MÖSSBAUER SPECTROSCOPY OF DIFFERENT INTERSTITIAL COMPOUNDS AND SOLID SOLUTIONS CONTAINING 57Fe

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MÖSSBAUER SPECTROSCOPY OF DIFFERENT INTERSTITIAL COMPOUNDS AND SOLID

SOLUTIONS CONTAINING 57Fe

J. Foct, J. Senateur, J .M. Dubois, Gérard Le Caër

To cite this version:

J. Foct, J. Senateur, J .M. Dubois, Gérard Le Caër. MÖSSBAUER SPECTROSCOPY OF DIFFER-

ENT INTERSTITIAL COMPOUNDS AND SOLID SOLUTIONS CONTAINING 57Fe. Journal de

Physique Colloques, 1979, 40 (C2), pp.C2-647-C2-649. �10.1051/jphyscol:19792225�. �jpa-00218606�

JOURNAL DE PHYSIQUE

Colloque C2, suppl&ment au n o 3, Tome 40, mars 1979, page C2-647

MOSSBAUER SPECTROSCOPY OF D I FFERENT I N T E R S T I T I A L COMPOUNDS AND SOLID SOLUTIONS CONTAINING 5 7 F e

J . F o c t , J . P . s e n a t e u r Y , J.M. ~ u b o i s * ~ and G. Le c a e r f X

Laboratoire de MdtaZZurgie Physique, Universitd des Sciences e t Techniques de L i l l e , B.P. 36 59650 ViZZeneuve drAscq, France.

*I.N.P. C., Cknie Physique, B.P. 25, 38040 CrenobZe, France

"'~aboratoire de MdtaZ Zurgie, Eco Ze des Mines, 54042 Ncmcy, France

Rdsum6.- Les v a r i a t i o n s des paramPtres h y p e r f i n s du f e r s o n t d i s c u t d e s dans l e s s o l u t i o n s s o l i d e s i n t e r s t i t i e l l e s , l e s c a r b u r e s e t l e s n i t r u r e s .

A b s t r a c t . - The h y p e r f i n e parameters of i r o n a r e d i s c u s s e d i n i n t e r s t i t i a l s o l i d s o l u t i o n s , c a r b i - des and n i t r i d e s .

The aim of t h i s paper i s t o d i s c u s s t h e h y p e r f i n e of i n t e r s t i t i a l c o n t e n t w h i l e Fe

-

N d i s t a n c e s a r e

0

parameters of i r o n i n i n t e r s t i t i a l s o l i d s o l u t i o n s about 1.9 A. From experimental r e s u l t s 13, 41 we and compounds. The compact f . c . c . and h.c.p. s t r u c -

t u r e s where i n t e r s t i t i a l s I ( I = B , C , N) a r e i n o c t a h e d r a l s i t e s a r e considered and a l s o the com- pounds where I a r e a t t h e c e n t r e s of t r i g o n a l prisms.

I n t h i s l a s t c a s e t h e s t r u c t u r e a r e c l a s s i f i e d a s a f u n c t i o n of t h e i n c r e a s i n g l i n k a g e c o e f f i c i e n t I l l . The m a r t e n s i t e s a r e excluded from t h e d i s c u s s i o n a s t h e i r ~ E s s b a u e r s p e c t r a c r e a t e many problems which a r e not f u l l y r e s o l v e d .

1 . Hyperfine f i e l d s and isomer s h i f t s . - A s a l r e a d y noted t h e e f f e c t of t h e m e t a l l o i d atoms on t h e i r o n atoms should be of s h o r t range and t h e v a r i a t i o n s of t h e h y p e r f i n e f i e l d s may be r e l a t e d t o the number ( n ) of i n t e r s t i t i a l neighbours and t o t h e Fe

-

^I

d i s t a n c e s ( r ) : H = H

-

K(r) n

Feu (1)

According t o / 2 / K(r) would vary a s r-3. Experimen- t a l r e s u l t s l e t us re-examine eq. ( I ) c o n s i d e r i n g t h a t K may be d i f f e r e n t f o r B , C , N :

As we only want t o determine the g e n e r a l behaviour, we c o n s i d e r s o l e l y KI t h e p a r t of K ( r . ) which i s

I J

independent of r t h e n i f n i s t h e e f f e c t i v e

j' e f f

number of I neighbours :

HI = Ho

-

KI neff (2)

F i n a l l y a s the h y p e r f i n e f i e l d s a r e g e n e r a l l y un- known atOK..we only c o n s i d e r t h e compounds w i t h high Curie temperatures whose H a r e known a t 77 K.

I n y' and E i r o n n i t r i d e s , each i r o n atom i s s u r - rounded by twelve i r o n neighbours a t a d i s t a n c e which v a r i e s between 2.66

1

and 2.73

1

a s a f u n c t i o n

o b t a i n f i g u r e I which shows t h e hyperfine f i e l d of i r o n a s a f u n c t i o n of the number n

~ ~ ( n ) = 374

-

73 n (kOe) ( c o r r e l a t i o n c o e f f i c i e n t 0.99).

Fig. 1 : Hyperfine f i e l d s i n i r o n n i t r i d e s ( A ) and i r o n c a r b i d e s ( 0 ) a s f u n c t i o n s of t h e number n of i n t e r s t i t i a l n e a r e s t neighbours.

H i s g r e a t e r than HFea a s assumed i n e q u a t i o n 1 / 2 , 5 / and may be a s c r i b e d t o t h e h y p e r f i n e f i e l d of i r o n atoms i n h y p o t h e t i c a l ferromagnetic f . c . c . o r h . c . p . i r o n .

0

I n i r o n c a r b i d e s t h e Fe-C d i s t a n c e s a r e about 2 A.

The i r o n c o o r d i n a t i o n i s 12 i n simple c a r b i d e s and I 1 o r 12 a c c o r d i n g t o t h e i r o n s i t e i n Fe,C and FesC2 where the s c a t t e r i n Fe-Fe d i s t a n c e s i s grea- t e r than i n t h e former c a r b i d e s . The n v a l u e s a r e 2 f o r t h e FeI s i t e s i n Fe,C and F e s % w h i l e f o r t h e Fe11 s i t e s t h e r e i s a t h i r d neighbour a t 2.37 i n

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792225

c2-648

JOURNAL DE PHYSIQUE Fe,C and a t 2.22

;i

i n Fe5& 161. The H I I f i e l d s i n

Fe3C and Fe5& would t h e n c o r r e s p o n d t o n e f f bet- ween 2 and 3, b u t i n a f i r s t a p p r o x i m a t i o n we t a k e n = 3 .

Taking h y p e r f i n e f i e l d s o f & c a r b i d e s 1 7 1 o f Fe3C and Fe5C2 1 6 1 and t h e p o s s i b l e c u b i c FekC c a r b i d e we o b t a i n :

H C ( n ) = 376

-

57 n (kOe)

The H v a l u e s a r e s i m i l a r f o r C and N b u t d i f f e r from t h e v a l u e g i v e n by I n o e t a l . 1 5 1 w h i l e t h e v a l u e s of K may b e compared. I n i r o n b o r i d e s where t h e Fe-Fe d i s t a n c e s v a r y from 2.4 t o 2.72

;i

and where o n l y f o u r v a l u e s a r e a v a i l a b l e I 1 5 1 e q u a t i o n 2 i s d i f f i c u l t t o c h e c k . Adding t h e c o n s t r a i n t Ho = 375 kOe one o b t a i n s

~ ~ ( n ) = 375

-

45 n (kOe)

We c o n c l u d e t h a t t h e l i n e a r r e l a t i o n s h i p HI ( n ) i s q u i t e w e l l f o l l o w e d i n n i t r i d e s , r a t h e r w e l l i n c a r b i d e s and a p p r o x i m a t i v e l y i n b o r i d e s . T h i s beha- v i o u r may b e r e l a t e d t o t h e n a t u r e of m e t a l l o i d atom and t o a w i d e r r a n g e o f Fe-Fe d i s t a n c e s when t h e s t r u c t u r e which i s s i m p l e i n n i t r i d e s becomes more and more complex w i t h c a r b o n and b o r o n . Howe- v e r , a n i m p o r t a n t p a r t of t h e t o t a l h y p e r f i n e f i e l d i s d e t e r m i n e d by t h e l i n e a r v a r i a t i o n s H ( n ) . Compa- I r i s o n o f t h e Mzssbauer s p e c t r a o f E c a r b i d e s and n i t r i d e s shows n e v e r t h e l e s s t h a t t h e e f f e c t o f n i - t r o g e n on H i s mainly r e s t r i c t e d t o t h e f i r s t coor- d i n a t i o n s h e l l w h i l e c a r b o n a c t s on more d i s t a n t n e i g h b o u r s . F i n a l l y , t h e K v a l u e i n c r e a s e s from B

I

t o N r o u g h l y a s d-3 i f d i s t h e s h o r t e s t Fe-I d i s - t a n c e . T h i s does n o t mean t h a t KI, f o r a g i v e n I , v a r i e s a s r-3 b u t may b e r e l a t e d t o t h e bonding pro- p e r t i e s which, i n p a r t i c u l a r , r e f l e c t t h e i n f l u e n c e of t h e s i z e o f t h e i n t e r s t i t i a l .

It i s more d i f f i c u l t t o e x t r a c t a s i m p l e b e h a v i o u r from t h e v a r i a t i o n s o f isomer s h i f t s (6) b e c a u s e t h e second o r d e r ~ E p p l e r s h i f t h a s i n most c a s e s n o t been measured. Only comparison o f v a r i o u s e n v i r o n - ments 6 o f a g i v e n compound seems t o be m e a n i n g f u l : i n n i t r i d e s 6 i n c r e a s e s w i t h n w h i l e i t r e m a i n s n e a r - l y c o n s t a n t o r d e c r e a s e s i n c a r b i d e s and b o r i d e s . I n t h e s i m p l e p i c t u r e where t h e m e t a l l o i d d o n a t e s e l e c t r o n s t o t h e 3d l e v e l s o f Fe w i t h o u t a l t e r i n g them, H d e c r e a s e s and 6 i n c r e a s e s w i t h n a s o b s e r v e d i n n i t r i d e s b u t n o t i n c a r b i d e s and b o r i d e s . The d i - r e c t and i n d i r e c t c o n t r i b u t i o n of 3d and s e l e c t r o n s t o H and

6

does n o t a l l o w t o f u l l y d e s c r i b e t h e bon- d i n g . The donor model h a s been r e j e c t e d i n b o r i d e s 1 8 1 : t h e i r o n d band b e i n g a l t e r e d p r o b a b l y b y

h y b r i d i z a t i o n w i t h boron 2 s and 2p s t a t e s and no e v i d e n c e of boron e l e c t r o n s t r a n s f e r i s found. Fi- n a l l y a l a r g e p o s i t i v e c o n d u c t i o n band p o l a r i z a t i o n i s e x p e c t e d t o c o n t r i b u t e t o H . The bonding e l e c - t r o n s a r e p r o b a b l y more and more d e l o c a l i z e d f r o d t o B. I n n i t r i d e s a n e g a t i v e c h a r g e i s found o n . n i - t r o g e n by s u p e r s t r u c t u r e s r e f l e x i o n i n t e n s i t i e s and t h e c e n t r e of t h e c h a r g e c l o u d i n t h e bonding s t a t e may move towards t h e n i t r o g e n s i t e 19, 10, 1 1

1.

2. Quadrupole s p 1 i t t i n g s . - F r o m t h e r a p i d v a r i a t i o n o f t h e f u n c t i o n r-3, ,where r i s a n e l e c t r o n - n u c l e u s d i s t a n c e , t h e e l e c t r o n s which p a r t i c i p a t e i n t h e s t r o n g Fe-I bonds a r e e x p e c t e d t o g i v e t h e major c o n t r i b u t i o n t o t h e q u a d r u p o l e s p l i t t i n g s measured a t t h e i r o n n u c l e u s . C o n s i d e r i n g t h e a b s o l u t e va- l u e s of t h e q u a d r u p o l e s p l i t t i n g s o f i r o n atoms h a v i n g two i n t e r s t i t i a l n e a r e s t n e i g h b o u r s a t a

0

d i s t a n c e c l o s e t o 2 A i n (Fel-xMx)3C (M = Cr, Mn), (Fel-xMnx)5C2, (Mnl-xFex)5SiC, M3M1C (M = Fe, M, M' = Al, Ga, Ge, Zn, Sn) and i n y' FebN, yFe-C and yFe-N /3,6,12-141 we o b t a i n t h e f o l l o w i n g t a b l e where 8 i n d i c a t e t h e a n g l e of t h e two s h o r t e s t i r o n - i n t e r s t i t i a l bonds f o r e a c h s i t e .

T a b l e

-

One may o b j e c t t h a t t h e FeII s i t e s of Fe3C and Fe5C2 have a t h i r d c a r b o n n e i g h b o u r ( e . g . h y p e r f i n e f i e l d s ) . These t h i r d n e i g h b o u r s a r e e x p e c t e d t o c o n t r i b u t e l e s s t h a n t h e two c l o s e s t c a r b o n neigh- b o u r s b e c a u s e o f t h e v e r y s t r o n g v a r i a t i o n w i t h d i s - t a n c e of t h e o p e r a t o r d e t e r m i n i n g t h e q u a d r u p o l e s p l i t t i n g s . I n t h e c a s e o f Mn5SiC, t h e s i l i c o n n e i - ghbours presumably e f f e c t m a i n l y t h e s e l e c t r o n s ,

Compound

Pe3C un5S ic FesC2

Kn5SiC

Pesc2

Pe3C l l n s S i C Kn3CaC Mn3ZnC Y 'Pe4N

Y re-C Y Qe-N

Y Fe-N

9 (9

09 1 &

100 105 142 144 158 180 180 180

180

A 4 s

0.32 0.28 0.37 0.36 0.80 0.68 0.71 1.5 1.5 0.50 0.64 0.25 0.45 Iron s i t e

"='3 Qe11 '+"4

Fe 1 Fe 1

""2 Yn Yn Fell

I n t e r e t i t i a l - Fe dlstsncs (1) 2.- - 2.04 2.00

-

^{2 . 0 3}

1.08 - 2.01 2 . a

-

^2.05

1.97

-

^1.99

1.87

-

^1.99

2.18

-

^2.32

1.95

-

^1.95

1.96

-

^1.96

1.30 - ^1.90

1.83

Pell

I

1.83

-

^1.83

that is the isomer shift in the paramagnetic state /12/. The quadrupole splittings increase regularly with the angle of the two iron-carbon bonds and are practically insensitive to the metallic neighbour- hood of the iron atoms under consideration /12/.

The comparison of

A

in yfFe,N and the perovskite type carbides shows that A is negative in both ca- ses and that AC

=

3 AN. In MnkN and Mn3ZnC, the quadrupole splittings are such that AC

=

2.8

AN

and in austenite

A =

2.6

A N .

This is further confirmed

C

by the observation of high negative anisotropic fields Ha in MnsZnC and MnsGaC doped with 5 7 ~ e and almost zero anisotropic fields in FekN. As the 3d electron dipolar fields may be responsible for the main part

of

H they are closely related to 6.

a'

These results show that the centre of charge of the bonding electrons is closer to the nitrogen site than to the carbon site, in agreement with the re- sults of Nagakura /9,

101

and with the difference in the electronegativities of C and N.

References

/I/ Parthe, E., and Moreau, J.M., J. Less-Common Metals 53 ⁽¹⁹⁷⁷⁾

^1.

121 Fatseas, G., Phys. Status, Solidi (b) 59 ⁽¹⁹⁷³⁾

K23.

/3/ Foct, J., J. Physique Colloq. 35 (1974) C 6- 487.

/4/ Foct, J., Dubois, J.M., and Le Caer,

G.,

J.

Physique Colloq. 35 (1974) C 6-493.

/5/ Ino, H., Moriya, T., Fujita, F., Maeda, Y., Ono, Y., and Inokuti, Y., J. Phys. Soc. Japan 25 (1968) 88.

-

161 Le Caer, G., Dubois, J.M., and Senateur, J.P.

J. Solid. State Chem. 2 (1976) 19.

/7/ Dubois, J.M., and Le Caer, G., Acta Met. 25 (1977) 609.

/8/ Perkins, R.S. and Brown, P.J., J. Phys. F.4

(1974) 906.

/9/ Nagakura,S., J. Phys. Soc. Japan 2 (1968) 488.

/lo/ Nagakura, S., and Tanehashi, K., J. Phys. Soc.

Japan 2 (268) 840.

/Ill Barberon, M., ThGse Paris (1973).

/12/ Dubois, J.M., Le Caer, G. and Senateur, J.P., J. Solid State Chem. 2 (1978) 2.

/I31 Senateur, J.P., Boursier, D., LfHeritier, P., Lorthoir, G., Fruchart, E. and Le Caer. G., Mat. Res. Bull. 9 (1974) 603.

/14/ Foct, J., C.R. Hebd. Sean. Acad. Sci. 276

(1973) 1159.