Enhanced plasticity of silica glass at high pressure

We have measured shear flow and residual structural anisotropy of SiO2 glass uniaxially compressed in a diamond-anvil cell at room temperature with in situ optical-microscope and ex situ x-ray diffraction techniques, respectively. Large shear flow began at 8-10 GPa and continued at least up to 20 GPa, where the macroscopic differential strain reached 70%. Recovered samples after shear flow were in the fully densified state and showed a large microscopic differential strain of 3% only in the intermediate-range network structure. These phenomena may be attributable to the changes in the Si-O bond covalency and the Si-O-Si bond angle with pressure and stresses.