Theoretical Study of Electronic Structure and Superconductivity in Nb1−xB2 Alloys

Using the Korringa-Kohn-Rostoker coherent-potential approximation in the atomic-sphere approximation (KKR-ASA CPA) we have studied the changes in the electronic structure and the superconducting transition temperature Tc in Nb1−xB2 alloys as a function of x. We find that the variation in the electronic structure of Nb1−xB2 alloys as a function of x is consistent with the rigid-band model. However, the variation of Tc, obtained using the Allen-Dynes equation within the Gaspari-Gyorffy formalism to estimate the electronphonon matrix elements, does not follow the expected trend. We associate this disagreement to the use of a constant ωrms in the Allen-Dynes equation over the whole range of vacancy concentration, thereby indicating the importance of lattice dynamical effects in these systems.