Synthesis and magnetic field properties of transition metal substituted A-15 systems

We have been synthesizing high Tcsystems based on Nb3Ge in which another transition metal atom, either Mo, Ti, or Zr, is partially substituted for Nb. Systems have been prepared by selectively thermalized sputtering onto heated substrates. The systems investigated allow changes in Tcto be observed due to a variation in the electron per atom ratio as well as due to atom size effects. Superconducting transition temperatures are measured inductively which allows the identification of homogenous samples. Sample composition analysis is obtained by quantitative X-ray fluorescence. For the (Nb.99Zr.01)1-xGexsystem measurements of dHc2/ dT for fields up to 10 T for the resistive Tconset point went from 4.1 ±0.4 T/K to 2.6±0.3T/K as varied from 0.24 to 0.19. At x=0.23 the resistive Tconset was 18.9k (H=0). Extrapolation to 0 K for no Pauli paramagnetic limiting gives Hc2(T = 0 K) = 54 ± 5 T.