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Submitted on 1 Jan 1985
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INFLUENCE OF STRUCTURAL AND TEXTURAL
CHANGES ON THE LIGHT SCATTERING
SPECTRUM OF THE ELECTROLYTE GLASS
(LiCl)x(H2O)1-x
J. Pelous, A. Essabouri, R. Vacher
To cite this version:
I N F L U E N C E OF STRUCTURAL AND T E X T U R A L CHANGES ON T H E L I G H T SCATTERING
SPECTRUM OF T H E ELECTROLYTE GLASS ( L ~ C ~ ) ~ ( H ~ O ) ~ - ~
J . P e l o u s , A . E s s a b o u r i a n d R. V a c h e r
Laboratoire de Science des Mate'riaux Vitreux (U. A. 11 1 9 / , Uniuersite' des
Sciences e t Techniques du Languedoc, Place E . BataiZZon,
34060 MontpeZZier Cedex, France
Resume
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Nous p r e s e n t o n s des mesures obtenues p a r d i f f u s i o n R a y l e i g h - B r i l l o u i n m e s melanges ( L i C l ) x ( H 2 0 ) 1 - x . Pour x = 0 , l,
nous avons & t u d i @ le s p r e - m i e r s stades de l a c r i s t a l l i s a t i o n p a r des mesures d ' i n t e n s i t e en f o n c t i o n du temps de t r a i t e m e n t au v o i s i n a p e de Tq. Le comportement observe correspond 2 un processus de c r o i s s a n c e des m i c r o c i i s t a u x . Nous presentons egalement l e s r e s u l t a t s c o n c e r n a n t l a v i t e s s e des hypersons dans des s o l u t i o n s v i trogenes de d i f f e r e n t e s c o n c e n t r a t i o n s . On observe l ' i n f l u e n c e d ' u n processus r e l a x a - t i o n n e l p o u r l e s p l u s orandes c o n c e n t r a t i o n s a i n s i que l e s anomalies de v i - t e s s e c a r a c t e r i s t i q u e s de 1 'e a u surfondue.A b s t r a c t
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R a y l e i g h - B r i 1 lo u i n s c a t t e r i n g measurements have been p e r f o r m e d i n 7 ~ ~ X ~ H ~ O ) 1 - x.
The f i r s t s t a g e o f c r y s t a l l i z a t i o n , d u r i n ? h e a t t r e a t m e n tnear Tg, . i n v e s t i g a t e d b y i n t e n s i t y measurements vs t i m e f o r x = 0.1, shows a b e h a v i o u r c o m p a t i b l e w i t h a r i p e n i n g mechanism. We p r e s e n t a l s o h y p e r s o n i c v e l o c i t y r e s u l t s i n t h e g l a s s - f o r m i n g s o l u t i o n s f o r v a r i o u s c o n c e n t r a t i o n s . The r e l a x a t i o n a l process a p p a r e n t f o r h i p h e r c o n c e n t r a t i o n s and t h e anomalous v e l o c i t y v a r i a t i o n c h a r a c t e r i s t i c o f s u p e r c o o l e d w a t e r a r e discussed.
Glasses formed f r o m aqueous s o l u t i o n s o f t h e e l e c t r o l y t e L i C l have two i n t e r e s t i n a c h a r a c t e r i s t i c s : g l a s s e s can be o b t a i n e d f r o m s o l u t i o n s i n a v e r y l a r p e c o n c e n t r a - t i o n range and p a r t i a l r e c r y s t a l l i z a t i o n can be a c h i e v e d and e a s i l y c o n t r o l l e d by h e a t t r e a t m e n t n e a r t h e g l a s s t r a n s i t i o n t e m p e r a t u r e Tg.
M a i n l y f o r t h e above reasons, t h e system has been e x t e n s i v e l y s t u d i e d i n t h e r e c e n t p a s t y e a r s . The phase diagram has been determined ( 1 ) b y c a l o r i m e t r i c experiments and t h e s t r u c t u r e has been i n v e s t i g a t e d i n t h e 1 i q u i d phase ( 2 ) and i n t h e amorphous phase when c r y s t a l l i z a t i o n occurs (3), by n e u t r o n s c a t t e r i n g . On t h e o t h e r hand, a c o u s t i c s t u d i e s a t u l t r a s o n i c ( 4 ) and h y p e r s o n i c f r e q u e n c i e s ( 5 ) have shown t h e e x i s t e n c e o f t u n n e l 1 in g s t a t e s c h a r a c t e r i s t i c o f ? l a s s e s a t l o w temperature. The va- r i a t i o n o f t h e d e n s i t y o f s t a t e s o f t h e d e f e c t s w i t h t e m p e r a t u r e and Tg has been d i s c u s s e d ( 5 ) i n t h e framework o f t h e f r e e volume model ( 6 ) . The comparison o f t h e e x p e r i m e n t a l r e s u l t s w i t h t h e t h e o r e t i c a l p r e d i c t i o n s shows t h a t t h i s model i s n o t s u f f i c i e n t t o d e s c r i b e t h e 1 ow t e m p e r a t u r e b e h a v i o u r . However, t h e c o n c e n t r a t i o n de- oendence o f t h e d e n s i t y o f s t a t e s suggests t h a t t h e l o w temperature anomalies a r e n o t independent o f t h e a c o u s t i c p r o p e r t i e s above Tg. The i d e a t h a t t h e e x i s t e n c e i n t h e l i q u i d o f s t r u c t u r a l u n i t s , which a r e quenched a t Tg, determines t h e p r o p e r t i e s o f t h a g l a s s i s v e r y a t t r a c t i v e and needs t o be c o n f i r m e d by f u r t h e r i n v e s t i n a t i o n s . I n t h i s way, a b e t t e r knowledge o f t h e ~ i c r o s c o p i c d e t a i l s o f t h e d i s o r d e r can be expected.
The experiments were performed i n t h e r i g h t - a n g l e s c a t t e r i n g geometry, u s i n g a con- v e n t i o n a l pressure-scanned double-pass Fab y P e r o t i n t e r f e r o m e t e r . The s o u r c e was an a r g o n - i o n l a s e r o p e r a t i n p a t h = 5145 ' w i t h a power o f about 500 mW.
JOURNAL
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PHYSIQUEF i r s t , we present measurements o f Rayleigh s c a t t e r i n g i n t e n s i t y , f o r x = 0.1 w i t h the purpose o f i n v e s t i g a t i n g t e x t u r a l changes under thermal treatment around Tg (Fig.1). The s c a t t e r i n g i n t e n s i t y f o l l o w s a t n law, where t i s the time o f treatment and n an exponent n e a r l y equal t o 2
.
F i g . 1
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Rayleiah i n t e n s i t y versus time f o r h e a t treatment near Tg i n(Liu)~. 105 H200.845 '
The c l a s s i c a l theory o f Ray1 e i gh s c a t t e r i n g p r e d i c t s :
where N i s the number o f s c a t t e t b i n o p a r t i c l e s , v as t h e p a r t i c l e volume, B i s the s c a t t e r i n g angle, n i s t h e r e l a t i v e r e f r a c t i v e index o f p a r t i c l e t o s o l v e n t and A i s t h e l i g h t wavelenght. I f t h e process o f c r y s t a l growth f o l l o w s :
i n t h e Ostwald regime ( v o and t o are a r b i t r a r y i n i t i a l values), and assuming a constant p a r t i c l e number, one f i n d s
i n good agreement w i t h t h e experiments. On t h e b a s i s o f previous neutron s c a t t e r i n g r e s u l t s , t h i s observation can be r e l a t e d t o phase s e p a r a t i o n through i c e p r e c i p i - t a t i o n .
F i g . 3
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Temperature dependence o f t h e B r i l l o u i n frequency s h i f t f o r various concentrations. 5 I,
( L i C O x ( H ~ O ) I-x -i*
-pure water r - 0 ( r e f . ) A x 1 0.04+
x-
0 . 0 8 A1.
A r-
0 . 1 2\
'.
x - 0 . 1 6t
*..-.
*%./
.
.*-- -A- A-:-A~A-A- A ~ A/*
_*-*
*-*-I P-
*.*Ct*yt A/,~'A--
i o n s was proposed as a microscopic o r i a i n o f t h e r e l a x a t i o n ( 7 ) . For temperatures above 256 K, e l a s t i c waves are decoupled from t h i s r e l a x a t i o n . The unusual p o s i t i v e slope o f t h e v e l o c i t y vs temperature, which i s a known behaviour o f supercooled water (8), i s a l s o observed f o r x < 0.1
.
This e f f e c t , which does n o t seem t o have a r e l a x a t i o n a l o r i g i n , decreases w i t h i n c r e a s i n g LiCL content. This i s p o s s i b l y r e l a t e d t o the f a c t t h a t LiCL s o l u t e breaks hydrogen bonds.JOURNAL
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PHYSIQUEREFERENCES
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