New pressure-induced transformations of silica at room temperature

Abstract

SILICA has many polymorphs, and the solid-state transformations between these under pressure have been studied extensively to gain insight into the mechanisms of such high-pressure transitions in general. Most of the transformations of silica polymorphs have been thought to require high temperatures as well as high pressures. Recently, however, a pressure-induced change in silicon coor-dination in silica glass¹ and amorphization of quartz and coesite (a high-pressure phase)² have both been observed at room tem-perature. Here we report two new room-temperature pressure-induced transformations of silica, observed by in situ X-ray diffraction. At pressures above 10 GPa, cristobalite transforms into a new phase, and above 30 GPa a second new phase is formed, both of which are crystalline. Above 60 GPa, however, quartz transforms to poorly crystallized stishovite, probably via an amor-phous state. The new high-pressure polymorphs are probably metastable, and may involve a change in silicon coordination.