Structual Change in Process of Permanent Densification of an Invert Glass : A Molecular Dynamics Simulation

A molecular dynamics simulation was carried out in order to investigate a peculiar permanent densification phenomenon for SiO_2･K_2O･CaO･SrO glasses of an invert composition, i.e., the fraction of SiO_2 lower than 50 mol%. The phenomenon was previously observed by an experiment by high pressure treatment: the densities of permanently densified glasses exhibit a maximun value at 3 GPa (Kawamoto et al., J. Non-Cryst. Solids, 284, 128(2001)). In our simulation, the density profile was qualitatively reproduced: the density after decompression exhibits a maximum at treatment pressure 12 GPa. After decompression, the five-and six-coordinated Si species, which promote a network at high pressure, remain mostly at treatment pressure of 12 GPa, where the density exhibits a maximum