Electronic properties of cubic TaCxN1-x: A comparative study using self-consistent cluster and ab initio band-structure calculations and X-ray spectroscopy

To investigate the influence of substitution of carbon atoms for nitrogen atoms in the cubic TaCxN1-x carbonitrides, total and partial densities of states were calculated for TaC, TaC0.5N0.5 and TaN compounds (NaCl structure) using the self-consistent cluster (with the FEFF8 code) and ab initio band-structure augmented plane wave + local orbitals (APW + LO) methods. In the present work a rather good agreement of the theoretical FEFF8 and APW + LO data for electronic properties of the TaCxN1-x system under consideration was obtained. The results indicate that a strong hybridization of the Ta 5d- and C(N) 2p-like states is characteristic for the valence band of the TaCxN1-x carbonitrides. When going from TaC to TaN through the TaC0.5N0.5 carbonitride, the main maxima of curves representing total and partial Ta 5d densities of states shift in the direction opposite to the position of the Fermi level. In the above sequence of compounds, an increase of occupation of the near-Fermi sub-band formed by contributions of Ta 5d(t2g) states has been detected. The theoretical FEFF8 and APW + LO results for the electronic structure of the TaCxN1-x carbonitrides were found to be in excellent agreement with the experimental data derived in the present work employing X-ray photoelectron, emission and absorption spectroscopy methods for cubic TaC0.98, TaC0.52N0.49 and TaN0.97 compounds