Transformation Pathways of Silica under High Pressure

TL;DR

This paper investigates how silica densifies under high pressure, revealing a two-stage mechanism involving anion packing and cation redistribution, supported by simulations and calculations that clarify a previously ambiguous metastable phase.

Contribution

It uncovers the detailed two-stage densification process of silica under pressure and conclusively determines the structure of a metastable phase observed experimentally.

Findings

Densification occurs via a two-stage mechanism.

A metastable phase forms during densification.

Simulations reveal the structure of the metastable phase.

Abstract

Concurrent molecular dynamics simulations and ab initio calculations show that densification of silica under pressure follows a ubiquitous two-stage mechanism. First, anions form a close-packed sub-lattice, governed by the strong repulsion between them. Next, cations redistribute onto the interstices. In cristobalite silica, the first stage is manifest by the formation of a metastable phase, which was observed experimentally a decade ago, but never indexed due to ambiguous diffraction patterns. Our simulations conclusively reveal its structure and its role in the densification of silica.