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EXAFS SPECTROSCOPY OF AMORPHOUS Fe-Ni
STEELS
M. de Crescenzi, A. Balzarotti, F. Comin, L. Incoccia, S. Mobilio, D. Bacci
To cite this version:
JOURNAL DE PHYSIQUE CoZZoque C8, supple'nrent au n09, Tome 4 1 , aoct 1980, page C8-238
E X A F S SPECTROSCOPY OF AMORPHOUS Fe-Ni STEELS
* X
N. D e Crescenzi, A.BalzarottiX, F. cornin*, L. 1ncocciaX, S . t<obiliox and ll. Sacci
I>ipartimento d i Fisica, Cniver.si t d de l Za CuZabria, Cosenza, ItaZy
.
.,
Gruppo P. U.L.S., k z b o r a t o r fiJuziona2i d i Frascati, Frascati, ItaZy. Cen tro Richerche FTAT, Orbassano, I t a l y .A b s t r a c t .
-
tie h a v e i n v e s t i q a t e d t h e l o c a l d i s o r d e r o f FeB0Bz0 a n d Fe40Ki40B6F14 q l a s s e s . T h e a s y m m e t r i c 2 e a k o f F ( r ) o b t a i n e d f r o m EXAFS ( E x t e n d e d X-Ray A b s o r p t i o n F i n e S t r u c t u r e ) s t u d i e s i s b e l i e v e d t o b e due t o a s i z e a b l e b e c k s c a t t e r i n g c o n t r i - b u t i o n o f t h e m e t a l - m e t a l p a i r s . T h e m e t a l - n i e t a l l o i d a r r a n g e m e n t c a n n o t be d e f i n i t e l y a s s i g n e d u s i n g t h e EXAFS d a t a a l o n e . Near-edge K - a b s o r p t i o n s p e c t r a S u p p o r t a S t r O n r ~ h y b r i d i z a t i o n i n v o l v i n g t h e d-p b a n d s o f m e t a l a n d B ( o r P ).
I n t r o d u c t i o n . - Amorphous metals ?el-B1-x and Nil-Pl-x and t h e i r a l l o y s h v e i n t e r e s t i n g m e t a l l u r - g i c a l p r o p e r t i e s , sucti a s low c o r r o s i o n , h i @ e l a s t i - c i t y and low o x i d a t i o n ? a t e . \"nether (and t o what extent,) t h e s e p r o p e r t i e s m e determined by t h e l a t t i c e d i s o r d e r has been t h e s u b j e c t o f a number of t h e o r e t i c a l and experimental i n v e s t i g a t i o n s { I } .
The dense randorr packed-hard sphere m d e l (DRPHS) o r i g i n a l l y proposed f o r t h e l i q u i d s t a t e has been a p p l i e d t o -nonoatomic amrphous and l i q u i d t r a n s i - t i o n metals and has provided a d e s c r i p t i o n o f t h e r a d i a l d i s t r i b u t i o n f'unction (FZF) obtained frorn x-
m y d i f e a c t i o n measurements 12,151
.
5 s technique when a p p l i e d t o p d - S i g l a s s e s g a v e r i s e t o a s p l i t t i n g o f t h e f i r s t p e a k o f t h e R D F . G a s k e l 1 { 4 1 d e v e l o p e d a n e x t e n d e d v e r s i o n o f t h e DRPAS model a n d i n t e r p r e t e d t h i s s e p a r a t i o n a s d u e t o m e t a l - m e t a l a n d m e t a l - m e t a l l o i d c o o r d i n a t i o n s p h e r e s . T h i s s p l i t t i n g i s n o t o b s e r v e d when Fe o r fi i s a l l o y e d w i t h B o r P I 5 , 6 } p r o b a b l y b e c a u s e o f t h e r e d u c e d i o - n i c r a d i u s o f t h e m e t a l a n d / o r o f t h e low s c a t t e r i n g f a c t o r o f t h e m e t a l l o i d .i'he EL'--'X teck..-Lo,;? h r s n'sc be(..? used t n i r v e s t i - g a t e t h e l o c a l e n v i r o m e n t o f s e v e r a l binary g l a s s e s . In t h e c a s e o f t h e W-Ce
{7}
system convincing evi- dence was obtained t h a t t h e chemical bonding o f g e r - M u m with palladium i s not s u b s t a n t i a l l y a l t e r e din t h e amorphous p b s e . This r e s u l t does not f i t a random packing m d e l which r e q u i r e s approximately
t i o n o f m e t a l l o i d atoms around t h e metal. Some i n d i - c a t i o n s o f a p r e f e r r e d P-Fe and B-Ni bonding i s
provided by t h e t h e m 1 b e h a v i o w o f t h e RDI".
S u p p l e m e ~ t a l i n v e s t i g a t i o n s a r e t h u s needed t o e l u - c i d a t e t h e p o i n t . The p r e s e n t paper i s concerned with m a s u r e n e n t s o f both near-edge and EXPJ'S a b s o r
-
p t i o n f o r Fe80i320 and Fell'i40B6P14 m e t a l l i classes
The observed a s y m e t r y o f t h e first peak o f RD7 i n t h e s e mnpounds i s c o n p a t i b l e with a b e a t i n g be-tween two m e t a l l i c s c a t t e r i n g s h e l l s surrounding t h e e x c i t e d metal atom (Fe o r PJi). The rneta:.loid s h e l l s may c o n t r i b u t e t o t h e weak s a t e l l i t e s o f t h e main peak i n a p e e m e n t w i t h t h e DRPHS rmdel.
Experiments and r e s u l t s .
-
?'he samples i n t h e form of t h i n ribbons obtained by t h e s p l a t c o o l i n g tech- nique were reduced t o a f i n a l t h i c k n e s s o f2
1 0 uI I
7000 8000 9000
PHOTON ENERGY ( e V )
two n e a r e s t neighbows Ge atoms t o palladium. The Fig.1-Absorption coefficientspectraofFe~0h!i40B6P14
a t t h e Fe a n d Ni K e c l g e s .
Fe-Ni m e t a l l i c g l a s s e s and t h e i r a l l o y s with B and
P were s t u d i e d by klong e t a1
.
{8)
with EXP9S. 3 o m i n o r d e r t o achieve t h e b e s t s i g m l - t o - n o i s e r a t i o . t h e i r r e s u l t s it i s n o t easy t o d i s c r i m i m t e The measurements were performed a t t h e PULS x-ray between a random and a chemically ordered d i s t r i b u - f a c i l i t y u s i n g t h eP
!
s t o r a g e r i n g of ?-ascatiLaboratory. Details o f t h e experimental set up mci
d a t a processiry~ w i l l be reported elsewhere
.
F i q u r e 1 shows t h e Fe a n d Ni K-edrje a b s o r p - t i o n o f t h e a l l o y Fe40Ni40B6P14. I n the f o - l l o w i n g we a n a l y z e t h i s one a s r e p r e s e n t a - t i v e o f d a t a p r o c e s s i n g . T h e K-edges o f Fe and Ni a r e s u f f i c i e n t l y w e l l s e p a r a t e d t o a l l o w t h e EXAFS s t r u c t u r e o f b o t h e d g e s t o be i s o l a t e d w i t h g r e a t a c c u r a c y . The s t r u c - t u r a l . i n f o r m a t i o n i s c o n t a i n e d i n t h e redu- c e d f u n c t i o n K . X ( K ) = [ v ( K ) - y .(K)] /U . ( K ) which i s p l o t t e d i n f i g u r e 2 f o r Pe . p o ( K ) r e p r e s e n t s Pig.2-K-X(K) f o r % i n Fe4$Ji40B6?14; t h e d o t t e d l i n e is t h e backfourier transform of t h e f i r s t peak of t h e F ( r ) .
t h e mnotonic atomic absorption of t h e i s o l a t e d atom. The c o r r e s ~ n d i n ~ r , P ( r ) as c a l c u l a t e d by
b r i e r t m s f o r m i y : K.x(K) a r e reported i n Fiz. 3.
It i s apparent t h a t t h e P ( r ) con.5isLS of a l a r g e 0
asymnetric peak centered a t 2.00
*
.02 A and of' 0 minor s a t e l l i t e s t r u c t u r e l y i n g between 3 and 4 A. T h i s v a l u e d i f f e r s from t h e X-ray d i f f r s c - 0 t i o n by -54 A { 10) t h a t i s t h e p h a s e s h i f t c o r r e c t i o n t o EXAFS d a t a ; B y i n v e r t i n 9 t h e PDF between 1 .1 a n d 2 .&? A w e h a v e i s o l a . t e d t h e X ( K ) .K c o n t r i b u t i o n o f t h e f i r s t n e i q h - b o u r i n g s h e l l s . The e n v e l o p e f u n c t i o n sA(K)
.K, f i g u r e 4 , fo; b o t h Fe a n d Eli d i s p l a y-
1minima a t Kmin
2
1 1 A which a r e c h a r a c - t e r i s t i c o f a b e a t i n g p r o c e s s { l l } .Fig. 3-Fourier transform P ( r ) f o r Fe and N i i n "110~i~0B6P14~
Fig.4-Backscattering amplitude obtained from t h e backfourier transform of t h e f i r s t peak of t h e P ( r ) f o r t h e Fe and N i i n Fe401Ji40B6P14.
It can be r e a d i l y shown08) t h a t t h e d i f f e r e n c e i n t h e bond l e n q t h of two ineouival.ent s h e l l s , AR, i s given by :
AR=(n7; - L I Q ) / ~ K * ~ ( 1 )
where A @ =
- e 2
i s t h e c o r r e s p o d i n g t o t a l phase d i f f e r e n c e o f t h e beating neiybbours. Ey i n s e r t i n qC8-240 JOURNAL DE PHYSIQUE
0
s p l i t t i n 2 o f .65 2 .05 A f o r a l l o y s F e 4 0 M 4 0
B 20 a n d FetO NiqOP 2O a l l o y s ( 8 )
.
Our v a l u e o f .60+
.05 A f o r Fe 40Mi40B6P14 a g r e e w e l l w i t h p r e v i o u s e s t i m a t e s . FeeoB2~ A.?&,=.43
0 A%e-ne=-15 A -""40"i4~B6P14 r e edpe N i e d ~ e A % ~ - ~ = . 44 0qJi-,=.
45
A 0 0 A%e-P=. 27 A A%i-o=-2?A
. l 2@$1i-,=.15
1
0 0 bS,e-7e=-14 A AR,Ji-Ni=.13 Af f e r e n c e o f .29 A between Ni-h'i and Ni-,D se-
p a r a t i o n s . T h e s e r e s u l t s s u ? ? o r t t h e DRPHS 71% l l : ~ 1120 7l30 r:.o
PriJTON EWE?rJY I e V l
s t r u c t u r e o f P o l k , made up by p l a c i n g t h e P
L':
%ble
I
Combining x-ray and n e u t r o n s c a t t e r i n q mea-
s u r e m e n t s i n Ni-P a n d Co-P a l l o y s , Sadoc and z 0
.-*
I-
D i x m i e r I 1 3 1 f o u n d a d i f f e r e n c e between t h e G
0 0 cc
Co-Co a n d Co-P d i s t a n c e s o f - 2 3 A . From t h e s e m
m
d a t a P o l k a n d Bo2dreaux ( 1 4 ) e s t i m a t e d a d i - <
i n t h e v o i d s o f a d e n s e random p a c k i n g a r r a n - gement o f m e t a l a t o m s .
Our ARlg-pand hRFe-p bond l e n g t h s ( t a - b l e I ) a r e n o t t o o d i f f e r e n t from t h e above v a l i ~ e s . F u r t h e r m o r e A s e e B a n 6 ARNi-B a q r e e r a t h e r w e l l w i t h t h e Pe-C a v e r a g e d i s t a n c e d e t e r m i n e d i n c r y s t a l l i n e Fe3C ( 1 5 1 w h e r e t h e C atoms a r e known t o b e t h e n e a r e s t n e i - g h b o u r s t o Fe
.
A metal-rr.etal1oi.d b e a t i n g i s , however, u n l i k e l y s i n c e t h e w e i g h t e d back- Fe 8 80 i00&
s c a t t e r i n g a m ~ l i t u d e o f t h e l i g h t components v a n i s h e s a t l a r g e K . I n d e e d , a d i r e c t model c a l c u l a t i o n o f X ( K ) . K based. o n t h e o r e t i c a l p h a s e s h i f t sI 1
21 a n d a v e r a g e d c o o r d i n a t i o n s p h e r e s i s c a p a b l e o f r e p r o d u c i n g a b e a t i n g f o r t h e r c e t a l - m e t a l p a i r s o n l y . Hence, i n t h i s c a s e i t i s d i f f i c u l t t o c o n s t r u c t t h e d e f i n i t i v e s t r u c t u r a l model f o r t h e Fe atom f i r s t s p h e r e u s i n p EU-FS i n f o r m a t i o n , a t l e a s t w i t h i n t h e l i m i t s o f t h e p r e s e n t ana- l y s i s . T h e a t o m i c e n v i r o n m e n t a r o u n d i r o n o r n i c k e l , which i s S u q g e s t e d from t h e p r e - Big.5-Fe a b s o r p t i o n e d g e s i n b c c Fe a n d Fe80B 20 'Fig.s 5 and 6 show the K - a b s o r p t i o n n e a r e d q e structure f o r the amorphous alloys compared with t h a t of c r y s t a l l i n e Fe. It i s evident t t ~ t the addition of B or P causes a strong reduction i n in-
tensity of the f i r s t peak a t the edge. This inten-
s e n t m e a s u r e m e n t s , c o n s i s t s o f two i n e q u i - v a l e n t s u b s h e l l s o f m e t a l s b e a t i n q b e t w e e n t h e m . T h e d o u b l e t a p p e a r i n g a t 3 .15 a n d
0
3 .75 A f o r Fe a n d less c l e a r l y f o r
EL
h a s PHOTON ENERGY f e V ) b e e n r e p e a t e d l y r e p o r t e d f o r amorphous meta-l l i c a l l o y s u s i n g d i f f r a c t i o n methods I10).
Pig.6-F'e absorption edges and first derivative i n The i n t e r p r e t a t i o n based o n t h e DRPHS model
s i t y r e d u c t i o n may be a t t r i b u t e d t o a c M g e t r a n - s f z r ~ Y o m 1 e t a l l o ' d 'n Fe at-:! c w ~ e ' ? g 2 decmf?c.e o f t h e empty d e n s i t y o f s t a t e s of t h e metal {161. The d e t a i l e d c a l c u l a t i o n s o f Smulowicz and Fease
I171 i n d i c a t e a p-like c h a r a c t e r f o r t h e s e e l e c t r o - n i c s t a t e s j u s t above t h e Fermi l e v e l .
Acknowledgements
-
Ye a r e indebted t o M. Capozi,F. Campolungo, L. 'foretto and t h e machine s t a f f of ADO?IE f o r t h e i r t e c h n i c a l a s s i s t a n c e .
References
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B
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4 . T3.Y. Gaskell, & i d l y [benched F e t a l s 111,
2
(1978) 277.5. T. %kunage e t a l . , idly %enched Metals 111,
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6 . J. LO,^, Phys. S t a t . S o l . ( a )
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