Structure of a New High Pressure Phase inα-Quartz Determined by Molecular Dynamics Studies

Kingma et al. have recently reported the diffraction evidence of a new phase transition in $\alpha$-quartz at 21 GPa. We use molecular dynamical calculations to show this phase to be the precursor on the way to amorphization. The powder x-ray patterns generated from the simulated structure show the emergence of superlattice peaks at ≅20 GPa. These predicted diffraction patterns are in excellent agreement with the experimental results and are indicative of a tripling of the unit cell in the a-b (basal) plane of $\alpha$-quartz. In the pressure amorphized phase the calculated structure factor, $S\left(Q\right)\mathrm{}$, is also in excellent agreement with the experimental results of Meade et al.