The electronic structure of tantalum (oxy)nitrides TaON and Ta3N5

Detailed results of ab initio band structure calcns. for tantalum (oxy)nitrides (TaON and Ta3N5) are reported. The calcns. are performed within the framework of d. functional theory (DFT). We compare results obtained with the mol. dynamics pseudopotential (PP) approach of the Vienna Ab initio Simulation Program (VASP) and the Full Potential Linearized Augmented Plane Waves method (FP-LAPW) using the WIEN97 program. In agreement with neutron diffraction measurements, we show an ordering of the anions in TaON. The calcns. also show that the valence band is composed mainly of the anion 2p orbitals hybridized with Ta 5d states. For TaON the top of the valence band is dominated by N 2p states. The bottom of the conduction band is mainly composed of Ta 5d states. Both TaON and Ta3N5 are semiconductors with calcd. indirect band gaps of resp. 1.8 and 1.1 eV (VASP calcns.) and 2.0 and 1.2 eV (WIEN97 calcns.). Optical diffuse-reflectance spectra show an energy gap of 2.08 eV for Ta3N5. [on SciFinder (R)