Impact of pressure on structure and properties of hot-compressed Na2O-Al2O3-SiO2 glass by molecular dynamics simulations

We conduct systematic studies to investigate the impact of pressure on structure and properties of Na2O-Al2O3-SiO2 glass system using molecular dynamics simulations. Glass compositions range from peralkaline, to charge-balancing, to peraluminous. Hot-compression operation is applied to as-prepared glasses with pressure up to 4 GPa. Several key learnings are obtained from the study: (a) Density and elastic moduli increase with increasing Al/Na ratio (R-Al/Na) and pressure, which are mainly driven by average internetwork bond angle reduction and void size reduction upon compression. (b) Population of three bonded oxygen (TBO) show some presence in the peralkaline composition space, while gain significantly in the peraluminous regime. Pressure essentially encourages conversion of bridging oxygen to nonbridging and three bonded oxygens. Local nearest neighbor environment of TBO is predominately Al atoms rather than Si atoms regardless of R-Al/Na and applied pressure. (c) Analysis of first sharp diffraction peak (FSDP) from neutron scattering suggests that medium-range structure is compacted and small size rings are noticeably distorted over the hot-compression process. (d) Ring size distribution analysis shows that pressure has a more pronounced effect on altering medium-range structure for peralkaline glasses as compared to peraluminous glasses.