EELS ANALYSIS OF A PRECIPITATE IN V3Si BY STEM AND HVEM

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EELS ANALYSIS OF A PRECIPITATE IN V3Si BY STEM AND HVEM

A. Ben Lamine, F. Reynaud, C. Colliex, M. Acheche, Jean Sévely, Yolande Kihn

To cite this version:

A. Ben Lamine, F. Reynaud, C. Colliex, M. Acheche, Jean Sévely, et al.. EELS ANALYSIS OF A PRECIPITATE IN V3Si BY STEM AND HVEM. Journal de Physique Colloques, 1984, 45 (C2), pp.C2-709-C2-712. �10.1051/jphyscol:19842164�. �jpa-00223837�

Résumé - Nous avons effectué l'analyse d'un précipité dans V3Si (structure A15) par spectroscopie de pertes d'énergie en microscopie électronique classique à haute ten- sion (1000 kV) et à balayage (100 k V ) , par transmission. Compte tenu du diagramme de phases du système binaire V-Si, l'analyse a permis de penser qu'il s'agissait de V5Sn'3. Ce résultat a été confirmé par microdiffraction électronique en faisceau convergent.

Abstract - The analysis of a precipitate in V3Si (A15 structure) has been performed by transmission EELS with a HVEM (1000 kV) and with a STEM (100 kV). Taking into account the phase diagram of the V-Si system, the composition VgSij is anticipated.

This result has been confirmed by convergent beam electron microdiffraction.

A new lattice defect has been found /l/ by TEM in the \?5Si3 superconducting compound (A15 structure, Fig. 1). It looks like a couple of dislocation li- nes parallel to the <100> directions and it has been analyzed as a a/2 <100> faulted dipole / 2 / by matching conventional electron micrographs (Fig. 2) with computer simulations. However, resi- dual contrast has been observed /3/ in the case of perfect^theore^ic^al^ extinction of the faulted dipole (g".b = 0, g.bAu" = 0 and A = 0.97 at room temperature ) . It has been first erroneously pos- tulated / 4 / that this defect could be a dispira- tion /5/ dipole. We have then been led to postu- late the hypothesis that the faulted dipole ac- counted for the plastic deformation of the V3Si matrix caused by a needle-shaped precipitate.

The purpose of this communication is to report

the analysis of this precipitate by Electron Fig. 1 - Unit cell of V^Si Energy Loss Spectroscopy (EELS) and convergent ( M 5 s t r u c t u r e ).

beam electron microdiffraction. v '

I - EXPERIMENTAL PROCEDURE

The chemical analysis of the precipitate has been performed by EELS using both the 1.5 MV HVEM of the Laboratoire d'Optique Electronique (L0E) du C.N.R.S. de Toulouse operating at 1 MV /6,7/ and the 100 kV VG-HB501 STEM of the Laboratoire de Physique des Solides d'Orsay /8/. The crystallographic study of the precipitate has been un- dertaken with the 120 kV Philips EM400 of the L.O.E. equipped with a field emission gun.

The precipitate, which is elongated along the <100> directions and the rectangular cross section of which is of the order of 40-80 nm x 10-15 nm is set parallel to the incident electron beam in a - (100) thin foil. The polishing of the samples for elec- tron microscopy has been described elsewhere / 2 / .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19842164

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F i g . 2

-

I1

-

a t 1 MV. The p a r t o f t h e spe- cimen which i s i n v e s t i g a t e d i s l i m i t e d by the s e l e c t i n g a p e r t u r e t o an area o f about 100 nm i n diameter. Such a probe does n o t a l l o w t h e ana-

l y s i s o f t h e p r e c i p i t a t e a l o - 1800

ne ; i t in c l u d e s a l s o a p a r t o f t h e m a t r i x . The presence o f vanadium and s i l i c o n o n l y

has been detected, so t h a t 1 ~ 0 0

t h e p r e c i p i t a t e belongs t o t h e b i n a r y V-Si system, t h e phase diagram o f which i s shown i n Fig. 3. I n addi- t i o n t o t h i s r e s u l t , t h i s technique has shown q u a l i - t a t i v e l y t h a t t h e p r e c i p i - t a t e i s enriched i n s i l i - con w i t h r e s p e c t t o t h e m a t r i x . Taking i n t o account

both r e s u l t s , t h e p r e c i p i - Si 10 20

30

t a t e i s a n t i c i p a t e d t o be

Y-VsSi3 /9/. This r e s u l t Fig. 3 - The b i n a r y V-Si system phase diagram (accor- has been confirmed by EELS d i n g t o /9/) showing t h e t h r e e compounds w i t h t h e STEM and by con- 6-V3Si, Y-V5Si3 and f3 - V S ~ 2.

vergent beam e l e c t r o n d i f - f r a c t i o n .

F i g . 4

-

111 - EELS ANALYSIS OF THE PRECIPITATE BY STEM

I n t h e STEM, t h e e l e c t r o n probe i s h e l d on a given specimen f e a t u r e o r scanned over a reduced area which can be adapted t o t h e geometry and dimensions o f t h e specimen t o be analysed. In t h e present study, an area o f 22 x 15 nm i s i n v e s t i g a t e d , o f t h e m a t r i x , o f t h e c o r r e c t l y o r i e n t e d needle-shaped p r e c i p i t a t e s o r o f t h e depressions

induced by p o l i s h i n g around them. The EELS spectra e x h i b i t several edges f o r vanadium and s i l i c o n . The two low energy edges (V-M23 a t 55 eV and Si-L23 a t 99 eV) cannot be used f o r q u a n t i t a t i o n because they are superimposed on an i n t e n s e background which cannot be adequatly represented by a power law o f t h e form A. A E - ~ . Consequently, one has t o perform t h e measurements from t h e V-L23 edge a t 507 eV and the Si-K edge a t 1855 eV, as shown i n F i g . 5. The atomic r a t i o can be estimated as f o l l o w s :

where S denotes the s i g n a l a f t e r background s t r i p p i n g and a t h e c a l c u l a t e d sigmak and sigma1 cross s e c t i o n / l o / f o r t h e energy ( A ) and angular c o l l e c t i o n o f d e t e c t i o n used.

Two types o f c o r r e c t i o n s have then t o be taken i n t o account, concerning t h e specimen i t s e l f and t h e instrument. The f i r s t a l l o w s f o r t h e i n f l u e n c e o f the s t ng thickness v a r i a t i o n s , which cause m u l t i p l e s c a t t e r i n g c o n t r i b u t i o n s over t h e edge

Bb

-

A f t e r c a l i b r a t i n g t h i s e f f e c t from t h e known composition o f t h e m a t r i x , t h e composi- t i o n o f t h e p r e c i p i t a t e can be e s t a b l i s h e d t o be VxSi w i t h 1.4 4 ~ 5 1 . 6 , which provides a f i r s t c l e a r i d e n t i f i c a t i o n t h a t i t i s V5Si3.

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F i g . 5 - 100 kV STEM EELS s p e c t r a on a p r e c i p i t a t e seen edge-on i n V3Si.

Enlargements o f t h e Lz3 edge o f vanadium ( a ) and o f t h e K edge o f s i l i c o n ( b ) a r e shown, t o g e t h e r w i t h t h e e x t r a p o l a t i o n o f t h e background.

I V

-

F i g . 6 - (012):: convergent beam d i f f r a c t i o n p a t t e r n o f t h e p r e c i p i t a t e seen edge-on i n t h e V3Si m a t r i x . I t corresponds t o t h e q u a d r a t i c V5Si3 phase.

V - REFERENCES

/1/ BEN LAMINE A., REYNAUD F., MA1 C. e t SENATEUR J.P., P h i l . Mag.38 (1978) 359.

/2/ BEN LAMINE A., SENATEUR J.P. e t REYNAUD F., J. Microsc. S p e c t r z c . E l e c t r o n . 5 (1980) 745.

/3/ BEN LAMINE A. and REYNAUD F., 1 0 t h I n t . Conqr. E l e c t r o n Microsc. Hamburg (1982),

, . . .

v o l . 2, 149.

/4/ REYNAUD F. e t BEN LAMINE A., Acta Met. 29 (1981) 1485.

/ 5 / HARRIS W.F., P h i l . Mag. 22 (1970) 949. -

/6/ JOUFFREY B., KIHN Y., P E E 2 J.Ph., SEVELY J. and ZANCHI G., 9 t h I n t . Congr.

E l e c t r . Microsc., T o r o n t o (1978), v o l . 111, 292.

/ 7 / ZANCHI G., SEVELY J . and KIHN Y., J. Microsc. Spectrosc. E l e c t r o n . ,

5

/8/ COLLIEX C., 1 0 t h I n t . Congr. E l e c t r o n Microsc. Hamburg (1982), v o l . 1, 159 o r COLLIEX C., TREBBIA P., U l t r a m i c r o s c o p y 9, (1982) 259.

/9/ M e t a l s Handbook, v o l

.

/ l o / EGERTON R.F., U l t r a m i c r o s c o p y

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/ll/ STEPHENS A.P., U l t r a m i c r o s c o p y

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