First-principles total energy calculations were used to characterize O vacancy defects in Ta2O5. A simplified version of the crystalline orthorhombic phase of Ta2O5 was used here. The results indicated that O vacancies in Ta2O5 could be broadly classified based upon their location in the lattice. One type of vacancy that occupies the so-called in-plane sites displays deep or mid-gap occupied states and shallow unoccupied states, while a second type occupying so-called cap sites resulted in shallow occupied states. For a wide range of Fermi levels or chemical potentials, the neutral and +2 charged states of the in-plane type vacancy and the +2 charge state of the cap type vacancy were found to be most stable.

First-Principles Study of Oxygen Vacancy Defects in Tantalum Pentoxide. R.Ramprasad: Journal of Applied Physics, 2003, 94[9], 5609-12