Effect of atomic ordering and composition changes on the electrical resistivity of Nb3Al, Nb3Sn, Nb3Ge, Nb3Ir, V3Si and V3Ga

The electrical resistivity σohas been measured on a Nb3Ir sample, on a series of V3Si single crystals with compositions between 20 and 25.5 at.% Si and on two Nb3Al samples with the compositions β = 0.236 and 0.245. For Nb.755Al.245, σo= 48.2 × 10^-8Ωm was measured after quenching from 1940°C, a subsequent prolonged anneal at 750°C leading to a reduction of σoto 32.8 × 10^-8Ωm. It is found that σois more adequate than Tcin describing high TcA15 superconductors at near-stoichiometric compositions. A comparison of the behavior of σovs. β shows almost identical dependence for Nb3Ge and the two perfectly ordered systems Nb3Sn and V3Si thus suggesting perfect ordering for Nb3Ge, too. The systems Nb3Al and V3Ga are found to exhibit substantially higher σovalues, reflecting deviations from perfect ordering, Sa= 0.97 and S = 0.98, respectively. Consequences for the behavior of Bc2in high field A15 multifilamentary wires are drawn.