High-pressure structural and elastic properties of Tl2O3

TL;DR

This study combines experimental and theoretical methods to investigate the high-pressure structural and elastic properties of Tl2O3, revealing pressure-induced amorphization and potential mechanical instability of its cubic structure.

Contribution

It provides new experimental data on Tl2O3's behavior under pressure and theoretical insights into the mechanisms behind amorphization and phase stability.

Findings

Tl2O3 remains cubic up to 22 GPa

Amorphization occurs at 25.2 GPa after initial cubic phase

Theoretical predictions suggest mechanical instability causes amorphization

Abstract

The structural properties of Thallium (III) oxide (Tl2O3) have been studied both experimentally and theoretically under compression at room temperature. X-ray powder diffraction measurements up to 37.7 GPa have been complemented with ab initio total-energy calculations. The equation of state of Tl2O3 has been determined and compared to related compounds. It has been found experimentally that Tl2O3 remains in its initial cubic bixbyite-type structure up to 22.0 GPa. At this pressure, the onset of amorphization is observed, being the sample fully amorphous at 25.2 GPa. The sample retains the amorphous state after pressure release. To understand the pressure-induced amorphization process, we have studied theoretically the possible high-pressure phases of Tl2O3. Although a phase transition is predicted at 5.8 GPa to the orthorhombic Rh2O3-II-type structure and at 24.2 GPa to the orthorhombic a-Gd2S3-type structure, neither of these phases were observed experimentally, probably due to the hindrance of the pressure-driven phase transitions at room temperature. The theoretical study of the elastic behavior of the cubic bixbyite-type structure at high-pressure shows that amorphization above 22 GPa at room temperature might be caused by the mechanical instability of the cubic bixbyite-type structure which is theoretically predicted above 23.5 GPa.