VACANCY-INDUCED FINE-STRUCTURE IN THE K-EDGES OF SUB-STOICHIOMETRIC TITANIUM AND VANADIUM NITRIDES

Structure near the X-ray absorption K-edge of a wide range of sub-stoi chiometric titanium and vanadium nitrides has been examined. Oxygen-fr ee TiNx (0.53 < x < 1) and VNx (0.72 < x < 1) were prepared from bulk high purity metal plates heated in a nitrogen atmosphere and character ized by X-ray diffraction. A peak in intensity at the onset of the Ti K-edge develops with increasing vacancy concentration and can unambigu ously be attributed to vacancy-induced p-like states. Although the p-l ike densities of unoccupied states at the V K-edge are also modified b y the introduction of vacancies, there is no equivalent appearance of a vacancy peak. This confirms the theoretical predictions of first-pri nciples KKR-CPA band structure calculations. These measurements also d emonstrate that no quadrupole transitions need to be invoked to interp ret the spectra and that for such metallic compounds agreement with ca lculated ground state properties is good. Comparison with data taken a t the K-edge of three ZrCN compounds (isoelectronic with TiCN) indicat e that hybridization between the non-metal 2p states and the Zr 5p sta tes is greatly reduced compared to that of the Ti or V 4p states.