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

We have been synthesizing high T
c
systems based on Nb
3
Ge 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 T
c
to 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
.99
Zr
.01
)
1-x
Ge
x
system measurements of dHc
2
/ dT for fields up to 10 T for the resistive T
c
onset 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 T
c
onset was 18.9k (H=0). Extrapolation to 0 K for no Pauli paramagnetic limiting gives H
c2
(T = 0 K) = 54 ± 5 T.