Stability of high-pressure phases in II-VI semiconductors by a density functional lattice dynamics approach

Abstract

Stability of the rocksalt structure with respect to the high-pressure $Cmcm$ structure was investigated for several II-VI semiconductors (ZnS, ZnSe, CdS, and CdSe). The lattice dynamics calculations reveal that the rocksalt structure is unstable with respect to the transversal acoustic mode at the Brillouin zone boundary. The phase transition is of the second order and is associated with cell doubling in the high-pressure $Cmcm$ phase with frozen deformation. The present calculation gives the transition pressure more accurately than the classical method, which uses the common tangent. Since the volume change at the transition is very small or zero in all studied crystals, transitions were estimated from the pressure at which the frequency of the zone boundary transversal acoustic mode goes to zero. The observed pressures of the phase transitions in structural measurements were reproduced more accurately than in previous calculations and the difference between observed and calculated transition pressure is of the order of 1% to 8%.