THE BEHAVIOR OF ALPHA-QUARTZ AND PRESSURE-INDUCED SIO2 GLASS UNDER PRESSURE - A MOLECULAR DYNAMICAL STUDY

We have carried out extensive molecular dynamical calculations on a-qu artz and pressure-induced glass and have related these to the experime ntal observations under static and shock pressure loading. In the crys talline quartz, densification and amorphization take place sharply aro und 20 GPa and are related to the changes in the Si coordination. The pressure-induced glass is considerably less compressible than the fuse d silica, showing a gradual change in the Si coordination, and is unli ke the glass studied earlier by Tse, Klug and Le Page. However even th is glass shows a densification, similar to that of quartz as well as f used silica. Retrieval of the four-coordinated state, in both cases, r equires annealing at high temperatures. Just before amorphization of a lpha-quartz, 0 atoms are still far from the recently proposed BCC pack ing.