Anisotropy in the structure of pressure-induced disordered solids

Abstract
Molecular dynamics calculations revealed that a pressure-induced ‘‘amorphized’’ solid is disordered and anisotropic but not structurally related to an isotropic quenched melt. The results explain the anomalous elastic behavior observed via Brillouin scattering on α-quartz [L. E. McNeil and M. Grimsditch, Phys. Rev. Lett. 68, 83 (1991)]. The reversal in frequency shifts for sound propagation in the perpendicular and parallel directions is due to the unequal densification in the a and c directions. The helical chains are found to recover upon depressurizing. Anisotropy of pressure amorphized solids is thus a general property, and pressure-induced amorphization is not related to melting.