The effects of composition and order on the superconducting properties of the A-15 phase of Nb-Pt

The effect of composition and order on the superconducting transition temperature, Tsub(c), and lattice parameter, asub(0), of the A-15 phase of Nb-Pt is reported. Tsub(c) is found to be sharply peaked at the stoichiometric composition, falling off roughly linearly with an average slope of about 1.5 K per at.% on both sides of stoichiometry. The observed lattice parameters for the A-15 phase field can be explained on the basis of a modified Geller model in which the effective radius of a Nb atom depends upon whether it occupies a Nb or Pt site. (author)