Elementary mechanisms governing the dynamics of silica

TL;DR

This study provides a detailed atomistic understanding of silica glass dynamics at low temperatures by analyzing thousands of activated events, revealing collective processes and the roles of dangling bonds in diffusion.

Contribution

It introduces a comprehensive analysis of atomistic mechanisms in silica, highlighting the collective nature of activated processes and the equivalence of silicon and oxygen diffusivities.

Findings

Activated events involve 10 to hundreds of atoms.

Diffusion occurs via creation, annihilation, and movement of dangling bonds.

Silicon and oxygen have similar diffusivities.

Abstract

A full understanding of glasses requires an accurate atomistic picture of the complex activated processes that constitute the low-temperature dynamics of these materials. To this end, we generate over five thousand activated events in silica glass, using the activation-relaxation technique; these atomistic mechanisms are analysed and classified according to their activation energies, their topological properties and their spatial extend. We find that these are collective processes, involving ten to hundreds of atoms with a continuous range of activation energies; that diffusion and relaxation occurs through the creation, annihilation and motion of single dangling bonds; and that silicon and oxygen have essentially the same diffusivity.