A combined XAS and XRD Study of the High-Pressure Behaviour of GaAsO4 Berlinite

TL;DR

This study combines XAS and XRD techniques to investigate high-pressure structural changes in GaAsO4, revealing coordination transformations, reversible and irreversible phase transitions, and detailed local atomic environment evolution.

Contribution

It provides a comprehensive analysis of GaAsO4's high-pressure behavior using combined spectroscopic and diffraction methods, highlighting coordination changes and phase transition mechanisms.

Findings

Coordination changes from four- to six-fold for both cations.

Reversible transition around 8 GPa to a high-pressure crystalline form.

Irreversible transition at higher pressures to a disordered phase.

Abstract

Combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) experiments have been carried out on GaAsO4 (berlinite structure) at high pressure and room temperature. XAS measurements indicate four-fold to six-fold coordination changes for both cations. The two local coordination transformations occur at different rates but appear to be coupled. A reversible transition to a high pressure crystalline form occurs around 8 GPa. At a pressure of about 12 GPa, the system mainly consists of octahedral gallium atoms and a mixture of arsenic in four-fold and six-fold coordinations. A second transition to a highly disordered material with both cations in six-fold coordination occurs at higher pressures and is irreversible.