Superconducting primary substitutional solid solutions, consisting of niobium, vanadium or tantalum (column V of the periodic table) alloyed with a metal of column IVA or VIA, show interesting correlations between size of solute and (a) lattice parameter, (b) critical temperature, (c) critical current, (d) coefficient of electronic specific heat, and (e) the Debye characteristic temperature. Solute atoms larger than the matrix atoms increase (a), (b), (c), and (d), but decrease (e). Solute atoms smaller in size decrease (a), (b), (c), and (d), but increase (e). $T_c$ is found to correlate better with an effective $\frac{e}{a}$ ratio, that contains a sizedependent correction than with the usual $\frac{e}{a}$ ratio. Magnetization studies indicate that these alloys approach an Abrikosov type of behavior when the sample is in powder form. In bulk form hysteresis is influenced by the relative size of solute and matrix atoms.

• Received 1 February 1963

DOI:https://doi.org/10.1103/PhysRev.130.2177