Molecular dynamics simulation of shock-induced structural change and permanent densification of silica glass: The effect of initial density

This work investigates the Hugoniot relation, structural change and permanent densification of initial densified silica glass under shock compression-release by atomistic simulations. The Hugoniot results show a good agreement with the experimental data. Moreover, the shock velocity and shock pressure are found to increase with the initial density of sample, and the pressure gap between different samples will be increased with the impact velocity. The microstructural analysis shows the decrease of Si–Si, O–O nearest-neighbor distance, Si–O–Si bond angle and the increase of 5-fold, 6-fold Si atoms during the plastic region. Also, those microscopic changes will get smaller with the increase of initial densification below 14 GPa, and all the samples undergo similar structural changes after complete densification identified by the splitting of Si–Si peak, the new O–O peak and 6-fold Si atoms. Considering the release from the shock pressure above 14 GPa, the initial incomplete densified samples can reach the maximum densification of 2.56 g/cm³, where Si–O–Si bond angle decreases, and 11% 5-fold Si appears. It is found that the shock release cannot make the sample obtain the maximum densification of 20%. Besides, HCP or FCC O atoms are observed in all samples when the shock pressure is over 30 GPa, indicating the crystallization tendency of silica glass. The initial densification seems to promote the transformation to stishovite phase.