Topology of SiO_x-units and glassy network of magnesium silicate glass under densification: correlation between radial distribution function and bond angle distribution

Topology of SiO_x units and glassy network of magnesium silicate glass at different pressures are investigated by molecular dynamics simulation to clarify its microstructure under compression. Results show that SiO_x-topology and glassy network structure are significantly dependent on pressure. At ambient pressure, the –Si–O– glassy network in Mg₂SiO₄ glass is split into subnets/clusters. Under compression, the small subnets tend to merge each other forming larger ones. The decrease of Si–O–Si bond angle under compression that accompanies a formation of edge- and face-sharing bonds between SiO_x units results in the first peak splitting of Si–Si PRDF at high pressure. In particular, the investigation also reveals a tight correlation between PRDFs (Si–Si, Mg–Mg, Si–Mg, O–O) and BADs (Si–O–Si, Mg–O–Mg, Mg–O–Si, O–T–O (T = Si, Mg)), respectively. The spatial distribution of corner-, edge- and face-sharing bonds is not uniform but forming subnets/clusters. The clusters of face-sharing bonds form rigid particles embedding into mixture clusters of corner- and edge-sharing bonds. Size distribution of subnets/clusters (SiO_x-cluster as well as clusters of corner-, edge- and face-sharing bonds) under compression also has been investigated to clarify the intermediate range order. The characteristic change of PRDFs under compression in the relationship with microstructural change and the mechanism of magnesium ions incorporation into –Si–O– network is also discussed in detail. (paper)