Study of the chemical dependence of the effective pair potentials of Co-Ptalloy

Effective pair interaction potentials of Co-Pt alloy have been obtained fro m X-ray diffuse scattering measurements on short-range ordered Co3Pt and Co 65Pt35 Single crystals. The present work presents the evolution of the inte raction energies in the Co-Pt alloy when the Pt concentration varies from 2 5 to 35 at. %. The aim of this work was to provide data in order to improve the computation of the phase diagram by allowing a concentration dependenc e of the effective pair potentials. Different methods have been proposed fo r separating the contributions of local order and first-order displacements from the total diffuse intensity. A comparison of different methods of ana lysis of Co3Pt diffuse-scattering intensity data is reported in the Appendi x of this article; it shows that the second-order displacement terms are al most zero near the transition temperature.