Compression mechanisms in α-quartz structures—SiO2 and GeO2

Abstract

Interatomic distances and angles have been measured at pressures to about 25 kbars for the α-quartz forms of SiO2 and GeO2 using time-of-flight powder neutron diffraction. The data show that the compression of SiO2 results solely from a cooperative rotation or tilting of the SiO4 tetrahedra around their shared oxygen corners, with individual tetrahedra remaining relatively rigid. Conversely, the compression of GeO2 results almost solely from distortions of the individual tetrahedra resulting from changes in O-Ge-O angles with cooperative rotations contributing a negligible amount.