Differential strain and residual anisotropy in silica glass

To understand the behavior of SiO2 glass under high pressure and differential stress, we conducted radial x-ray diffraction measurements on SiO2 glass up to 60 GPa, in which x-rays irradiate the sample from a direction perpendicular to the compression axis of a uniaxial apparatus. The differential strain of SiO2 glass, determined from the azimuth angle dependence of the position of the first sharp diffraction peak, was very large especially at pressures below 20 GPa and decreased with increasing pressure. After decompression, a large differential strain, equivalent to about 2 GPa in differential stress, remained in the glass at ambient conditions. We attribute this residual anisotropy to the anisotropic permanent densification, which is caused by the anisotropic change in intermediate-range structure, i.e., the anisotropic reconstruction of the network structure consisting of SiO4 tetrahedra. (C) 2013 AIP Publishing LLC.