Effects of disorder in Mg1−xTaxB2 alloys using the coherent-potential approximation

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 Tc, we have studied the variation of Tc in Mg1−xTaxB2 alloys as a function of Ta concentration. Our results show that the Tc 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 TaB2 to be superconducting, albeit at a lower temperature. Our analysis shows that the variation in Tc in Mg1−xTaxB2 is mostly dictated by the changes in the B p density of states associated with the addition of Ta.