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Submitted on 1 Jan 1979
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MÖSSBAUER ANALYSIS OF GRAIN BOUNDARIES AS A FUNCTION OF THE GRAIN BOUNDARY
STRUCTURE
H. Ichinose, M. Hashimoto, Y. Ishida
To cite this version:
H. Ichinose, M. Hashimoto, Y. Ishida. MÖSSBAUER ANALYSIS OF GRAIN BOUNDARIES AS A
FUNCTION OF THE GRAIN BOUNDARY STRUCTURE. Journal de Physique Colloques, 1979, 40
(C2), pp.C2-542-C2-543. �10.1051/jphyscol:19792187�. �jpa-00218564�
JOURNAL D E PHYSIQUE Colloque C2, suppldment au n O 3, Tome 40, mars 1979, page C2-542
MOSSBAUER A N A L Y S I S O F G R A I N B O U N D A R I E S A S A F U N C T I O N OF T H E G R A I N BOUNDARY STRUCTURE
H. Ichinose, M. Hashimoto and Y. Ishida
I n s t i t u t e o f Industriai! Science, U n i v e r s i t y o f Tokyo, 7 Roppongi, Minatoku, Tokyo, Japan
R6suG.- Des bicristaux et polycristaux d'argent contenant des traces de '"~n aux joints de grains ont dte examines par spectromdtrie Mgssbauer. Les premiers rdsultats indiquent que pour les fai- bles ddsorientations, le spectre est sensiblement celui de "'~n en solution solide avec une lar- geur de raie plus petite que pour des Echantillons polycristallins.
Abstract.- Both polycrystalline and bicrystalline silver foils with a small amount o f l l g m ~ n sand- wiched in the boundary were produced and the Miissbauer spectra were recorded. The preliminary re- sult on small angle boundaries showed that the main spectrum position was near that of solid solu- tion 'lgmsn and the line width was smaller than that of polycrystalline specimen.
1. Introduction.- In order to develop grain boundary theories on a sound basis, information of the grain boundary structure and of the electrical and lattice dynamical properties cannot be dispensed with.
The most powerful technique currently available for thegeometrical information is high resolution high voltage electron microscopy / l / while electrical and lattice dynamical information is obtained re- cently by Gssbauer effect for fine grained speci- mens of Zn-A1 eutectoid /2/ and iron /3/. It was found that llgmsn atoms segregated in the grain boundary is bonded less tightly with surroundings.
It was also found in iron specimen that "'m~n in the grain boundary does not feel any internalmagne- tic field. One of the draw back of the above expe- riment was the mixture of the boundary structure investigated by the technique; it offers only the average information of all the existing grain boun- daries with certain weight factor to more strongly segregated ones. In order to get rid of the comple- xity the investigation of a bicrystal is indispen- sable.
2. Experimenta1s.- As the substrate a pair of rock salt crystals with an area 2cm X 2 cm and 2 m thick were clevaged and the (100) surface was polished.
The rock salt substrates were mounted in a vacuum chamber kept at 1.33 X 10-'Pa and heated after evacuation. Silver purity 99.999 % was evapo- rated on the substrates in vacuum of 6.7 x I O - ~ P ~ and at 520 K to grow epitaxially single crystals of silver. Silver was evaporated again for the second time in vacuum 1.33 x 10-'pa at 520 K to prepare clean single crystal surfaces of silver. A small amount of "'Wn was evaporated on the surface and the two crystals were pressed to each other immedia-
tely. The bicrystal foil was dried and placed in a cryostat. The l6ssbauer source experiment was per- formed using Elscint AME 31 spectrometer by vibra- ting the standard absorber BaSnO,.
The specimen was held at temperatures between liquid nitrogen and room temperature. The Mgssbauer spectrum was analyzed using FACOM 230-55 computer by non-
linear least square method.
3. Result.- Figure ](a) shows an example of the Mgss bauer spectrum of
'
" m ~ n evaporated on an Ag poly- crystalline foil on which another layer of silver thickness of 3a50nm evaporated at 370 K.Fig. I (a) : Mgssbauer spectrum of l 1 g m ~ n in the polycrystalline foil.
The amount of 'lgmsn in the specimen is about 10'' atoms/cm2, which corresponds approximately to ten layers of tin sandwiched in the boundary. The iso- mer shift of the spectrum, however, showed that neither B phase tin particles nor solid solution tin was produced. The majority of tin atoms seems to re- main in the boundaries of silver. A small amount of snY+ component appeared to the left of the main peak. Figure I(b) shows the spectrum due to llgmsn
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792187
i n a s m a l l a n g l e t w i s t boundary 0 = 10' o f s i l v e r b i c r y s t a l . The s p e c t r u m i n d i c a t e s t h a t
'
lgmsn i n t h e g r a i n boundary i s n o t a g g l o m e r a t e d e v e n though t h e specimen was h e l d a t 520 K .F i g . I ( b ) : bfdssbauer s p e c t r u m o f l l g r n s n s e g r e g a t e d i n s m a l l a n g l e t w i s t boundary 0 = 10'. The p o s i t i o n s A , B and C c o r r e s p o n d t o t h o s e o f i o n i c , s o l i d so- l u t i o n and B p h a s e t i n r e s p e c t i v e l y .
The p o s i t i o n o f t h e main peak i s n e a r t h a t o f s o l i d s o l u t i o n l ' g m ~ n i n s i l v e r a s i s e x p e c t e d f o r a s m a l l a n g l e boundary. I f t e n d e g r e e t w i s t bounda- r y c o n s i s t s of two s e t s of screw d i s l o c a t i o n s 9nm a p a r t , m a j o r i t y o f ' ' g m ~ n atoms s h o u l d b e n e a r t h e d i s l o c a t i o n b u t n o t a t t h e c o r e . The d i s t o r t i o n o f atoms around d i s l o c a t i o n i s l o n g r a n g e d b u t t h e e l e c t r o n i c s t a t e i s n o t l i k e l y t o b e l a r g e l y d i f f e - r e n t from t h a t o f t h e p e r f e c t c r y s t a l .
R e f e r e n c e s
/ l / I s h i d a , Y . and I c h i n o s e , H . , " P r o c e e d i n g s o f I n t . N a t i o n a l Congress o f HVEM (1977) Kyoto.
/ 2 / Y s h i d a , Y . , and Ozawa, T . , S c r . Met.
9
(1975) 1103./ 3 / Ozawa, T., and I s h i d a , Y . , S c r . Met.
