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DETERMINATION OF THE LOCAL STRUCTURE OF METALLIC GLASSES BY EXAFS

A. Sadoc, A. Flank, D. Raoux, P. Lagarde

To cite this version:

A. Sadoc, A. Flank, D. Raoux, P. Lagarde. DETERMINATION OF THE LOCAL STRUCTURE OF METALLIC GLASSES BY EXAFS. Journal de Physique Colloques, 1982, 43 (C9), pp.C9-43-C9-46.

�10.1051/jphyscol:1982908�. �jpa-00222401�

JOURNAL DE PHYSIQUE

Colloque C9, supplément au n°12, Tome 43, décembre 1982 page C9-43

DETERMINATION OF THE LOCAL STRUCTURE OF METALLIC GLASSES BY EXAFS

A . Sadoc* A . M. F l a n k , D. Raoux * and P. L a g a r d e

LURB, Bât. 209C, Université Paris-Sud, 91405, Orsay Cedex, France

*Laboratoire de Physique des Solides, Bât. 510, Université Paris-Sud, 91405 Orsay Cedex, France

^Laboratoire de Métallurgie Physique, Université de Poitiers, 86000 Poitiers, France

Résumé. - La s t r u c t u r e l o c a l e des a l l i a g e s amorphes CU6Q ^/\.Q e t CU46 ^54 a été examinée par Exafs. De plus l ' e f f e t d'une r e l a x a t i o n s t r u c t u r a l e a été étudié dans CU45 I r ^ .

A b s t r a c t . - The l o c a l s t r u c t u r e o f CU50 ZV^Q and CU46 Zr54 amorphous a l l o y s has been i n v e s t i g a t e d by Exafs. Moreover the e f f e c t o f a s t r u c t u r a l r e l a - x a t i o n has been s t u d i e d i n Cu4g Z r ^ , .

I n t r o d u c t i o n . - In the past few y e a r s , the Exafs spectroscopy has been a p p l i e d to the determination o f the l o c a l s t r u c t u r e o f m e t a l l i c and m e t a l - m e t a l l o i d g l a s - s e s ( l - 6 ) . A c o n t r i b u t i o n o f Exafs i s t o have shown the asymmetry o f the r a d i a l d i s t r i b u t i o n f u n c t i o n o f some p a i r s o f atoms. The type of the asymmetrical f u n c - t i o n i s s t i l l a c o n t r o v e r s i a l p o i n t since i n some m e t a l l i c g l a s s e s , l i k e Niss Y33, CU50 Zr4Q, Cu-Y ( 3 , 4 , 6 ) , the Exafs spectra can only be reconstructed when using a t w o - s h e l l Gaussian model. I n m e t a l - m e t a l l o i d glasses l i k e C08O p2 0 (4) they can be f i t t e d as w e l l w i t h a d i s t r i b u t i o n decreasing e x p o n e n t i a l l y w i t h the d i s t a n c e ( 5 ) . We have also found some s i m i l a r i t i e s between the l o c a l s t r u c t u r e s o f the amorphous compound Cu6o Zr40 and the c r y s t a l l i n e one Cuig Zrj ( 6 ) . We w i l l i n v e s t i g a t e here an other Cu-Zr a l l o y , the CU45 Zr54 one. Haensel e t a l . ( 5 ) have y e t analysed the Exafs o f such an a l l o y on the Zr edge but have not determined the Cu environment.

Exafs being a microscopic probe could provide unique i n f o r m a t i o n on the process o f c r y s t a l l i s a t i o n and i n p a r t i c u l a r f o r heat treatment near Tg when the s o - c a l l e d s t r u c t u r a l r e l a x a t i o n takes p l a c e . We have found l i t t l e evidence o f s t r u c t u r a l rearrangement f o r Cu-Ti and Cu-Y annealed samples. A new attempt has been made i n CU46 Zr54 f o r which several experiments ( s u p e r c o n d u c t i v i t y ( 7 ) and d i f f e r e n t i a l scan- ning c a l o r i m e t r y - M. Harmelin, Y. Calvayrac, A.M. Quivy, C.E.C.f"., V i t r y , France) have l e d t o the conclusion t h a t the l o c a l s t r u c t u r e could be m o d i f i e d . We r e p o r t also here our r e s u l t s f o r CU45 Zr54 a f t e r heat treatment near Tg.

Experimental

The amorphous a l l o y s were prepared by quenching from the m e l t , r o l l e r - q u e n c h i n g technique f o r CU6Q Z ^ Q , m e l t - s p i n n i n g method f o r Cu4g Zr54. C r y s t a l l i n e samples, CU45 Zr54, Cu Zrg and pure Z r , were s t u d i e d too f o r comparison. The amorphous and c r y s t a l l i n e a l l o y s as w e l l as the annealed CU45 Z r ^ one were k i n d l y s u p p l i e d by Y. Calvayrac and A.M. Quivy. They have also v e r i f i e d the amorphous s t a t e o f the glassy samples by X-ray d i f f r a c t i o n .

The Exafs spectra were recorded a t 30 K using D C I storage r i n g (LURE, Orsay, France).

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982908

JOURNAL DE PHYSIQUE

Crystalline s t r u c t u r e s

Cu Zr7 i s isostructural t o Nil0 Zr7 where the Ni-Ni f i r s t distances range from 2.19

8

t o 3.08

8.

A t the opposite,

Cu

Zrz which c r y s t a l l i z e s in a tetragonal s t r u c - ture has no Cu-Cu nearest neighbour. There a r e a l s o no Cu-Cu nearest pair of atoms in Cu

Zr

a t high temperature (Cs C1 s t r u c t u r e ) .

B u t

t h i s phase i s unstable a t room temperature. Then

Cu

Zr, l i k e c r y s t a l l i z e d Cu46 Zr54. i s a mixture of C u l o Zr7 and Cu Zr2 phases.

The lack of Cu atoms in the f i r s t coordination shell of

C u i n

Cu Zr2 i s well obser- ved by Exafs.

On

Cu edge the Fourier transform of the spectrum exhibits no peak a t

% 2.2

fi

(uncorrected f o r phase s h i f t ) where i t happens t o be f o r Cu

- C u

next nea- r e s t neighbour pairs. For c r y s t a l l i z e d Cu45 Zr54 there i s a small peak a t 2.2 fi due t o the C u l o Zr7 phase. l i o r e o ~ e r , on the Zr edge, i t must be pointed out t h a t no main peak appears i n the 3.4 region of the F.T. f o r any C U

Zr54, C u

~ ~ Zr2 and pure

Zr

spectra. This will be a crucial point i n t h e following.

Amorphous a1 loys As -quenched sanpl es

On the Cu edge, the spectrum of Cu46 ZrS4 i s similar t o the Cu60 Zrqo one in the high energy region where they a r e dominated by the nearest Cu neighbours a t about 2.52

a,

t h e i r d i s t r i b u t i o n being thus similar

i n

both amorphous a l l o y s . This i s a l s o i l l u s t r a t e d by looking a t the F.T of the spectra (Fig.la,b) which exhibit a large peak a t ^Q, 2.2

a

contrary t o c r y s t a l l i z e d Cu46 Zr54 and Cu Zr2. The f a c t t h a t the local s t r u c t u r e around

Cu

i s the same f o r both alloys implies the existence of a chemical order. A similar r e s u l t was found

i n

Cu-Ti alloys where the spectra on

C u

edge were a l i k e f o r a wide range of concentration ( 4 ) . For E < 300 eV, the spectrum i s however somewhat weaker f o r Cu46

Zr

4 than f o r C U Zr40. ~ ~ This can be interpreted by the f a c t t h a t the contribution o? the 2nd

Cu-Cu

shell found in

CubO

ZrqO i s not here completely out of phase with the contribution from Zr neighbours.

As f o r Zr edge, the F.T. of Cu46 Zr54 spectrum exhibits a we1 1-defined 2nd peak a t

"J 2.9

1

due mainly t o Zr-Zr pairs. This peak i s reduced t o a small bump

i n

Cu60

Zr40

(Fiy.Za,b); t h i s has been interpreted i n ( 6 ) by the contribution of a 2nd Z r - C u sabshell. So t h i s Zr-Cu subshell must be l e s s important in Cu45 Zr54 and the

Zr-Cu

d i s t r i b u t i o n l e s s asymmetrical.

The inverse F.T. (Fig.3,4a) a r e well f i t t e d when using the coordination numbers N , distances R and disorder parameters o of Table I . Iloreover, our r e s u l t s compare well with those obtained on

Zr

edge by Haensel e t a1.(5) in a Cu46 Zr54 alloy.

Their Exafs spectrum was analyzed using an exponential d i s t r i b u t i o n f o r the hetero- gen pairs. The

Z r - C u

d i s t r i b u t i o n i s not very much asymmetrical. So the same type of R.D.F. can be obtained with the two models, an exponentially decreasing d i s t r i b u - tion of distances and a two-shell model. This i s not the case f o r Cub0 Zr40 where we had evidence of a two-shell distribution of distances ( 6 ) .

Relaxed Cua6 ZrS4

Strong modifications appear i n the Exafs spectra of C U Zr54 a f t e r relaxation. ~ ~ On Zr edge, the F.T. consistsnow of three peaks. The amplitude of the 2nd one, due mainly t o Zr-Zr pairs, has doubled.

B u t

the most remarkable e f f e c t i s the presence of a t h i r d peak a t 3.4

a

(uncorrected f o r phase s h i f t ) which does not e x i s t i n Cu-Zr crystal l i n e phases. This peak can be interpreted by Zr-Zr pairs a t 3.77

8

or by a mixing of these Zr-Zr pairs w i t h Zr-Cu ones a t 'l. 3.90

A .

Such a Cu-Zr distance does not f a l l i n the central peak of the

F.T.

on

Cu

edge so t h a t i t s existence can be ruled out.

Good simulation of the spectra can be obtained with the parameters of Table

I

I

^I I I I ^{1 I}

0 200 LOO

E (eV)

600' Fig.l:Cu edge. F.T. f o r (a)Cub0 Zr4 Fig.3:Cu edge. I n v e r s e F.T.(dots)and c a l c u - ( b ) u n t r e a t e d C q 6 Zr54 (c)anneale! l a t e d s p e c t r a ( s o l i d l i n e ) u s i n g p a r a m e t e r s Cu46 Zr54. o f Table I f o r Cu46 Z q 4 ( a ) b e f o r e and

( b ) a f t e r a n n e a l i n g .

L ^{I I I}

0 200 LOO

E (eV)

600

*

Fig.2:Same a s F i g . 1 on Z r edge. Fig.4: Same a s F i g . 3 on Zr edge

09-46 JOURNAL DE PHYSIQUE

(Fig.3,4b). The d i s o r d e r parameters decrease f o r a11 p a i r s i n p a r t i c u l a r f o r the Zr-Zr ones. An e x p l a n a t i o n o f i t s h i g h value before r e l a x a t i o n c o u l d be t h a t a 2nd Zr-Zr s h e l l s t i l l e x i s t s i n t h e u n t r e a t e d sample ( t h e r e i s a small wing i n t h e 2nd peak o f the F.T., f i g . Z b ) , b u t i s very disordered ( o > .16

a)

so t h a t o n l y the s h o r t e s t Zr-Zr d i s t a n c e can be obtained by Exafs.

The f a c t t h a t t h e number o f nearest Cu-Cu a t 2.53

1

does n o t decrease w i t h the r e l a - x a t i o n shows t h a t the l o c a l s t r u c t u r e does n o t change towards the c r y s t a l l i n e one, where t h e r e i s no Cu-Cu neighbours a t t h i s distance. Nevertheless, the 3 r d peak i n the F.T. on Z r edge gives t h e i n f o r m a t i o n o f an increase o f t h e l o c a l order around the Z r atom.

Acknovrledgements.

-

I t h a ~Lercnune ;to .thank Y. Cdvuy.rrac and A.M. QcLivy do4 pk~pahing t h e ~ampLe2 and dok en&gkten*ng dbcubbionb.

5 3.14 .14 5

- -

> . I 6 4.5 3.77

Table I.

-

E v o l u t i o n o f the s t r u c t u r a l parameters o f Cu, Zrl,, w i t h t h e concentra- t i o n and w i t h t h e thermal h e a t i n g (AN = k.5, Ao =

.011,

AR =r.018 f o r the f i r s t Cu-Cu subshell, AR 31.021 f o r the f i r s t Zr-Cu one and AR 32.051 f o r t h e o t h e r ones).

References

1

-

HAYES T.El., ALLEN J . U . , TAUC J., GIESSEN B.C., HAUSER J . J . , Phys.Rev.Lett.

2,

1282 (1978).

2

-

RAOUX D., SADOC J.F., LAGARDE P., SADOC A., FONTAINE A., J. de Physique

g,

207 (1980).

3

-

RAOUX D., SADOC A., LAGARDE P., FONTAINE A., Proc. o f the Daresbury Study lu'eek end "Exafs f o r I n o r g a n i c systems" compiled by GARNER C.D. and HASNAIN S.S., p.124 (1981).

4

-

FLANK A.N., LAGARDE P., RAOUX D., RIVORY J., SADOC A., 4 t h I n t e r n . Conf. on r a p i d l y quenched metals, Sendai (1981), v o l .I, p.393.

5

-

HAENSEL R., RABE P . , TOLKIEHN G., WERNER A., Proc. NATO Adv. Study I n s t . " L i q u i d and Amorphous metals" ed. by LUSCHER E.

,

REIDEL D., Dodrecht, p .467 (1981).

6

-

SADOC A., RAOUX D., LAGARDE

P . ,

FONTAINE A., J. o f Non C r y s t . S o l . ( t o be pub1 i shed).

7

-

GAROCHE P . , These d ' E t a t , Orsay, France (1981).

Cu60 Zr40 Cu46 Zr54 annealed

Cu-Cu

N

~ ( 1 )

.(a)

^{N R(W) ,(a)}

3.5 2.54 -10 3.5 2.53 .09

2.5 2.95

\

^{1 2.95}

"j