SUPERCONDUCTING PROPERTIES OF A-15 V75-XMXGA25 COMPOUNDS - M = TI, CR, MN, FE, CO, AND NI

Superconducting transition temperatures Tc and their pressure derivatives dTcdp have been determined for V3Ga based ternary compounds containing 3d-element substitutions for V. The superconducting transition temperatures decrease while the normalized pressure derivatives, (1Tc)(dTcdp) increase systematically for all 3rd element additions. These results suggest that the form of the Tc equation is not affected by rapid variations in the electronic density of states N(E), as suggested by some models for superconductors of the A-15-structure type. Analysis of the data in terms of the McMillan Tc equation and the more recent Tc equation of Birnboim show that the electron-phonon coupling parameter λ scales uniquely with the electron-per-atom ratio z and is approximately proportional to the electronic density of states at the Fermi level, N(EF). The volume derivative of λ, as determined from dTcdp data, remains approximately constant as the electron-per-atom ratio varies near that of V3Ga (z=4.5). The only significant difference in the two model Tc equations, i.e., McMillan or Birnboim, is in the absolute values of the parameters λ and dlnλdlnV, not in systematic variations. © 1979 The American Physical Society.