Pressure induced phase transformations in silica

Silica, SiO₂, is one of the most widely studied substance because of its complex and unusual properties. We have used a recently developed 2-body interaction force field to study the structural phase transformations in silica under various pressure loading conditions. The specific transformations we studied are the α-quartz to stishovite, coesite to stishovite and fused glass to a dominantly six-coordinated dense glassy phase. Molecular dynamics simulations are performed under constant loading rates ranging from 0.1 GPa/ps to 1.0 GPa/ps, with final pressures up to 100 GPa and at temperatures of 300, 500, and 700 K. We observe the crystal to crystal transformations to occur reconstructively, whereas it occurs in a smooth and displacive manner from glass to a stishovite-like phase confirming earlier conjectures. We studied the dependence of transition pressure on the loading rate and the temperature to elucidate the shock loading experiments. We also studied the unloading behavior of each transformation to assess the hysteresis effect.