The structural transition under densification and the relationship between structure and density of silica glass

The structure of silica glass (SiO 2 ) at different densities and at temperatures of 500 K is investigated by molecular dynamics simulation. Results reveal that at density of 3.317 g/cm 3 , the structure of silica glass mainly comprises two phases: SiO 4 - and SiO 5 -phases. With the increase of density, the structure tends to transform from SiO 4 -phase into SiO 6 -phase. At density of 3.582 g/cm 3 , the structure comprises three phases: SiO 4 - , SiO 5 -, and SiO 6 -phases, however, the SiO 5 - phase is dominant. At higher density (3.994 g/cm 3 ), the structure mainly consists of two main phases: SiO 5 - and SiO 6 -phases. In the SiO 4 -phase, the SiO 4 units mainly link to each other via corner-sharing bonds. In the SiO 5 -phase, the SiO 5 units link to each other via both corner- and edge-sharing bonds. For SiO 6 -phase, the SiO 6 units can link to each other via corner-, edge-, and face-sharing bonds. The SiO 4 -, SiO 5 -, and SiO 6 -phases form SiO 4 - SiO 5 - and SiO 6 -grains respectively and they are not distributed uniformly in model. This results in the polymorphism in the silica glass at high density. Graphical abstract