Local structure and electronic properties of BaTaO2N with perovskite-type structure

First-principles calcn. based on d.-functional theory in the pseudo-potential approach were performed for the total energy and crystal structure of BaTaO2N. The calcns. indicate a random occupation of the anionic positions by O and N in a cubic structure, in agreement with neutron diffraction measurements and IR spectra. The local symmetry in the crystal is broken, maintaining a space group Pm.hivin.3m, as used in structure refinement, which represents only the statistically averaged result. The calcns. also indicate displacive disordering in the crystal. The av. Ta-N distance is smaller (2.003 A), while the av. Ta-O distance becomes larger (2.089 A). The local relaxation of the atoms has an influence on the electronic structure, esp. on the energy gap. BaTaO2N is a semiconductor with an energy gap of .apprx.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.