Electronic structure of stoichiometric and off-stoichiometricTaCx

Abstract
We have determined the electronic structure of stoichiometric and substoichiometric TaC by means of the relativistic Korringa-Kohn-Rostoker Green’s-function method. The introduction of vacancies was treated within the coherent-potential approximation. We find that the main difference between the ordered and disordered compound is a charge transfer from the nonmetal to the metal atom. Additional vacancy states (-3.0 eV below the Fermi energy) play a minor role. We calculate x-ray photoemission spectroscopy (XPS) intensities for both stoichiometric and substoichiometric cases and find (unlike previous calculations) excellent agreement with the XPS data. We also compare our results with the measured linear specific-heat coefficient and find that the sharp drop seen in this quantity with increasing vacancy concentration cannot be explained by our results.