First-Principles Study of Oxygen Vacancy and Hydrogen Impurity Effects in the Pseudo-Hexagonal Ta₂O₅

Abstract

The structures and electronic properties of Ta2O5 polymorphs were calculated using density-functional theory employing the generalized gradient approximation with on-site Coulomb corrections. Using this approach, a pseudo-hexagonal structure was found to be a stable polymorph of Ta2O5 over the 14δ' type="#_x0000_t75"> - and 14β' type="#_x0000_t75"> -Ta2O5 and is proposed as a new candidate structure which might be formed during the resistive switching process in random access memory devices. Its diffraction spectrum is shown to successfully match the recently indexed experimental structure and its band-gap energy is also in good agreement with available experimental data. A neutral oxygen vacancy is shown to induce an occupied defect state at 2.5 eV above the top of the valence band, as also found by x-ray photoelectron spectroscopy spectrum measurement. Furthermore, the effects of the hydrogen impurity on the electronic structures were investigated.

Tantalum Pentoxide: From Crystal Structures to Applications in Water Splitting

“…However, both the βphase and δ-phase exhibit some instability and require large supercells for accurate structure optimization. The band gaps of 2.65 170 1.06, 161 1.1 100 3.24 171 3.9, 167 β-Ta 2 O 5 and δ-Ta 2 O 5 calculated using GGA are 0.2 and 1.06 eV, respectively, which underestimate the experimentally reported band gap of around 3.9 eV. This underestimation can be addressed using U-correction methods.…”