Electronic structure and stability of low symmetry Ta2O5 polymorphs

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 delta- and beta-Ta2O5 and metastable relative to other recently proposed structures. Its diffraction spectrum and bandgap energy are in good agreement with experimental data. Therefore, the pseudo-hexagonal structure might form in polycrystalline films and affect the switching process of resistive memory devices. Moreover, a neutral oxygen vacancy is found to induce an occupied defect state at 2.5 eV above the top of the valence band, in agreement with X-ray photoelectron spectroscopy results. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim