Electronic changes induced by vacancies on spectral and elastic properties of titanium carbides and nitrides

Abstract

Abstract Substoichiometric carbides TiC0.49, TiC0.78 and nitrides TiN0.45, TiN0.61 have been synthesized by multiple energy ion implantation of C+ and N+ in polycrystalline titanium. Here, we review theoretical and experimental results concerning the electronic structure of these compounds with various degrees of vacancies. The valence band X-ray photoemission spectra (v-XPS) as well as core level XPS suggest important changes of the electronic structure in comparison to the corresponding stoichiometric compounds. New structures appear near the Fermi level in the experimental v-XPS spectra in agreement with tight-binding-linear-muffin-tin-orbitals (TB-LMTO) calculations of the electronic densities of states (DOS). These structures, absent in stoichiometric compounds, are interpreted as resulting from Ti–Ti bond states between neighbouring titanium atoms through vacancies induced by substoichiometry along the whole range of vacancy concentration. Moreover, these bond modifications explain the experimental changes of Young’s modulus, observed by nanoindentation, in substoichiometric titanium carbides and nitrides.