HIGH-PRESSURE CRYSTAL CHEMISTRY AND AMORPHIZATION OF e-QUARTZ

Single-crystal X-ray diffraction experiments on e-quartz at pressures to 15 GPa reveal structural instabilities that result in its gradual transition to an amorphous state. With increasing pressure the average Si-O distance ( ~ 1.61 + 0.01/~) and S i O 4 tetrahedral volume (,,~2.14 ___ 0.02.~ 3) remain constant. Compression of e-quartz results from a dramatic decrease in Si-O-Si angle and corresponding decrease in inter-tetrahedral (i.e., O-O) distances. The onset of amorphization coincides with bending of all Si-O-Si angles to less than 120 ° and severe distortion of SiO4 tetrahedra, as oxygens approach a close-packed configuration.