Experimental Study of the Short Range Order in the PT-V System: Effective Pair Interactions as a Function of the Concentration

Abstract

We present a detailed study of interactions in two alloys, Pt ₃ V and Pt ₈ V, and preliminary results on Pt ₄ V. 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), particulary in Pt ₈ V, where the diffuse intensity maxima do not peak at special points of the fcc lattice. Using inverse Monte Carlo (IMC) simulations, 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 independant. 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 stoechiometry A ₅ B which has never been observed until now.