Electronic structure of cubic Hf x Ta1–x C y carbides from X-ray spectroscopy studies and cluster self-consistent calculations

Abstract: X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) methods were employed in the present work to investigate the electronic structure of almost stoichiometric cubic (NaCl structure) Hf x Ta1–x C y carbides. The XPS valence-band and core-level spectra, the XES bands reflecting energy distributions of mainly the Ta 5d- and C 2p-like states as well as the XAS Ta LIII edges (unoccupied Ta d-like states) were derived and compared on a common energy scale for cubic HfC0.95, Hf0.5Ta0.5C0.94 and TaC0.98 compounds. To investigate the influence of substitution of tantalum atoms for hafnium atoms in the Hf x Ta1–x C y carbides, cluster self-consistent calculations of total and partial densities of states were carried out with the FEFF8 code for HfC, Hf0.5Ta0.5C and TaC compounds possessing the NaCl-type structure. In the present work a rather good agreement of the experimental and theoretical results for the electronic structure of the Hf x Ta1−x C y system under study was obtained. The results indicate that a strong hybridization of the Hf(Ta) 5d- and C 2p-like states is characteristic for the Hf x Ta1−x C y carbides. It has been established that, substitution of hafnium atoms by tantalum atoms in the Hf x Ta1−x C y system reveals increasing the half-width of the XES C Kα band. When going from HfC0.95 to TaC0.98 through the carbide of intermediate composition, the main maximum of the XPS valence-band spectrum shifts in the direction opposite to the position of the Fermi level. In the above sequence of compounds the asymmetry index of the C Kα bands decreases significantly. [Copyright &y& Elsevier]