The correlation between coordination and bond angle distribution in network-forming liquids

The structure and diffusion in SiO2 and Al2O3 liquids under pressure have been studied by molecular dynamics simulation. We show that although different states of considered liquids differ significantly in the number of TOx units and OTy linkages (T = Si, Al; x = 4, 5, 6; y = 2, 3, 4), their partial bond angle distributions (BAD) are identical. Furthermore, the total BADs are directly related to the partial BADs and coordination distribution. This result supports a technique to determine the fraction of TOx and OTy from the experimental bond angle distribution. The simulation also reveals the anomalous behavior of diffusion in silica liquid caused by the change in diffusion mechanisms occurring in low- and high-density models. The diffusion in alumina liquid also results from a similar mechanism like the one for high-density sample of silica liquid.