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ELECTRONIC PROPERTIES OF AMORPHOUS
Cu60Zr40 ALLOY
P. Garoche, Y. Calvayrac, J. Veyssié
To cite this version:
JOURNAL DE PHYSIQUE CoZZoque C8, suppzdment au n08, M e 41, a o c t 1980, page
C8-766
ELECTRONIC PROPERTIES OF AMORPHOUS CuGOZr4,, ALLOY
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P. Garoche, Y. Calvayrac and J.J. veyssid**
Laboratoire de physique des s o l i d e s , U n i v e r s i t i Paris-Sud, 91405 Orsay, France.
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C. E. C.M., CNRS, 1 5 , r u e George Urbain, 94400 Vi'itry, France.**c.N.A.M. 292 r u e S t . Martin, 75141 Paris Ce'dem 03, France. A l t h o u g h a m o r p h o u s m e t a l s a n d m e t a l l i c glasses h a v e d r a w n much a t t e n t i o n i n t h e l a s t f e w y e a r s , t h e r e a r e s t i l l a n u m b e r o f u n r e s o l v e d p r o b l e m s c o n c e r n i n g t h e i r e l e c t r o n i c s t r u c t u r e a n d r e l a t e d p h y s i - c a l p r o p e r t i e s s u c h as s u p e r c o n d u c t i v i t y , m a g n e t i s m , c o h e s i v e e n e r g y a n d s t a b i l i t y . I n a d d i t i o n t o t h e t h e o r e t i c a l d i f f i c u l - t i e s i n h e r e n t t o b o t h t h e l o n g - r a n g e a n d s h o r t - r a n g e d i s o r d e r i n t h e s t r u c t u r e o f t h e s e m a t e r i a l s (1) t h e r e i s c l e a r l y t o o a l a c k o f e x p e r i m e n t a l d a t a r e g a r d i n g s o - me o f t h e m o r e s i g n i f i c a n t p a r a m e t e r s i n - v o l v e d . I n p a r t i c u l a r l o w t e m y e r a t u r e s p e c i f i c h e a t r e s u l t s a r e v e r y s c a r c e . The m a i n r e a s o n i s t h a t v e r y f e w s y s t e m s may b e p r e p a r e d i n a m o r p h o u s b u l k s t a t e a n d t h e s m a l l s a m p l e q u a n t i t i e s g e n e r a l l y a - v a i l a b l e make a c c u r a t e d a t a d i f f i c u l t t o o b t a i n . T h e r e f o r e we h a v e c o n s i d e r e d o f i n t e r e s t t o u n d e r t a k e a s t u d y o f t h e a - mor~hous a l l o y s s e r i e s Zrx Cul-,. Here we present r e s u l t s f o r x = .4 F i r s t , t h e a m o r b h o u s s t a t e i s s t a b l e a t r o o m t e m p e r a t u r e o v e r a r a t h e r w i d e com- p o s i t i o n a l r a n g e , g i v i n g t h e o p p o r t u n i t y t o i n v e s t i g a t e t h e t r e n d s o f t h e d e n s i t y o f s t a t e s a t t h e F e r m i l e v e l as a f u n c t i - on o f c o m p o s i t i o n . I n t h i s r e s p e c t r e c e n t s t u d i e s b y p h o t o e m i s s i o n s p e c t r o s c o p y h a - v e r e v e a l e d a d - b a n d s t r u c t u r e w h i c h i s q u i t e c o n t r a s t e d w i t h t h a t o f o t h e r d - b a n d s y s t e m s ( 2 , 3 ) . w S e c o n d , Z r 7 4 Cu2$ h a s b e e n r e p o r t e d t o u n d e r g o a s u p e r c o n d u c t i n g t r a n s i t i o n n e a r 3 K (11) so t h a t a study o f t h e s y s t e m a t i c s o f s u p e r c o n d u c t i v i t y i n t h i s a l l o y s e r i e s i s e x p e c t e d t o p r o v i d e a d e e p e r i n s i g h t i n t o t h e e l e c t r o n i c p a r a m e t e r s i n v o l v e d . T. R i z o g u c h i e t a l l ( 4 ) h a v e r e p o r t e d s p e c i f i c h e a t d a t a on CuS7 Z r 4 3 a m o r p h o u s a n d c r y s t a l l i s e d a l l o y s b u t a c c o r d i n g t o t h i s a u - t h o r s t h e i r c r y s t a l l i s e d a l l o y s h o u l d b e a m i x t u r e o f Cu3 Z r 2 a n d Cu Z r . As a p a r t o f a c o n t i n u i n g s t u d y o f t h e s t r u c t u r a l , t h e r - mal a n d s u p e r c o n d u c t i n g p r o p e r t i e s o f t h i s a l l o y s e r i e s we p r e s e n t , i n t h i s p a p e r , r e - s u l t s o f s 2 e c i f i c h e a t m e a s u r e m e n t s on t h e a l l o y Z r 4 0 C U f o r b o t h t h e a m o r p h o u s a n d ~ ~ c r y s t a l 1 i n e f o r m s . The s t a r t i n g a l l o y h a s b e e n p r e p a r e d f r o m e l e c t r o t y t i c c o p p e r a n d K r o l l z i r c o - n i u m b y l e v i t a t i o n m e l t i n g i n o r d e r t o p r e v e n t a n y c o n t a m i n a t i o n f r o m a c r u c i b l e . T h e i n g o t h a s b e e n s u b s e q u e n t l y b r o k e n i n t o s m a l l f r a g m e n t s a n d t h e a m o r p h o u s t h i n f o -
i l s have been obtained d i r e c t l y from l e v i t a t i o n by t h e t w i n - r o l l quenching technique. We obtained quenched samples i n form o f a r i b b o n w i t h a t y p i c a l t h i c k n e s s o f 1 0 0 p m a n d an a r e a o f s e v e r a l
2 cm
.
Fig
1-The diffracted
X
ray intensity Iexp
V . S .the diffraction angle 2
8 ,for
amor- p h o u s Cu 6 0 ZrQo a l l o y .The
beam divergen-ce
f o rcurve
1 was 0,25Oand that
f o rcur-
ve
2 was lo. A l l t h e s a m p l e s u s e d h a v e b e e n i n s p e c t e dfor
c r y s t a l l i n i t y b y X - r a y d i f f r a c t i o n u s i n g Co K ~ r a d i a t i o n . A t i m e l a p s e s t e p s c a n n i n g d i f f r a c t o m e t e r was a l s o u s e d t o o b t a i n a m o r e d e t a i l e d X - r a y s c a n w i t h a ni m p r o v e d s t a t i s t i c s ( f i g u r e 1 ) . The a b s e n c e o f a n y o x i d e p h a s e h a s b e e n c a r e f u l l y c h e c - k e d s i n c e t h e h i g h r e a c t i v i t y o f t h e s u r f a - c e t o o x y g e n , w i t h p o s s i b l e s u b s e q u e n t - t o n - t a m i n a t i o n o f t h e s a m p l e , may b e a t t h e o - r i g i n o f s e v e r e d r a w b a c k s w i t h t h i s s y s t e m . The t h e r m a l b e h a v i o u r o f t h e a- m o r p h o u s s t a t e o f t h e same s a m p l e was s t u - d i e d b y d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y u p t o 1.000K, w i t h a c o n t i n u o u s h e a t i n g r a - t e o f 10K/ m i n u t e ( 5 ) . The t h e r m o g r a m s e x - h i b i t e d a w e l l d e f i n e d g l a s s t r a n s i t i o n a t T
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700K a n d a s h a r p c r y s t a l l i z a t i o n p e a k 9 a t T c = 745K. No e x t r a p e a k was o b s e r v e d a - b o v e Tc, i n d i c a t i n g t h a t a s i n g l e c r y s t a l l i n e p h a s e i s f o r m e d a n d c o n f i r m i n g t h e a b s e n c e o f c o n t a m i n a t i o n b y o x y g e n . The c r y s t a l l i n e a l l o y u s e d i n t h e p r e s e n t i n v e s t i g a t i o n was o b t a i n e d b y a n n e a l i n g an i n i t i a l l y a m o r p h o u s s a m p l e a t 4 5 0 ° c f o r 4 8 h o u r s i n u l t r a h i g h vacuum,P=l o m 7
T o r r . The a n n e a l i n g a l l o y was i n s p e c - t e d b y X - r a y d i f f r a c t i o n a n d t h e r e s u l t i n g s p e c t r a was c o n s i s t e n t w i t h t h e s t r u c t u r e o f t h e compound Cu3 Z r 2 ( 6 ) . E l e c t r i c a l r e s i s t i v i t y m e a s u r e - m e n t s w e r e p e r f o r m e d down t o 0 . 3 K b y a c o n - v e n t i o n a l f o u r - p r o b e m e t h o d . No s u p e r c o ' n d u c t i n g t r a n s i t i o n was o b s e r v e d e i t h e r i n t h e a m o r p h o u s o r i n t h e c r y s t a l l i n e s a m p l e s . The h e a t c a p a c i t y m e a s u r e m e n t s w e r e made i n a 3 ~ e c r y o s t a t f r o m 0 . 3 K t o 10K b y u s i n g t h e a . c . c a l o r i m e t r y t e c h n i q u e p r e v i o u s l y d e s c r i b e d ( 7 ) . P r e l i m i n a r y c h e c k : w e r e p e r f o r m e d b e f o r e e a c h r u n , t o e n s u r e t h a t t h e d i f f u s i o n o f h e a t t h r o u g h t h e sam- p l e a s s e m b l y was a d e q u a t e . T y p i c a l l y t h e w o r k i n g f r e q u e n c y was 0.5Hz.
The h e a t c a - p a c i t y o f t h e s u b s t r a t e a n d a d d e n d a was measured separately. The sample masses were 15 and 18 mg f o r t h e amorphous and c r y s t a l l i n e states, ; r e s p e c t i v e l y . "hey c o n t r i b u t e d r o u g h l y ' f o r 80 % a t 0.3 K and 40 % a t 10 K t o , t h e whole heat c a p a c i t y .
(3-768
JOURNAL DE PHYSIQUE f* ~ R o ~ l d be n o t e d t h a t t h e c r y s t a l l i n e m a l y i n t h e s p e c i f i c h e a t o f t h e c r y s t a l l i s a m p l e e x h i b i t s an a n o m a l y b e l o w 1 . 3 K , ( f i g ne s a m p l e h a s n o t b e e n e l u c i d a t e d . 2 ) , t h e n a t u r e o f w h i c h h a s r e m a i n e d t i l l now u n e x p l a i n e d . T h e e x p e r i m e n t a l v a l u e s a r e :8
( a m o r p h o u s ) = 2 . 8 0f
4 i n J i m o l e K * a n d+
2 ( c r y s t a l ) = 2 . 6 4 - 4 m J / m o l e K when t h e a f o r e m e n t i o n n e d a n o m a l y i n t h e c r y s t a l l i - ne s t a t e i s i g n o r e d . The c o r r e s p o n d i n g va l u e s o f t h e d e n s i t y o f s t a t e s a t t h e F e r m i l e v e l a r e r e s p e c t i v e l y N ( E F ) a m o r p h o u s = 0,59f 0 , 0 1 s t a t e s ( e V , a t o m , d i r e c t i o n o f s p i n ) - ' a n d N ( E F ) c r y s t a l = 0,56f 0 , O l . T h e s e d e n s i t i e s o f s t a t e s a r e h i g h , t h e y a r e o f t h e same o r d e r o f m a g n i t u d e b u t s l i g h t l y r e d u c e d as c o m p a r e d t o p u r e c r y s t a l - l i n e Z r . T h i s o b s e r v a t i o n a g r e e s w i t h t h e r e s u l t s o f p h o t o e m i s s i o n s p e c t r o s c o p y mea- s u r e m e n t s ( 2 , 3 ) . F4oreover s p e c i f i c h e a t d a t a ( t o b e p u b l i s h e d l a t e r ) o n a m o r p h o u s s a m p l e s o f d i f f e r e n t c o n c e n t r a t i o n show t h a t N ( E F ) i n c r e a s e s w i t h i n c r e a s i n g Z r c o n t e n t . The same t r e n d h a s b e e n o b s e r v e d i n t h e p h o t o e m i s s i o n e x p e r i m e n t s o f r e f e - r e n c e 3 . 3 u t o u r r e s u l t s i n d i c a t e t h a t , f o r t h e h i g h e s t v a l u e s o f x, N ( E F ) i n t h e amor p h o u s Z r x Cul-, s y s t e m d o e x c e e d t h e c o r - r e s p o n d i n g v a l u e i n p u r e Z r . I t s h o u l d b e o u t 1 i n e d h o w e v e r t h a t t h i s f i n d i n g s c o n - c e r n s t h e e l e c t r o n - p h o n o n d r e s s e d d e n s i t y o f s t a t e s . The d e v i a t i o n s f r o m s t r a i g h t - l i n e b e h a v i o u r i n t h e p l o t o f C/T v s T~ n a y b e i m p u t e d t o t h e t e m p e r a t u r e d e p e n d e n c e o f t h e D e b y e t e m p e r a t u r eeD.
The e f f e c t i v e e D ( ~ ) h a s b e e n o b t a i n e d b y u s e o f t h e f u l l Debye m o d e l a n d p l o t t e d i n f i g u r e 4, w h e r e t h e e r r o r s b a r s r e p r e s e n t t h e e f f e c t o f a n u n c e r t a i n t y o ff
1% i n t h e w h o l e c a p a c i t y . I t a p p e a r s , f i r s t , t h a teD
i s n o t s t r o n g l y t e m p e r a t u r e d e p e n d e n t and, s e c o n d , t h a t i s r o u g h l y u n c h a n g e d i n t h e c r y s t a l l i n e s t a t e as c o m p a r e d t o t h e a m o r p h o u s s t a t e . T h i s l a s t r e s u l t i s a t v a r i a n c e w i t h p r e v i o u s s t u d i e s o f t h e Pd S i s y s t e m ( 9 ) w h e r e a s t r i k i n g s o f t e n i n g o f l o n g w a v e l e n g t h t r a n s v e r s e a c o u s t i c p h o n o n s h a s b e e n o b s e r v e d i n t h e g l a s s r e l a t i v e t o t h e c r y s t - a l . H o w e v e r t h i s p o i n t m u s t b e c o n s i d e r e d w i t h c a u t i o n a s l o n g a s t h e o r i g i n o f t h e a n o -A M O R P H E
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The e f f e c t i v e Debye t e m p e r a t u r e e D i n amor phous and c r y s t a l l i n e Cu60 Z r 4 0 v e r s u s a b -
R e f e r e n c e s ( 1 ) Khanna S.N. a n d C y r o t - L a c k m a n n F.,Phys Rev B 2 1 ( 1 9 8 0 ) , 1 4 1 2 . ( 2 ) A m G o u A. a n d K r i l l G . , S o l i d S t a t e Comm. 2 8 ( 1 9 7 8 ) , 9 5 7 . 1 3 1 OeTFiafen P.. H a n s e r E . , G U n t h e r a d t H . J . a n d Bennemann K ~ H . , P h y s . Rev L e t t . % , 1 1 9 7 9 ) . 1 1 3 4 . ( 4 ) ~ l i i z o ~ u c h i , S . v o n l l o l n a r , a n d G.S. C a r g i l l 1 1 1 , T K u d o , P r o c e d i n g o f t h e s e - c o n d I n t . C o n f . o n a m o r p h o u s m a g n e t i s m , E - d i t e d b y R.A. L e v y a n d R. Hasegawa, ( 1 9 7 7 ) P l e n u m P r e s s
