Crystallization of amorphous silica under compression

Abstract

The structural phase transformation and crystallization of amorphous silica at 500 K under high pressure are investigated by molecular dynamics simulation. Under compression, there is a structural transformation from tetrahedral- to octahedral-network via SiO5 units. Structural transformation occurs strongly in the 5–15 GPa pressure range and there exist three structural phases corresponding to SiO4, SiO5, and SiO6. Beyond 15 GPa, octahedral-network is dominant. At pressure higher than 20 GPa, octahedral network tends to transform to crystalline phase (stishovite). Mechanism of structural transformation is clarified via coordination-number, bond-angle distributions, bond length distribution, and 3D visualization. The size-distribution of phase regions is also determined in this work.