Complementary ab initio and X-ray nano-diffraction study of Ta2O5
  Numerous different crystal structures of Ta2O5 are reported in literature. Although experimentally and computationally obtained lattice parameters and mechanical properties are in excellent agreement there is a pronounced deviation when it comes to electronic structures of Ta2O5. Based on ab initio studies and nano-beam X-ray diffraction of sputtered Ta2O5 thin films, we introduce an orthorhombic basic structure with a = 0.6425, b = 0.3769, and c = 0.7706 nm, which is stabilized by flipping of an oxygen atom in neighboring c-planes. The calculated energy of formation is with -3.209 eV/atom almost as low as -3.259 eV/atom for the well-known Stephenson superstructure. We propose the new structure based on the fact that it allows for a good description of orthorhombic Ta2O5 even with a small and simple unit cell, which is especially advantageous for computational studies. 
R. Hollerweger, D. Holec, J. Paulitsch, M. Bartosik, R. Daniel, R.   Rachbauer, P. Polcik, J. Keckes, C. Krywka, P. H. Mayrhofer
cond-mat.mtrl-sci