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

The electrical resistivity σ
o
has been measured on a Nb
3
Ir sample, on a series of V
3
Si single crystals with compositions between 20 and 25.5 at.% Si and on two Nb
3
Al samples with the compositions β = 0.236 and 0.245. For Nb
.755
Al
.245
, σ
o
= 48.2 × 10
^-8
Ωm was measured after quenching from 1940°C, a subsequent prolonged anneal at 750°C leading to a reduction of σ
o
to 32.8 × 10
^-8
Ωm. It is found that σ
o
is more adequate than T
c
in describing high T
c
A15 superconductors at near-stoichiometric compositions. A comparison of the behavior of σ
o
vs. β shows almost identical dependence for Nb
3
Ge and the two perfectly ordered systems Nb
3
Sn and V
3
Si thus suggesting perfect ordering for Nb
3
Ge, too. The systems Nb
3
Al and V
3
Ga are found to exhibit substantially higher σ
o
values, reflecting deviations from perfect ordering, S
a
= 0.97 and S = 0.98, respectively. Consequences for the behavior of B
c2
in high field A15 multifilamentary wires are drawn.