Theoretical study of structural and electronic properties of β-Ta2O5 and δ-Ta2O5 -: art. no. 165202

Using density functional theory within the local density approximation (LDA) and generalized gradient approximation (GGA), we discuss the relative stability of the orthorhombic (or the beta) phase and the hexagonal (or the delta) phase of tantalum pentoxide. We find that, both LDA and GGA pseudopotential calculations favor the delta phase, whereas spin-orbit all-electron calculations favor the beta(delta) phase within the LDA (GGA); however, the all-electron energy differences are too small to be significant. The spin-orbit coupling has a significant effect on the band gaps and the band gap is indirect (direct) in the delta(beta) phase. The chemical bonding between Ta and oxygen ions is of a mixed type (mainly ionic but partly covalent).