Understanding the elemental process of viscous flow of silicate liquids from atomistic insights

Silicate liquids possess a network structure composed of corner-sharing SiO4 tetrahedra. The fundamental process of the self-diffusion of network-forming elements remains unclear because of its network structure. This article presents several insights into the diffusion mechanism of network-forming elements by introducing the author’s previous studies with molecular dynamics simulations. Analysis of situation-wise mean square displacement reveals that diffusion via reptation occurs only in basic silicate liquids. Chemical species-wise distinct parts of van Hove’s function indicate that only non-bridging oxygen diffuses via a site-exchange manner in network-forming elements. Recently the author introduced the concept of bond forming/breaking particles. Pair-correlation functions of those particles clarified two individual bond-exchange modes for Si—O bonding. The angular part of the pair-correlation provides an atomistic description of two individual bond-exchange modes. One mode represents the bond exchange in sliding manner, while the other corresponds to the bond exchange in oscillating mode. The pair-correlation functions of bond forming/breaking particles are applicable to quantitative analysis of bond-exchange events in other condensed materials.