Local structure and electronic properties of BaTaO2N with perovskite-type structure Original Research Article

First-principles calculation based on density-functional theory in the pseudo-potential approach have been performed for the total energy and crystal structure of BaTaO2N. The calculations indicate a random occupation of the anionic positions by O and N in a cubic structure, in agreement with neutron diffraction measurements and infrared spectra. The local symmetry in the crystal is broken, maintaining a space group Pm3̄m, as used in structure refinement, which represents only the statistically averaged result. The calculations also indicate displacive disordering in the crystal. The average Ta–N distance is smaller (2.003 Å), while the average Ta–O distance becomes larger (2.089 Å). The local relaxation of the atoms has an influence on the electronic structure, especially on the energy gap. BaTaO2N is calculated to be a semiconductor with an energy gap of about 0.5 eV. The upper part of the valence band is dominated by N 2p states, while O 2p states are mainly in the lower part. The conduction band is dominated by Ta 5d states.