THEORY OF SEGREGATION USING THE EQUIVALENT-MEDIUM APPROXIMATION AND BOND-STRENGTH MODIFICATIONS AT SURFACES - APPLICATION TO FEE PD-X ALLOYS

We have developed, in the framework of a broken-bond model, a method t o determine the surface composition of transition metal alloys. The mo del is based on the equivalent-medium approximation which allows us to calculate the energies of surface layers as a function of local Conce ntration. The model also considers bond strength modifications at the surface that are determined within a modified tight-binding scheme. Th e model has been applied to several fee Pd-based alloys. The results a re found to be in good agreement with available experimental data.