X-RAYS DIFFRACTION STUDY OF BINARY METALLIC Cu-Y GLASSES USING ANOMALOUS DISPERSION

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X-RAYS DIFFRACTION STUDY OF BINARY

METALLIC Cu-Y GLASSES USING ANOMALOUS

DISPERSION

M. Laridjani, P. Leboucher, D. Raoux, J. Sadoc

To cite this version:

X-RAYS DIFFRACTION STUDY OF BINARY METALLIC Cu-Y GLASSES

USING ANOMALOUS DISPERSION

M. Laridjani, P. Leboucher, D. Raoux and J.F. ~adoc*

LURE, Bctirnent 209C, FacuZte' d e s S c i e n c e s , 92405 Orsay, France

* p h y s i q u e d e s SoZides, Betirnent 510, FacuZte' d e s S c i e n c e s , 91405 Orsay, France

Rdsumd

-

La m d t h o d e de d i f f r a c t i o n a n o m a l e d e s r a y o n s X a 6 t 6 utilisd pour d s t e r m i n e r l e s f o n c t i o n s d e d i s t r i b u t i o n r a d i a l e partielles pour un alliage amorphe Cu-Y.

Abstract

-

A n o m a l o u s X-ray d i f f r a c t i n method h a s b e e n used to obtained partial radial distribution f u n c t i o n s for a n a m o r p h o u s alloy Cu-Y.

The information a b o u t environment of e a c h c o m p o n e n t in a n a l l o y c a n be obtained from p a r t 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 t h e s p e c i f i c a t o m i c species. T h e p a r t i a l f u n c t i o n i s d e t e r m i n e d b y d i f f e r e n t t e c h n i q u e (1) o n e of these t e c h n i q u e s , w h i c h h a s b e e n d e v e l o p e d r e c e n t l y ( 2 , 3 ) , i s t h e X-ray d i f f r a c t i o n , i n w h i c h t h e anomalous dispersion effects. I n this t e c h n i q u e the partial r a d i a l distribution function can be obtained by using the variation of atomic scattering as the function of photon energy near the absorption edge. Generally, the total a t o m i c s c a t t e r i n g f a c t o r (f) is complex. The total atomic scattering can be written as :

f(k,w) = f, (k)

+

f' (K, w) i f" (k,w)

Here f, is the atomic scattering factor for radiation w i t h a frequency much higher than the absorption edge. It is only a s y n c h r o t r o n r a d i a t i o n s o u r c e that p r o v i d e s a p o w e r f u l f l u x o n the a d j u s t a b l e wavelengths either close or away from the absorption edge.

In this paper the results of our resonance X-Ray d i f f r a c t i o n study of sputter deposited amorphous Cu5Y and Cu2Y are discussed.

I n order to obtain the different total interference function which can be obtained by modifying the total scattering f a c t o r r a t i o , i n the case of a binary alloy, three experiments with three d i f f e r e n t wavelengths must be done.

The total interference function can be defined by : 2

c:~

lfCu(~)

+ AfCU(K,u)

1

C:

Ity(")

+ AfCu (K,u)I2

J (K,w) = y ~ u - ~ u + Y + A2 A2 Y-Y (K) + A L ~ ( K , W ~

ECu(~)

+ dfCu (K.~J" + C C + conj.}' Y ~ ( 1 ) ~ - ~ where Y Cu A~ Af(K,w) = f' (K,fi,)

+

i f" (K,w)

and

*2alCcu~Cu(K)

+ A£(K,U~ +

c,,

cy(~)

+ ~ f , ,

The three independant partial functions a r e defined i n the c o n v e n t i o n a l way ( 3 . ) . T h e b e s t i s t o o b t a i n J(K,w) f r o m t h r e e different energies : one far away from the absorpti-oh edges, one very

C8-158 JOURNAL DE PHYSIQUE

close to theyabsorption K-edge, and one very close to the Cu a b s o r p t i o n K-edge. But it is known that a good resolution on a P.D.R. f u n c t i o n n e e d s a s h o r t w a v e l e n g t h i n o r d e r to h a v e a l a r g e K v a l u e . A wavelength close to the Cu K-edge o n l y a l l o w s Kma, of the order of 9 1 - 1 which gives a weak resolution. I n the c a s e of C u 5 Y a l l o y it

was possible to by-pass this limitation. The low value of the Yttrium content l e a d s to a c o n t r i b u t i o n of Y p a r t i a l f u n c t i o n w h i c h is always very small. So it is possible zcyneglect this c o n t r i b u t i o n or to suppose a very simple Y function and to derive the o t h e r p a r t i a l functions. In this c a s e o n l y two e x p e r i m e n t s are n e e d e d both w i t h high energies.

THE EXPERIMENTAL PROCEDURE

The ductile a m o r p h o u s f o i l s of C u 5 Y was prepared by D.C. triod sputtering using Al. Substrate.

The experiment was carried out at a beam l i n e D l a t L U R E , which i s e q u i p p e d w i t h a channel-cut Si (220) s i n g l e c r y s t a l a s a monochromator with an energy resolution of 10 eV at 17000 eV. The DCI ring was operated at 1.72 and 1.85 GeV.

The diffraction intensity I(K) was measured at two e n e r g i e s b e l o w a n d o n the Cu and Y , K a b s o r p t i o n edges. I n o r d e r t o a v o i d fluorescence the scattered beam was recorded by an e n e r g y d i s p e r s i v e d e t e c t o r s , of l i t h i u m - d r i f t e d s i l i c o n , c o n n e c t e d w i t h a p u l s e processor. The detail of the experiment is described elsewhere (3)

RESULTS AND DISCUSSION

A s the energy r e s o l t u i o n of the solid s t a t e d e t e c t o r i s about 180 eV, for a photon energy near 8000 e V , it was s u f f i c i e n t to resolve the fluorescence lines Ka and KB of Y but not adequate e n o u g h to resolve K B from the elastically scattered photon.

The fluorescence line i n t e n s i t i e s a r e v e r y i m p o r t a n t w h e n the incident beam energy is over the absorption edge, but even when it is below the absorption edge the intensities s t i l l persist. This is due to Raman resonant e f f e c t , but a l s o to a s m a l l a m o u n t of second harmonic energy in the incident beam.

An accurate estimation of the K intensity is n e s c e s s a r y to be substracted from the diffracted intensity. We have supposed a ratio b e t w e e n the K and Ka i n t e n s i t i e s i n d e p e n d a n t o f t h e e x c i t a t i o n energy. A precfse measurement of the two f l u o r e s c e n t l i n e s w i t h an e x c i t a t i o n e n e r g y w e l l r e s o l v e d f r o m KB g i v e s 5 y/Kay = 0.235 a n d K-cu/KCu = 0.16

8 a The diffracted intensities were normalized with the incident beam or with the fluorescence intensity of Cu-Ka i n o r d e r to take i n account the time decrease of the beam.

According to the above c o r r e c t i o n s and n o r m a l s a t i o n s J(K) f u n c t i o n s a r e obtained w i t h a s a t i s f a c t o r y r e p r o d u c t i b i l i t y f o r different experiments performed at the same energy.

S o t h e v a r i a t i o n s i n t h e f e a t u r e s o f t h e t w o J ( K , w ) functions related to anomalous dispersion are significant.

In order to normalize the scattered intensity, the v a l u e of f' at E = 17036 eV w a s assumed f' = -6. T h i s was o b t a i n e d f r o m the theoretical value, c a l c u l a t e d i n the r e f e r e n c e ( 4 ) . T h e y h a v e used Cromer and Liberman relations.

Fig. (1) shows two reduced interference functions

features of amorphous metallic radial distribution f u n c t i o n w i t h two well resolved first i n t e r a t o m i c distances. At f i r s t sight it s e e m s reasonable to consider the first peak as the Cu-Cu first distance, and the second peak to Cu-Y.

THE PARTIAL INTERFERENCE AND DISTRIBUTION FUNCTION

For a diluted alloy such as Cu5Y a s it was mentioned a b o v e , the contribution of Y y - y is weak i n both c a s e s of energy. T h e r e f o r e t h i s f u n c t i o n c a n be t a k e n a s a n a j u s t a b l e p a r a m e t e r ; a n d by i n v e r s i o n , t h e l i n e a r s y s t e m c a n be s o l v e d w i t h t h e t w o u n k n o w n functions Y

cu-cU

and Y

-cu.

Fig. (3) shows the two partial i n t e r f e r e n c e f u n c t i o n s for the amorphous alloy Cu5Y evaluated from the i n d e p a n d e n t f u n c t i o n s as it was mentioned above.

But the information on the atomic distribution f u n c t i o n s in r e a l s p a c e is g i v e n by the Yourier transformation o f e a c h p a r t i a l interference function.

F i g .

(4)

s h o w s t h e t w o p a r t i a l r a d i a l d i s t r i b u t i o n functions w(R) of Cu-Cu and Cu-Y. T h e s e f u n c t i o n s permit u s to find distances occurring in Cu-Cu and Cu-Y pairs. The f i r s t peak of the Cu-Cu partial function corresponds to a d i s t a n c e at 2.50

A .

At the foot of this peak t h e r e is a n o t h e r d i s t a n c e at 3.32

A

w h i c h c a n be interpreted as a second site for Cu atoms. On the other f u n c t i o n , corresponding to Cu-Y d i s t a n c e s , the f i r s t peak is at 3.0

A .

The atomic radius of Cu is 1.28

A

and the atomic r a d i u s of Y is 1.78

8

: experimental distances are slightly contracted if we refer to a t o m i c radius. Other distances appear in Fig. 4 ; similar d i s t a n c e s i n the crystalline phase Cu Y are presented i n table 1. C o o r d i n a t i o n numbers obtained from these functions are given in table 2.

If we compare the present result with the first d i s t a n c e in the crystalline C U ~ Y , table (I), we find certain r e s e m b l a n c e s b e t w e e n t h e l o c a l o r d e r i n a m o r p h o u s a n d t h e c r y s t a l l i n e p h a s e . T h i s resemblance is shown by the EXAFS m e t h o d s also. T a b l e (2) shows the coordination numbers of the two phases in which we cannot observed the indicated similarity.

W e have c h e c k e d t h e s e r e s u l t s w i t h r a d i a l d i s t r i b u t i o n functions obtained from interference f u n c t i o n s m e a s u r e d w i t h photon energy close to the Cu absorption edge. F i r s t and second d i s t a n c e s agree with the Y e d g e results. C o o r d i n a t i o n n u m b e r s obtained f r o m Cu-Cu and Cu-Y function also agree. But there is no hope to determine The function by comparison of results obtained w i t h p h o t o n e n e r g i e s

corresponding to Y-edge and C u - e d g e , b e c a u s e d u e to the s m a l l K v a l u e ( K = 8 ) n o t h i n g c a n be c o n c l u e d o n d i s t a n c e s whp$% contribute lightly to interference functions.

For obtaining the Y y-ycontribution we change the composition of the alloy toCu2Y. As it is m e n t i o n e d . W e d i d t h r e e i n d e p e n d e n t experiments with three different energies near the absorption edge of Y. The analysis of the data is in progress.

Table 1

-

Interatomic first distances in the Crystalline Cu Y (5) and amorphous phase. 5

. .

:.

.

.

. .

: .

. .

. .

. .

i :

.

.

.

.

( CRYSTALINE PHASE : AMORPHOUS PHASE)

(Cu -Cu : Cu -Cu : Cu -Cu : Cu Y : Cu -Y : Cu-Cu : Cu Y )

(--IL---LL--,-5L---L-I----J----L---I-I-I-I-I---2J---:

) ( 2 - 4 9 AO: 2.51 fi : 2.88 f i : 2.88 f i : 3.23 fi : 2.50

A

: 3

A

) tribution function W cu-CU and W cu-y T a b l e 2

-

Atom t a k e n number o f Cu number o f Y T o t a l ( 2 ) mean c o o r d i - - a s o r i g i n a r o u n d i t a r o u n d i t n a t i o n number ( 2 )

___---_____________

...

---

a m o r p h o u s Cu 7 . 4 + 3

-

1 0 . 3 2 . 8 * 1 3 . 2 ( 0 . 5 )

...

13.75 Cu5Y Y 1 4 . 3 9 2 1 6 . 5 ( 0 . 5 )

_---

________--___

...

----

---

c r y s t a l l i n e Cu ( I o r X I ) 8 o r 9 ( 8 . 3 3 ) 4 o r 3 ( 3 . 6 6 ) 1 2 - - - , - - - 13.33 C u 5 Y Y 18 2 2 0

*

H y p o t h e t i c a l a s i n t h e c r y s t a l ( R 8 f . 1 8 ) .

2

4

6

8

10

REFERENCES

/1/ J.F. SADOC and C.W.J. WAGNER, Glassy Metals 11, Vol. 53 (1983) ed. Bzck and Guntherdt (Springer)

121

P. FUOSS

,

P . EISENBERGER, W. WARBURTON, A. BIENENSTOCK Phys. Rev. Let. 46 1957 (1981)

/3/ M. LARIDJAVI, J.F. SADOC and D. RAOUX Submitted to J.N.C.S. (1985)

/4/ SASAKI, KEK Report 83-22, National Lab. for High Energy Oho-machi, Tsukuba gun 1 barki-ken 305 Japon