TITANIUM CARBONITRIDES, TI(C,N) - ELECTRONIC-STRUCTURE AND CHEMICAL BONDING

The structures of the titanium carbonitrides are derived from the sodium chloride structure and do not show long-range order at the non-metal sublattice. To investigate the bonding properties, band structure calculations for three ordered model structures with compositions TiC0.75N0.25, TiC0.5N0.5 and TiC0.25N0.75 using the linear augmented plane-wave (LAPW) method have been performed. For these structures densities of states (DOS), local partial DOS and electron densities have been calculated. The DOS are in fairly good agreement with those previously obtained by the Korringa-Kohn-Rostoker - coherent-potential approximation (KKR-CPA) method where the C and N atoms are assumed to be randomly distributed over the non-metal sublattice. The covalent C-Ti bonds are in general much stronger than the N-Ti bonds and therefore successive replacement of N atoms in TiN by C atoms leads to a strengthening of covalent non-metal-Ti bonds. This is accompanied by a weakening of Ti-Ti bonds and by a decreasing ionicity of the non-metai-Ti bonds.