The crystal structure of IV-VI compounds. II. A microscopic model for cubic/rhombohedral materials

For pt.I see ibid., vol.13, no.26, p.4855 (1980). A semi-empirical theory is developed for the cubic to rhombohedral phase transition in A N B 10-N compounds, based on the heats of formation and pseudopotential band-structure parameters. Calculations of the rhombohedral shear angle and the internal sublattice displacement in the rhombohedral phase of GeTe, SnTe as well as the group V materials As, Sb and Bi are in good agreement with experiment. A mean-field theory is employed to calculate the phase transition temperature T c in the IV-VI materials, and the pressure coefficient dT c /dp.