Equilibrium atomic compositions of MoxRe1−x(0 0 1) and MoxW1−x(0 0 1) disordered alloys

The cluster expansion model for the internal energy in terms of effective cluster interactions is employed to study the thermodynamic properties of two semi-infinite binary alloy systems: MoRe and MoW. A realistic tight-binding Hamiltonian is used with configurational averages computed by the direct method. This framework is applied to calculate the equilibrium atomic compositions of the (0 0 1) surface of MoxRe1−x and MoxW1−x systems for different bulk concentrations. In all cases it is found that the Mo component segregates strongly to the surface plane, followed by a Mo depletion in the second plane. The major role played in the segregation process by the relevant quantities, namely, point energies and pair interactions, is emphasized. These results are in good agreement with available experimental data.