Vacancy-induced fine structure in the K edges of sub-stoichiometric titanium and vanadium nitrides

Abstract

Structure near the X-ray absorption K-edge of a wide range of sub-stoichiometric titanium and vanadium nitrides has been examined. Oxygen-free 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 characterized by X-ray diffraction. A peak in intensity at the onset of the Ti K-edge develops with increasing vacancy concentration and can unambiguously be attributed to vacancy-induced p-like states. Although the p-like densities of unoccupied states at the V K-edge are also modified by the introduction of vacancies, there is no equivalent appearance of a vacancy peak. This confirms the theoretical predictions of first-principles KKR-CPA band structure calculations. These measurements also demonstrate that no quadrupole transitions need to be invoked to interpret the spectra and that for such metallic compounds agreement with calculated ground state properties is good. Comparison with data taken at the K-edge of three ZrCN compounds (isoelectronic with TiCN) indicate that hybridization between the non-metal 2p states and the Zr 5p states is greatly reduced compared to that of the Ti or V 4p states.