Recent high pressure x-ray experiments show that, contrary to traditional expectations, the NaCl structure is not present in covalent semiconductors, and the diatomic $\beta -\mathrm{Sn}$ structure is absent in all compound semiconductors. We explain these systematic absences in terms of dynamical phonon instabilities of the NaCl and $\beta -\mathrm{Sn}$ 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 $\beta -\mathrm{Sn}$ structure exhibit phonon instabilities in the longitudinal optical $\mathrm{LO}\left[00\xi \right]$ branch. The latter lead to predicted new high pressure phases of octet semiconductors.

• Received 23 July 1998

DOI:https://doi.org/10.1103/PhysRevLett.82.767