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

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.

30 Pages, 4 Figures, 2 Tables