Superconducting behavior of Nb3Ge1-xGaxfilms obtained by chemical vapor deposition

Films of Nb3Ge1-xGax(x = 0 to 1) with the A-15 structure were obtained on hastelloy, copper and quartz substrates by chemical vapor deposition. The bulk alloys of composition Nb3Ge1-xGaxwere first chlorinated and subsequently reduced by hydrogen to form the thin films. The ratio of H2/Cl2flow rates and the residence time of the gas were optimized to obtain single phase A-15 films. Films of composition Nb3Ge.75Ga.25exhibited a very sensitive dependence of Tcon the H2/Cl2flow rate. Tcof Nb3Ge.75Ga.25was found to increase very rapidly with decreasing lattice parameter. The highest Tcobtained for Nb3Ge.75Ga.25films was 18 K. Films of composition Nb3Ge.5Ga.5and Nb3Ge.25Ga.75had relatively low Tc(4 to 8 K). The dependence of Tcon lattice parameter for the various compositions was found to be in good agreement with the universal defect behavior of A-15 compounds proposed by Noolandi and Testardi.