PRESSURE-INDUCED AMORPHIZATION OF BETA-CRISTOBALITE

A constant-pressure molecular-dynamics (MD) study using a three-body potential is employed to study the pressure-induced structural change in beta-cristobalite in the pressure range of 0-23 GPa. Our MD results demonstrate that beta-cristobalite gradually transforms from a crystalline phase to an amorphous phase in the range 11-15 GPa, and abruptly changes to a sixfold-coordinated amorphous silicon structure at 13.5 GPa. Upon release of pressure, the material does not transform back into beta-cristobalite but remains in the amorphous phase with a silicon coordination of nearly six. The behavior of the pressure amorphization of beta-cristobalite is found to be similar to that of pressure amorphization of alpha-quartz. This similarity implies that they may have a similar order-disorder transition mechanism.