560 EXTENDED ABSTRACTS -aO30 r(Si) clSi) -0.025 0 1 2 t~r n i n l 3 OD30 r(Si) m a025 0.020 0.01 5 0 1 2 ~Crninl 3 Figure 1. Sputter depth profiles of phosphorus, nitrogen and silicon for (a) (1 12) grain boundary and (b) (01 3) grain boundary. For a better comparison, the values of the relative peak-to-peak heights of the elements i and Fe (47 eV), r(i), are normalized by the bulk atomic concentrations, c(i).from Fig. l(b), this depletion is observed in the boundary layer only. The repelled atoms remain accumulated near the boundary. On the other hand, the 23 boundaries possess a very dense atomic arrangement with a very small excess of free volume, where less appropriate segregation sites for P can be accessible and a lower P segregation is observed. However, even relatively small deviations of the atomic configurations with respect to the perfect crystal in these cases are sufficient for a substantial increase of the Si concentration at these boundaries. From the point of view of some quantitative differences (low segregation of P and the depletion of Si at the (012) grain boundary), the grain boundary structure seems to be the most important condition controlling their chemical composition.Nitrogen segregates to all grain boundaries studied here and is practically unaffected by the boundary structure. Probably, it occupies the interstitial positions in the boundary, being apparently independent of both the structure of grain boundaries and the amount of other elements segregated there. REFERENCES 1. E. D. Hondros and M. P. Seah, lnt. Metall. Rev. 22, 262 2. C. L. Briant,Acta Metall. 31, 257 (1983).The surface properties of an alloy depend strongly on the surface composition. An Auger study of the silver-palladium system will bring a better understanding of the surface segregation processes in this alloy. The choice of this system is justified by:(1) the industrial applications of silver-palladium coatings(2) the great number of reactions catalysed by palladium;(3) the experience of the laboratory in IbVIIIb binary Two kinds of alloys were studied. In the low palladium concentration range (<20 at.%), we prepared massive single and large-grain crystals of alloys by the Bridgman method. Important solidification structures were detected and studied by Auger microscopy, electron microprobe and micro-(dentistry, electrical contacts, etc.); systems (Cu-Pd, Cu-Rh).hardness tests. An enrichment of palladium on the border of the solidification cells was observed. The centre of the cells was silver enriched.Samples in the whole range of concentrations, and particularly those rich in palladium, were prepared by condeneation of homogeneous epitaxial films of alloys on MgO(100) and NaCl( 100) by glow discharge sputtering. The epitaxial conditions for various systems are summarized in Table 1. Parallel epitaxy (lOO),[Ol 1],,//(100),[01 13, (where d stands for deposit and s for substrate) is always dominant, as observed by reflection electron diffraction. The film structure was also characterized by transmission electron dif...