Shock-induced irreversible transition from α-quartz to CaCl2-like silica

Previous analyses of quartz samples recovered after being submitted to laser shocks of very short duration (nanosecond order) have shown the presence of CaCl2-like silica [T. de Resseguier, P. Berterretche, M. Hallouin, and J. P. Petitet, J. Appl. Phys. 94, 2123 (2003)]. To date, this transition has never been observed under shocks of longer duration (microsecond order) generated by explosives or plate impacts. While this phase is produced from stishovite under static compression at very high pressure (above 50 GPa) and disappears on pressure release, it is observed after low pressure laser shocks (below 5 GPa) and it is quenched to ambient conditions. The origins of these differences are still unclear. This paper presents complementary laser shock experiments involving setups to provide additional information on the influence of various shock parameters. The results suggest a direct transition from α-quartz to CaCl2-type silica following a diffusionless mechanism involving high shear strains. They also show the presence of vitreous silica characterized by an 'organized' ringlike structure, and we propose that this amorphous phase is an intermediate structure between the quartz lattice and grains of the high-pressure phase