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:

M. Laridjani, P. Leboucher, D. Raoux, J. Sadoc. X-RAYS DIFFRACTION STUDY OF BINARY

METALLIC Cu-Y GLASSES USING ANOMALOUS DISPERSION. Journal de Physique Colloques,

1985, 46 (C8), pp.C8-157-C8-161. �10.1051/jphyscol:1985821�. �jpa-00225164�

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 :

c:~ lfCu(~)

^{+ AfCU(K,u)}

1

2 ^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

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985821

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

F(K) = K (J(K)-1) which have been derived from two energy measurements : E = 17036 e V (near t h e a b s o r p t i o n e d g e of Y) and E = 1 5 8 0 0 e V (below the absorption edge).

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.

Therefore, we believe that the important result of this work is to show useful aspects of anomalous dispersion effects for solving the structure problem in the disordered material.

C8-160 JOURNAL DE PHYSIQUE

- Cu-Cu

. . . . . . . c u -Y

f..

2

6

8 10

F i g ( 1 ) I n t e r f e - r e n c e f u n c t i o n s f o r t h e a m o r - p h o u s a l l o y C u 5 Y .

a

-

n e a r t h e y t t r i u m k

-

e d g e b

-

B e l o w t h e y t t r i u m K - e d g e

Fig. (2) T h e r e d u c e d 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 s d e r i v e d b y F o u r i e r t r a n s - f o r m f r o m

~ i ~ . l ( a ) a n d ( b )

F i g . (3) T h e p a r t i a l i n t e r - f e r e n c e f u n c - t i o n s Y

Cu-Cu a n d YCU-y d e r i v e d f r o m J (K)

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

/ 5 / J.H. WERNICK and S. GELLER Acta Cryst.

11,

^{662 (1959)}