Influence of interstitial impurities (C, N) on electronic structure and size factor of niobium-based solid solutions

The self-consistent electronic band structure calculations for niobium-based solid solutions of carbon and nitrogen are performed using the Linear Muffin-Tin Orbitals method in atomic sphere approximation. The Nb-C and Nb-N interactions, which result in impurity-induced low-energy structures in the densities of states, are analysed by means of the partial-wave decomposition. The interstitial-solvent atom electronic interactions are found to be essentially short-ranged and limited by the six neighbours nearest to the octahedral interstice. The change in the position of Fermi level in the metal d-bands, which occurs on alloying niobium by carbon and nitrogen, is discussed. The monotonous decreasing of the electron densities of states at the Fermi level on increasing carbon and nitrogen concentration was found. In the frame of the first principles' method, the size factors of niobium-based solid solutions of carbon and nitrogen are calculated. It is shown that a satisfactory agreement with the experimental results has been achieved.