Electron–phonon coupling constant and critical temperature of binary and ternary superconducting alloys of V, Nb, Mo, and Ta

Abstract

A modified version of the theory of Gaspari and Gyorffy for calculating the electron–phonon coupling constant, λ, for binary substitutional alloys has been used in conjunction with McMillan's expression as modified by Dynes for the superconducting transition temperature, Tc, to obtain λ and Tc for the substitutional alloys NbTa, NbV, VMo, VTa, and TaMo. The theory has been further extended via the Average T-matrix Approximation to calculate λ and Tc for the ternary alloy, NbTaMo, having the same body-centered cubic structure as its components. The calculations of λ are based on self-consistent APW or KRR band structure data for the transition elements V, Nb, Mo, and Ta, obtained by using either Xα or the Hedin–Lundqvist version of the [Formula: see text] exchange approximation to calculate the potentials. The results thus obtained at different concentrations agree favourably with experiments for NbTa, NbV, VMo, and VTa. For TaMo and NbTaMo, for which experimental data on Tc are not yet available, we predict that they are fairly good superconductors.