Ordering behaviors of Cd−Mg and Cd−Zn alloys with the h.c.p.-type structure

The structure dependent energy and the ordering energy for an h.c.p.-type binary alloy composed of simple metals are derived from a basis of the method of pseudopotentials. The expressions of the energies are characterized by the long-range and short-range order parameters.The long-range ordering energy is calculated for alloys in the Cd?Mg system. The numerical results reproduce well the fact that the Cd?Mg system has the B19-type ordered phase around the stoichiometric composition of MgCd and the D0₁₉-type ones around Mg₃Cd and MgCd₃. The calculated local ordering energies explain successfully the existence of a short-range order in the Cd?Mg system and also the insolubility between Cd and Zn.