SURFACE SEGREGATION OF PDRH, PDNI AND PDCO ALLOYS

Surface segregation in paramagnetic Pd-Rh, Pd-Co and Pd-Ni alloys has been considered in terms of the Bethe-Peierls approximation of the coherent potential and the continued fraction method. A microscopic model calculation is performed by taking into account the different bandwidths of the alloy components and the surface potentials, providing the charge conservation condition at the surface. Analytical estimations of segregation trends have been made for the case of an alloy with close centers of the valence bands. The numerical calculations show that the Pd segregation in all three alloys studied is in agreement with the Miedema theory and with experimental results for Pd-Ni alloys. Also, X-ray photoemission (XPS) surface core-level energy shifts are considered in the light of our approach.