Possible Orthorhombic Phase of Ta$_2$O$_5$ under High Pressures

TL;DR

This study predicts a new orthorhombic phase of Ta$_2$O$_5$ under high pressure using advanced computational methods, revealing its stability, electronic properties, and the importance of nuclear quantum effects.

Contribution

The paper introduces a previously unknown orthorhombic phase of Ta$_2$O$_5$ stable at high pressures, characterized by high coordination and wide bandgap, using DFT and GW calculations.

Findings

Y-Ta$_2$O$_5$ is most stable between 70 GPa and 200 GPa.

Y-Ta$_2$O$_5$ has the highest known Ta-O coordination.

Nuclear quantum effects significantly affect phase stability.

Abstract

A potential orthorhombic phase of Ta$_2$O$_5$, designated as Y-Ta$_2$O$_5$, is predicted under high-pressure conditions through density functional theory (DFT) calculations combined with structural search algorithms. This phase, consisting of four formula units per unit cell ($Z = 4$), exhibits the highest known Ta-O coordination numbers. Y-Ta$_2$O$_5$ is found to be the most energetically favorable form of Ta$_2$O$_5$ in the pressure range of approximately 70 GPa to at least 200 GPa. Both standard DFT-GGA and higher-accuracy GW calculations reveal that Y-Ta$_2$O$_5$ is a wide bandgap semiconductor with a direct bandgap. Additionally, nuclear quantum effects (NQEs) introduce nontrivial corrections to external pressure at fixed volumes, underscoring their significance in high-pressure phase stability analyses.