High-pressure structural, elastic, and thermodynamic properties of zircon-type HoPO4 and TmPO4

TL;DR

This study combines experimental and computational methods to analyze the structural, elastic, and thermodynamic properties of HoPO4 and TmPO4 under high pressure, revealing their compressibility, stability, and elastic anisotropy.

Contribution

It provides detailed high-pressure data and insights into the stability and elastic behavior of zircon-type HoPO4 and TmPO4, including the causes of structural instability.

Findings

Both compounds are ductile and resist volume compression more than shear deformation.

Elastic anisotropy increases with pressure.

Structural instability is linked to mechanical instabilities and softening of a silent B1u mode.

Abstract

Zircon-type HoPO4 and TmPO4 have been studied by single-crystal x-ray diffraction and ab initio calculations. We report information on the influence of pressure on the crystal structure, and on the elastic and thermodynamic properties. The equation of state for both compounds is accurately determined. We have also obtained information on the polyhedral compressibility which is used to explain the anisotropic axial compressibility and the bulk compressibility. Both compounds are ductile and more resistive to volume compression than to shear deformation at all pressures. Furthermore, the elastic anisotropy is enhanced upon compression. Finally, the calculations indicate that the possible causes that make unstable the zircon structure are mechanical instabilities and the softening of a silent B1u mode.