Thermodynamic properties of solid alloys. II. Order-disorder transitions in Mg₃Cd and MgCd₃

For pt.I see ibid., vol.6, p.1039 (1976). A formalism, based on the use of pseudopotentials and the Gibbs-Bogoliubov inequality on the Helmholtz free energy, is presented for the investigation of thermodynamic properties and order-disorder transitions of binary alloys. Application of the method to Mg 3 Cd and MgCd 3 shows that the effect of lattice vibrations can account for about a quarter of the difference in the observed order-disorder transition temperatures of these two alloys. The thermodynamic properties of Mg 3 Cd have been calculated for a wide range of temperatures and the results are in satisfactory agreement with experiment.