Structural Analysis of Amorphous GeO$_2$ under High Pressure Using Reverse Monte Carlo Simulations

TL;DR

This study uses reverse Monte Carlo simulations to analyze how the atomic structure of amorphous GeO₂ changes under high pressure, revealing retention of tetrahedral units up to moderate pressures and a gradual transition to higher coordination states at higher pressures.

Contribution

It provides the first detailed structural analysis of amorphous GeO₂ under high pressure using neutron diffraction data and reverse Monte Carlo simulations.

Findings

Tetrahedral GeO₄ units are retained up to ~4 GPa.

Increase in GeO₅ units observed with pressure.

Gradual transition to GeO₆ units at higher pressures.

Abstract

The structural properties of amorphous GeO$_2$, a prototypical network glass, were investigated under ambient to high pressure using reverse Monte Carlo simulations based on reported structure factors from in situ high-pressure neutron diffraction experiments with isotopic substitution. The results indicate the retention of the topological structure containing predominantly tetrahedral GeO$_4$ units up to ca.~\SI{4}{\giga\pascal} ($\rho/\rho_0 = 1.15$), which is explained by the reduction of cavity volumes. With further application of pressure, an increase in the number of GeO$_5$ units is first observed, which is then followed more gradually by an increase in the number of GeO$_6$ units.