Concentration variation of the effective pair interactions measured on the Pt-V system. Evaluation of the gamma expansion method

Abstract

We present a detailed study of interactions in two alloys, Pt 3V and Pt 8V, and preliminary results on Pt 4V. In situ neutron scattering experiments were performed in order to measure the short range order parameters in the disordered phase for the two concentrations. We will show the drastic effect of the concentration on the short range order (SRO), particularly in Pt 8V, where the diffuse intensity maxima do not peak at special points of the fcc lattice. Using inverse Monte Carlo (IMC) simulations and the gamma expansion method (GEM), two sets of effective pair interactions (EPI) were deduced from the experimental SRO parameters within the Ising model. Surprisingly, despite quite different SRO patterns, the EPI seem nearly concentration independent. We will show, using MC simulation, that the two very different diffuse intensity maps are well reproduced with the same interaction set. The concentration independence of the EPI allowed us to describe also properties of the ordered states and more generally the whole phase diagram. In particular, we predict the existence, at very low temperature, of a new phase of stoichiometry A 5B which has never been observed until now.