Monte Carlo calculations of thermodynamic properties of alloys in the case of the surrounded atom model

Abstract

Monte Carlo calculations are carried out to give exact values of some thermodynamic properties of alloys. The calculations are performed within the framework of the surrounded atom model the main assumptions of which are: quasilattice structure of the alloy, nearest neighbour interactions, description of the configuration in terms of “surrounded atoms”. The results are then compared with those obtained using current approximations: the Bragg-Williams treatment and the quasichemical treatment. This work enables us to generalize the previous conclusions drawn in the study of the regular solution model. In every case, whatever the sign of the interactions (ordering or clustering tendency) Monte Carlo calculations yield a local order that both approximations fail to reproduce. In order to compare the calculations with some experimental data, Cowley's short range order parameter α 1, is calculated by Monte Carlo and by the approximate methods (the parameters of the surrounded atom model are derived from thermodynamic data). The Monte Carlo values compare better than the quasichemical ones with the data obtained by X-ray or neutron diffraction in three actual systems.