DIFFERENCE IN Fe ATOM ENVIRONMENTS BETWEEN CuFe (2% Fe) AND CuAuFe (1 AND 3% Fe) ALLOYS

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DIFFERENCE IN Fe ATOM ENVIRONMENTS BETWEEN CuFe (2% Fe) AND CuAuFe (1 AND 3%

Fe) ALLOYS

J. Budnick, M. Choi, G. Hayes, D. Pease, Z. Tan, E. Klein, B. Illerhaus

To cite this version:

J. Budnick, M. Choi, G. Hayes, D. Pease, Z. Tan, et al.. DIFFERENCE IN Fe ATOM ENVIRON-

MENTS BETWEEN CuFe (2% Fe) AND CuAuFe (1 AND 3% Fe) ALLOYS. Journal de Physique

Colloques, 1986, 47 (C8), pp.C8-1037-C8-1040. �10.1051/jphyscol:19868200�. �jpa-00226108�

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DIFFERENCE

I N Fe

ATOM ENVIRONMENTS BETWEEN C u F e ( 2 % F e ) AND CuAuFe (1 AND 3% F e ) ALLOYS

J. I. B U D N I C K , M. H. CHOI, G.H. HAYES(

)

, D.M. PEASE,

2 .

T A N , E. **KLEIN* and B. ILLERHAUS"**

Department of Physics and Institute of Materials Science, University of Comecticut, Storrs, CT 06268, U. S.A.

' ~ n s t i t u t fiir Atom und Festerkorper Physik, Freie Universitat Berlin, 0-1000 Berlin 33, F.R.G.

Abstract.-- According t o r e c e n t 5 7 ~ e - ~ b ; s s b a u e r measurements made a t 4.2K, Fe atoms i n Cu Au Fe, and Cu Au Fe a r e dominantly 0 8 0 % ) f e r r o m a g n e t i c . whereas Fe n ? m a O i n ~ u ~ ~ ~ e ~ ~ Z a n $ R s Z a n t i f e r r m a g n e t i c i n t e r a c t i o n s ( < I N f e r r o m a g n e t i c ) . The Fe K-edge XANES and EXAFS measurements have been made on t h e s e a l l o y s . F l u o r e s c e n c e , as w e l l a s t r a n s m i s s i o n , d a t a have been

o b t a i n e d . The XANES and

EXAFS

s p e c t r a f o r t h e CuAuFe a l l o y s a r e q u i t e s i m i - l a r t o t h e s p e c t r a f o r d - F e , which seems t o r e f l e c t t h e c l u s t e r i n g o f f e r r o - magnetic bcc Fe. On t h e o t h e r hand, t h e XANES and EXAFS f o r Cu Fe c l o s e l y resemble t h o s e o f f c c N i r s t r o n g l y i n d i c a t i n g t h e environment 088an2iferro- magnetic f c c r - ~ e . Moreover, t h e F o u r i e r t r a n s f o r m f o r Cu Fe shows more smeared o u t h i g h e r s h e l l peaks compared w i t h t h o s e f o r

CUAU~!.

2 ~ h i s may be t h e r e s u l t of v a r y i n g s i z e s of Fe c l u s t e r s .

I n t r o d u c t i o n

The e q u i l i b r i u m s o l u b i l i t y o f Fe i n Cu which i s 3 at.

$

a t 1 0 6 0 ~ ~ d r o p s s h a r p l y w i t h d e c r e a s i n g t e m p e r a t u r e and is o n l y 0.5 a t . I a t 6 0 0 ' ~ ( I ) .

A

s u p e r s a t u r a t e d c o p p e r - r i c h Cu-Fe s o l i d s o l u t i o n o b t a i n e d by quenching from a high t e m p e r a t u r e t h u s h a s provided a most i n t e r e s t i n g system f o r s t u d y i n g t h e environment of d i l u t e con- c e n t r a t i o n F e atoms. B i t t e r and Kaufmann ( 2 ) o r i g i n a l l y s u g g e s t e d t h a t , i n s u c h a copper-rich Cu-Fe s o l i d s o l u t i o n , Fe atoms i n i t i a l l y p r e c i p i t a t e a s p a r t i c l e s o f f a c e - c e n t e r e d c u b i c ( f c c ) g - ~ e c o h e r e n t w i t h t h e Cu m a t r i x , and t h a t t h e r - F e phase t r a n s f o r m s t o t h e i n c o h e r e n t body-centered c u b i c ( b c c ) d - ~ e phase d u r i n g c o l d r o l l i n g o r l o n g a g i n g . T h i s mechanism of c o h e r e n t ) f - ~ e p r e c i p i t a t i o n was confirmed i n t h e c a s e o f Cu by Newkirk ( 3 ) w i t h t h e X-ray d i f f r a c t i o n and o t h e r t e c h n i q u e s . The r - F ~ $ : & i ? t a t e s , u n l e s s c o l d - r o l l e d , t r a n s f o r m t o +-Fe a t and below room t e m p e r a t u r e only o v e r a n extended p e r i o d o f t i m e . Hence, Abrahams e t

al.

( 4 ) c a r r i e d o u t n e u t r o n d i f f r a c t i o n measurements o n t h e p r e c i p i - t a t e s i n Cu-Fe a l l o y s w i t h 2.8 and 3.3 a t . % Fe t o i n v e s t i g a t e t h e magnetic s t r u c - t u r e o f r - F e . and determined t h a t t h e r - F e p a r t i c l e s a r e a n t i f e r r m a g n e t i c . How- e v e r , a c c o r d i n g t o a Mossbauer study o f Cu Fe by Window ( 5 ) * t h e p r e c i p i t a t e s c o n s i s t of v a r y i n g s i z e s o f Fe c l u s t e r s wi?# different numbers o f Fe n e a r neigh- bors, and o n l y l a r g e c l u s t e r s behave a s r - F e .

On t h e o t h e r hand. i n 1980, Gonser e t

al.

( 6 ) r e p o r t e d t h a t f e r r o m a g n e t i c f c c r - F e p r e c i p i t a t e s w e r e found i n a Cu Au F e a l l o y . They i n t e r p r e t e d t h e f i n d i n g i n t e r m s o f t h e change i n t h e l a t t i c e 6 g o n z ? a n l by p o s t u l a t i n g t h a t , when t h e l a t - t i c e parameter of t h e Cu h o s t i n c r e a s e s w i t h an a d d i t i o n of Au. t h e i n c r e a s e i n t h e

("present Address : Optical Group Research.

Perkin-Elmer Corporation,

Danbury. CT 06810, U.S.A.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19868200

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C8-1038 JOURNAL DE PHYSIQUE

a t a n i c d i s t a n c e changes t h e s i g n o f t h e exchange i n t e r a c t i o n t h u s c a u s i n g a t r a n - s i t i o n from a n t i f e r r o m a g n e t i c t o f e r r o m a g n e t i c r - F e . T h i s f i n d i n g was l a t e r cor- r e c t e d

by

Schneeweiss e t a l . ( 7 ) based-on t h e d i s c o v e r y t h a t t h e p r e c i p i t a t e s were a c t u a l l y Fe3C formed

by

a g r a p h i t ? c r u c i b l e used i n sample p r e p a r a t i o n .

Moreover, a c c o r d i n g t o r e c e n t Fe-Massbauer measurements made a t 4.2K by K l e i n e t

al.,

t h e r e i s a d e f i n i t e d i f f e r e n c e i n Fe atom environments between CuFe (2% Fe) and CuAuFe ( 1 and 3 Fe) a l l o y s : Fe a t a n s i n Cu Au Fe and Cu Au Fe3 a r e domi- n a n t l y 0 8 0 % f e r r o m a g n e t i c , whereas Fe a t a n s in68ug~Be21manifesf7anlPferranagnetic i n t e r a c t i o n s ( < I CR f e r r o m a g n e t i c 1. The d e t a i l e d r e s u l t s w i l l be p u b l i s h e d e l s e - where.

To c l a r i f y whether t h i s d i f f e r e n c e i s due t o a l a t t i c e parameter s h i f t o r a s t r u c t u r a l change, 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 , X-ray a b s o r p t i o n and f l u o r e s c e n c e measurements have been made on t h e s e t h r e e a l l o y s .

Experimental

The samples Cu Fe , Cu Au Fe and Cu Au Fel were m e l t e d , r o l l e d , and- ann- e a l e d t o d i s s 0 l v 2 ~ a l f the6$e 2!om2: T h i s B Z n e 3 i n g c o n t i n u e d f o r 2 4 h o u r s a t 1 0 0 0 ~ ~ f o r Cu 8Fe2 and a t 9 0 0 ~ ~ f o r Cu Au Fe and Cu Au F e l . Then, t o i n d u c e t h e p r e c p i t a t % n . cu Fe and ~ u ~ 30 samp ~ 3 e s were68urtRer annealed f o r 120 ~ u ~ ~ 8 ~ ~ m i n u t e s a t 6 2 0 ' ~ and9&he2~$gAu30 el sample was a n n e a l e d f o r 2 d a y s a t 5 4 0 ~ ~ . Melting and a n n e a l i n g p r o c e s s e s were done i n a q u a r t z t u b e under H2-atmosphere.

The samples were quenched a f t e r a n n e a l i n g by dropping q u a r t z t u b e s i n t o c o l d w a t e r . The Fe K-edge XANES and EXAFS measurements have been made o n t h e s e samples u s i n g t h e beamline X-11A a t t h e N a t i o n a l Synchrotron L i g h t Source a t Brookhaven N a t i o n a l L a b o r a t o b . Eluorescence, a s w e l l a s t r a n s m i s s i o n , d a t a have been o b t a i n e d f o r t h e sample a l l o y s , and t r a n s m i s s i o n d a t a have been o b t a i n e d f o r t h e s t a n d a r d Fe and N i f o i l s a t t h e c o r r e s p o n d i n g K edges. These d a t a have been t a k e n w i t h s i l i c o n (111) monochromator c r y s t a l s i n a two-crystal mode.

R e s u l t s and D i s c u s s i o n

I n F i g . 1 , t h e Fe K-edge XANES s p e c t r a f o r t h e t h r e e samples a r e shown i n compar- i s o n w i t h t h e XANES f o r p u r e Fe. The XANES f o r Cu Au Fe o r Cu6 though s l i g h t l y broadened and d i s t o r t e d , still l o o k s simdir 28 t z a t f o r 8 u r e Fe. The broadening is more pronounced f o r t h e 1% Fe sample. Whereas t h e XANES f o r Cug8Fe2 c l o s e l y r e s e m b l e s t h e

N i

K-edge XANES spectrum f o r f c c N i . These s p e c t r a have been o b t a i n e d from t h e f l u o r e s c e n c e d a t a by p r o p e r background s u b t r a c t i o n s and a normal- i z a t i o n . The c o r r e s p o n d i n g t r a n s m i s s i o n d a t a e x h i b i t e d poor q u a l i t y s p e c t r a w i t h s p u r i o u s s c a t t e r peaks which r e n d e r e d t h e background s u b t r a c t i o n extremely d i f f i - c u l t . e x c e p t i n t h e c a s e of Cu and t h u s are n o t shown here. When t h e l a t t i c e parameter changes w i t h i n t h e &e s t r u c t u r e i n a n a l l o y system, t h e change i s known t o result i n energy s h i f t s o f f e a t u r e s i n t h e c o r r e s p o n d i n g XANES ( 8 ) .

However such a d r a s t i c d i f f e r e n c e i n e l e c t r o n i c s t r u c t u r e , a s shown i n t h e com- p a r i s o n of t h e Fe K-edge XANES s p e c t r a f o r Cu-Fe and Cu-Au-Fe a l l o y s . i s n o t expected t o result from a mere change i n t h e l a t t i c e parameter.

T h e r e f o r e i t is concluded t h a t t h e XANES s p e c t r a f o r t h e Cu-Au-Fe a l l o y s r e f l e c t t h e c l u s t e r i n g o f f e r r o m a g n e t i c bcc Fe, whereas t h e XANES f o r t h e Cu-Fe a l l o y o r i g - i n a t e s from t h e e n v i r o w e n t of a n t i f e r r o m a g n e t i c f c c r - F e . T h i s i n t e r p r e t a t i o n i s a l s o s u p p o r t e d by t h e c o r r e s p o n d i n g s i m i l a r i t i e s m a n i f e s t e d i n t h e EXAFS spec- t r a . I n Fig. 2 , t h e normalized Fe K-edge EXAFS d a t a f o r Cu 8Fe2 o b t a i n e d

by

f l u o r e s c e n c e and t r a n s m i s s i o n measurements a r e shown i n com8arison w i t h t h e normal- i z e d N i K-edge EXAFS f o r Dure

N i .

A l l t h e f e a t u r e s i n t h e EXAFS a a r e e w e l l between t h e f l u o r e s c e n c e and t r a n s m i s s i o n d a t a e x c e p t t h a t t h e r e i s a s l i g h t d i f f e r e n c e i n a m p l i t u d e ( 9 ) . The s i m i l a r i t y observed i n t h e f i g u r e s t r o n g l y s u g g e s t s t h a t t h e environment of Fe a t a n s i n Cug8Fe2 is t h a t of f c c .

Moreoversas shown i n Fig. 3 , when t h e F e K-edge XANES spectrum f o r Cu Fe2 i s compared w i t h t h e N i K-edge XANES f o r p u r e N i , a s h i f t of f e a t u r e s t o w a 8 l o w e r energy which c o r r e s p o n d s t o a l a r g e r l a t t i c e parameter i s observed. T h i s i s con- s i s t e n t w i t h t h e f a c t t h a t t h e r e p o r t e d l a t t i c e s p a c i n g o f Y - ~ e i s 3.5908 ( 3 )

O r

3.5888 ( 4 ) . w h i l e t h a t of f c c N i i s 3.52388.

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m. 1. Fe K-edge XANES s p e c t r a : a. 2. ( a ) Fe KEXAPS f o r Cug8Pe2 ( P ) . ( a ) ( F l u o r e s c e n c e ) . ( b ) Fe K EXAES f o r Cug8Fe2 (T) .

( b ) ~ u ~ ~ ( P ) , * u ~ ~ ~ ~ , ( c )

N i

K-edge EXAES f o r pure

N i

( T ) . ( 0 ) Cu Pe

( d ) p z ! d (Transmission).

V )

0. 10

ENERGY. E i O .

m. 3. S o l i d l i n e : Fe K-edge XANES f o r Cu Pe ( F l u o r e s c e n c e ) . Dotted l i n e :'fii k e d g e

XANES f o r pure N i (Transmission).

a. 4. ( a ) Pe K-edge EXAFS f o r Cu Au Pe ( F l u o r e s c e n c e ) .

(bq7Pe3ke$ge EXAES f o r pure Pe ( T ) .

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C8-1040 JOURNAL DE PHYSIQUE

A

s t r i k i n g s i m i l a r i t y betwen t h e Fe K-edge EXAFS f o r Cu67Au30Fe3 measured i n f l u o r e s c e n c e and t h a t f o r pure Fe i s a l s o shown i n Fig. 4. Hence, t h e XANES and EXAFS r e s u l t s i n d i c a t e t h a t most Fe a t m s i n t h e Cu-Fe a l l o y a r e i n a n t i f e r r m a g - n e t i c f o c -Fe environments, while those i n t h e Cu-Au-Fe a l l o y s a r e i n ferromag-

t i c bcc d - F e environments, which i s i n good agreement w i t h t h e r e s u l t of r e c e n t 'Fe MGssbauer measurements by Klein e t a l .

F i n a l l y , d e f i n i t e supporting evidence f o r t h i s is found i n t h e F o u r i e r trans- forms of t h e Fe K-edge EXAFS f o r t h e s e a l l o y s shown i n Fig. 5. The F o u r i e r trans- form of t h e normalized Fe K EXAFS f o r Cu Au Fe compares very well with t h a t f o r pure Fe obtained

by

Fourier transforming6~he3&raamission d a t a with a s i m i l a r k range, though t h e amplitudes cannot

be

d i r e c t l y compared ( 9 ) . Whereas, a s shown i n Fig. 6 , t h e F o u r i e r transform of t h e normalized Fe K EXAFS f o r Cu Fe compares r e l a t i v e l y w e l l w i t h t h a t of t h e N i K EXAFS f o r pure N i w i t h a s i j h a ? transfomna- t i o n range. The Fournier transform f o r Cu Fe shows more m e a r e d out higher s h e l l peaks which correspond l e s s w e l l i? t h e c$jar$son. This may be t h e r e s u l t of var- ying s i z e s of r - ~ e c l u s t e r s r e p o r t e d by Window (5).

m. 5. F o u r i e r transform ( k weighted)

3

q. ^6. S o l i d l i n e : F o n r i e r transform of t h e normalized Fe K-edge EXAFS: ( k weighted) of the normalized Fe Sol i d 1 ine-Cu An Fe (Fluorescence) K-edge EXAFS f o r Cu98FeZ(Transmission) Dotted line-p%e 28 ( h a n s m i s s i o n ) . Do t e d l i n e : F o u r i e r transform

(kf weighted) of the normalized N i K-edge EXAFS f o r pure N i (Transmission).

Acknowledgments

T h i s r e s e a r c h was supported

by

USDOE under c o n t r a c t numbers, DE-AS05-80ER10T42 and DE-AC02-76CH00016. Support was a l s o received by t h e University of Connecticut Research Foundation. T h i s work was c a r r i e d o u t a t t h e National Synchrotron Light Source.

References

( 1 ) Metals Handbook, ASM. Cleveland (1948) 1196.

( 2 ) F. B i t t e r and A. R. Kaufmann, Phys. Rev., 54 (1939) 1044.

( 3 ) J. B. Newkirk, AIME Trans., .2C9 (1957) 1214.

( 4 ) S. C. Abrahams, L. Guttman and

J.

S. Kasper, Phys. Rev., .l2Z (1962) 2052.

( 5 ) B. Window, P h i l . Mag., 26 (1972) 681.

( 6 ) U. Gonser, K. Krischel and S. Nasu, J. Mag. Mag. Mat., 15-18 (1980) 1145.

(7 0. Schneeweiss, U. Gonser and H. G. Wagner, Scr. Metall., fL

(

1983) 463.

( 8 )

J.