Effects of disorder in Mg 1− xTa xB 2 alloys using the coherent-potential approximation

Abstract

Using the Korringa–Kohn–Rostoker coherent-potential approximation in the atomic-sphere approximation (KKR-ASA CPA) method for taking into account the effects of disorder, Gaspari–Gyorffy formalism for calculating the electron–phonon coupling constant λ, and Allen–Dynes equation for calculating T c, we have studied the variation of T c in Mg 1− x Ta x B 2 alloys as a function of Ta concentration. Our results show that the T c decreases with the addition of Ta for up to 40 at.% and remains essentially zero from 60 to 80 at.% of Ta. We also find TaB 2 to be superconducting, albeit at a lower temperature. Our analysis shows that the variation in T c in Mg 1− x Ta x B 2 is mostly dictated by the changes in the B p density of states associated with the addition of Ta.