Theory of Systematic Absence of NaCl-Type ( β -Sn–Type) High Pressure Phases in Covalent (Ionic) Semiconductors

Recent high pressure x-ray experiments show that, contrary to traditional expectations, the NaCl structure is not present in covalent semiconductors, and the diatomic β-Sn structure is absent in all compound semiconductors. We explain these systematic absences in terms of dynamical phonon instabilities of the NaCl and β-Sn crystal structures. Covalent materials in the NaCl structure become dynamically unstable with respect to the transverse acoustic TA[001] phonon, while ionic compounds in the β-Sn structure exhibit phonon instabilities in the longitudinal optical LO[00ξ] branch. The latter lead to predicted new high pressure phases of octet semiconductors.