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

Abstract

The structure of silica glass (SiO2) 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: SiO4-and SiO5-phases. With the increase of density, the structure tends to transform from SiO4-phase into SiO6-phase. At density of 3.582 g/cm 3 , the structure comprises three phases: SiO4-, SiO5-, and SiO6-phases, however, the SiO5-phase is dominant. At higher density (3.994 g/cm 3 ), the structure mainly consists of two main phases: SiO5-and SiO6-phases. In the SiO4phase, the SiO4 units mainly link to each other via corner-sharing bonds. In the SiO5-phase, the SiO5 units link to each other via both corner-and edge-sharing bonds. For SiO6-phase, the SiO6 units can link to each other via corner-, edge-, and face-sharing bonds. The SiO4-, SiO5-, and SiO6-phases form SiO4-SiO5-and SiO6-grains respectively and they are not distributed uniformly in model. This results in the polymorphism in the silica glass at high density.

Characterization of Structural Transition and Heterogeneity under Compression for Liquid Al2O3 Using Molecular Dynamics Simulation

“…These averaged coordination number of Al-O pair is approximately estimated to be 4.3 ± 0.05. To support experimental methods, simulation is also a powerful method to investigate the microstructure of melts, especially at high-temperature and/or pressure conditions [13][14][15][16][17][18][19]. According to the first-principles molecular dynamic (MD) simulations, Verma et al [8] determined that the liquid Al2O3 is more sensitive to the applied compression than the temperature.…”

Atomistic study on tensile fracture of densified silica glass and its dependence on strain rate*

“…[28] The composition and function of different SiO x (x = 4, 5, 6) structures are different in densified silica glass and this variation is often uneven. [29][30][31] Besides, the oxygen hexagonal close-packed (hcp) and facecentered cubic (fcc) clusters were also found in densified silica glass. [32] All these atomic structures are certain to affect the evolution and coalescence of voids.…”