a n e u t r o n i n v e s t i g a t i o n 1 o f t h e s t u c t u r a l o r d e r i n Rb, (Rb B r ) l - x s o l u t i o n s h a s s h o w n h o w l i t t l e t h e s h o r t r a n g e c o r r e l a t i o n s o f t h e p u r e s a l t a r e p e r t u r b e d b y t h e a d d i t i o n o f m e t a l , e v e n u p t o a b o u t 40 % m e t a l . On t h e o t h e r h a n d f o r t h e m e t a l r i c h s i d e , t h e i n t r o d u c t i o n o f s m a l l a m o u n t s o f s a l t c o n s i d e r a b l y a l t e r s t h e p u r e m e t a l s h o r t r a n g e c o r r e f a t i o n s . A d i f f e r e n t a p p r o a c h i s t a k e n h e r e b y s t u d y i n g t h e Rb-RbBr s y s t e m v e r s u s c o n c e n t r a t i o n u s i n g XANES. A p r e l i m i n a r y r e p o r t
h a s y e t b e e n m a d e f o r Rbom8(RbBr) 0 . 2 . I1 - EXPERIMENT
Rb,(RbBr)l-, s a m p l e s w e r e p r e p a r e d f o r x= 0,O. 1 , 0 . 2 , 0.4, 0.5, 0.6, 0 . 8 b y s p u t t e r d e p o s i t i o n o n t h e w i n d o w s o f a h i g h t e m p e r a t u r e c e l l . S i l i c a w a s c h o s e n f o r t h e s e w i n d o w s i n o r d e r t o a v o i d t h e s t r o n g c h e m i c a l r e a c t i v i t y o f t h e m a t e r i a l s a n d d u e t o i t s t r a n s p a r e n c y i n t h e X - r a y d o m a i n
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19868153
C8-800 JOURNAL DE PHYSIQUE
Each s i l i c a window was 0 . 5 mm t h i c k ; t h i s was a c o m p r o m i s e f o r thinner, windows have t h e d i s a s t r o u s t e n d e n c y t o c r a c k d u r i n g t h e heating ( o r even b e f o r e !) and t h i c k e r windows a b s o r b m o r e of t h e X - r a y beam.
The experiments w e r e c a r r i e d out a t LURE (DCI) w i t h t h e EXAFS - 1 s p e c t r o m e t e r u s i n g a Si (220) c h a n n e l c u t m o n o c h r o m a t o r . The EXAFS s p e c t r a of RbBr w e r e m e a s u r e d v e r s u s t e m p e r a t u r e f r o m r o o m t e m p e r a t u r e up t o t h e m e l t i n g p o i n t (T, = 692 "C). F o r l i q u i d Rbx (RbBr)l-,, t h e s p e c t r a w e r e t a k e n above t h e m e l t i n g p o i n t (Tm
-
631 "C - 670 " C f o r x v a r y i n g f r o m 0 . 8 t o 0.1). Both t h e B r (13 475 ev) and Rb (15 201 ev) K-
a b s o r p t i o n edges w e r e r e c o r d e d one a f t e r a n o t h e r but up t o now we h a v e j u s t a n a l y z e d t h e B r edge.The n o r m a l i z e d
x
(k) o s c i l l a t i o n s f o r RbBr a r e p l o t t e d i n f i g u r e 1 a t r o o m t e m p e r a t u r e and i n t h e l i q u i d state, at 700 " C . The e f f e c t of t h e r m a l d i s o r d e r shows up i m m e d i a t e l y since, a t 7 0 0 " C , t h e o s c i l l a t i o n s d e c r e a s e v e r y r a p i d l y v e r s u s t h e e n e r g y s o t h a t t h e y c o m p l e t e l y d i s a p p e a r about 150 - 2 0 0 eV above t h e edge. T h e r e f o r e a XANES (X-ray A b s o r p t i o n n e a r Edge S t r u c t u r e ) s t u d y was n e c e s s a r y f o r t h e s e l i q u i d s y s t e m s .The F o u r i e r t r a n s f o r m s (FT) of t h e k ~ ( k ) s p e c t r a w e r e done using t h e same window (10-190 eV) f o r a l l t h e c o n c e n t r a t i o n s ( f i g u r e 2). They e x h i b i t m a i n l y one peak i n t e n s i t y and p o s i t i o n of which do not v a r y much i n a l l t h e d o m a i n of c o n c e n t r a t i o n s (0.1
-
0.8). T h e r e f o r e t h e l o c a l o r d e r a r o u n d a B r atom appears a l m o s t i d e n t i c a l w h a t e v e r t h e c o n c e n t r a t i o n may be. This c o r r o b o r a t e s t h e n e u t r o n d i f f r a c t i o n s t u d y .and EXAFS s p p e c t r a above t h e B r edge i n RbBr c o m p a r e d (a) i n t h e s o l i d s t a t e a t r o o m t e m p e r a t u r e (a) and (b) i n t h e l i q u i d s t a t e at 700°C
0 .'
. .
**-...$ , .'.* .,*. E:.~- ..-;.;+. . . ,..r-.
1 - 2%.-..
4F i a u r e 1 . E x p e r i m e n t a l XANES
F i g . 2 C o m p a r i s o n of t h e F o u r i e r t r a n s f o r m s o f k ) ~ ( k ) f o r l i q u i d RbBr and f o r d i f f e r e n t c o n c e n t r a t i o n s x of l i q u i d Rbx (RbBr)! -x.
A d e t a i l e d a n a l y s i s o f t h e m a i n peak has been done f o r l i q u i d RbBr and Rbo.8 (RbBr)0.2. The peak-was i s o l a t e d and b a c k t r a n s f o r m e d i n t o k space w h e r e t h e i n v e r s e FT was f i t t e d using t h e s i n g l e s c a t t e r i n g f o r m u l a . The r o o m t e m p e r a t u r e s p e c t r u m of p u r e RbBr was u s e d as a r e f e r e n c e t o e x t r a c t e x p e r i m e n t a l a m p l i t u d e s and p h a s e s h i f t s and t o d e t e r m i n e t h e r e l a t i v e v a l u e of t h e d i s o r d e r p a r a m e t e r o.
The m a i n peak was f o u n d t o be due t o Rb b a c k s c a t t e r e r s at s i m i l a r d ~ s t a n c e I n l i q u i d RbBr and Rbo,8 (RbBr)0,2. The n u m b e r of Rb n e l g h b o u r s c a n be e v a l u a t e d r o u g h l y t o be about 6
*
0 . 5 i n t h e p u r e s a l t ( A o = 0.20+
0 . 0 3 A) and 4
*
0.5 i n t h e m i x t u r e ( A o = 0.11*
0 . 0 3 A). A s km i s about 1.5 A-I and o about 0 . 2 5 A, t h e c r i t e r i o n k m o t l i s f u l f i l l e d (kmo I 0.37). T h ~ s c r i t e r i o n e s t i m a t e s t h e m i n i m u m a c c e s s i b l e p h o t o e l e c t r o n k v a l u e f o r w h i c h t h e d e t e r m i n a t i o n o f t h e f i r s t s h e l l i s a l l o w e d i n h ~ g h l y d i s o r d e r e d m a t e r i a l s w i t h o u t t a k i n g i n t o account any m u l t i p l e s c a t t e r i n g e f f e c t .We a r e now a n a l y z i n g t h e Rb edge i n o r d e r t o s t u d y t h e e f f e c t o f t h e s a l t a d d i t i o n t o t h e m e t a l s t r u c t u r e .
JOURNAL DE PHYSIQUE
R e f e r e n c e s 1 - CHABRIER
,
G., J A L , J.F, CHIEUX, P., DUPUY, J . ,P h y s . L e t t . S A (1 9 8 2 ) 47.
2- J A L , J . F , DUPUY, J., SADOC, A . , J. P h y s . C o l l o q u e
a,
SUPPI n o - 1 2 (1985) 1 0 7 .3- STERN, E . A . , P h y s i c s o f d i s o r d e r e d m a t e r i a l s , e d . b y D . A . ADLER, H.
FRITZCHE a n d S. R. OVSHINSKY, P l e n u m p r e s s ( 1 985)
