Electronic structure and charge state of atoms of cubic and hexagonal tantalum carbides

The electronic structure and charge states of atoms of cubic and hexagonal tantalum carbides have been studied by X-ray photoelectron (XPS) and X-ray absorption (XAS) spectroscopy. The XPS spectra of both valence and core-level electrons as well as the TaL _III XAS spectra of TaC_x have been obtained over the range 0.36≤x≤0.98. In all the tantalum carbides studied charge transfer takes place from Ta to C atoms. The shifts of the Ta 4f core levels and the midpoints of the TaL_III absorption edges indicates that the effective positive charge of the Ta atoms decreases in the row TaC_0.98»TaC_0.36. In that sequence of compounds the main peak of the XPS valence band spectra shifts toward the Fermi level by about 0.85 eV.