# Pressure-induced densification of vitreous silica: insight from elastic properties

## TL;DR

This study uses in situ high-pressure Brillouin scattering to explore how vitreous silica densifies under pressure, revealing reversible structural transformations and residual densification effects related to coordination changes.

## Contribution

It provides new insights into the elastic properties and densification mechanisms of vitreous silica under high pressure, including the correlation with Si coordination and residual densification.

## Key findings

- Elastic properties accurately characterized below 9 GPa.
- Reversible transformation from fourfold to sixfold Si coordination.
- Residual densification can be inferred from pressure cycles.

## Abstract

\textit{In situ} high-pressure Brillouin light scattering experiments along loading-unloading paths are used to investigate the compressibility of vitreous silica. An accurate equation of state is obtained below \SI{9}{GPa} using sound velocities corrected for dispersion. Conversely, huge inelastic effects are observed in the range \SIrange{10}{60}{GPa}, unveiling the reversible transformation from the fourfold-coordinated structure to the sixfold one. We find that the associated density changes fully correlate with the average Si coordination number. Decompression curves from above \SI{20}{GPa} reveal abrupt backward coordination changes around \SIrange{10}{15}{GPa} and significant hysteresis. Further, contrary to common wisdom, the residual densification of recovered silica samples can be figured out from the pressure cycles.