Calculation of thermodynamic quantities of metals and alloys by the statistical moment method

The thermodynamic properties of metals and alloys are studied using the mom ent method in the statistical dynamics, which allows us to take into accoun t the anharmonicity of thermal lattice vibrations and size mismatch of cons tituent atoms, going beyond the quasi-harmonic approximation. Within the fo urth-order moment approximation, the free energy and equilibrium lattice sp acing of the binary alloys are given explicitly in terms of the effective p air potentials and the second- and fourth-order vibrational constants. The long-range order (LRO) parameter eta and order-disorder transition temperat ures (ODTs) T-c of binary alloys are obtained by solving the explicit trans cendental equations. The numerical calculations of thermodynamic quantities for Cu3Au and beta -CuZn alloys show that the inclusion of the anharmonici ty of lattice vibration plays an essentially important role in determining the phase stabilities of metals and alloys.