Superconductivity of Hf-Ta and Ta-W alloys under pressure

Measurements on ten binary alloys of the body-centered cubic part of the 5d-alloy series Hf-Ta and Ta-W yield a linear relationship between the derivatives of the quantityg both with respect to pressure and to valence electron concentration, whereg is defined byT _c ∝ θ exp (?1/g). This result agrees with observations on alloys of the 4d-series, Zr-Nb and Nb-Mo. It is concluded that for these alloys composed from the central part of the 4d and 5d transition series, the interaction responsible for superconductivity is less subject to complications than for other transition metals and is probably governed by the electronic density of states. Data on the variation of the transition temperature with concentration in Hf-Ta alloys are included.