SUPERCONDUCTING BEHAVIOR OF NB3GE1-XGAX FILMS 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-xGax were first chlorinated and subsequently reduced by hydrogen to form the thin films. The ratio of H2/C12 flow rates and the residence time of the gas were optimized to obtain single phase A-15 films. Films of composition Nb3Ge 75Ga#25 exhibited a very sensitive dependence of Tc on'the H2/C12 flow rate. Tc of Nb3Ge,75Ga25 was found to increase very rapidly with decreasing lattice parameter. The highest Tc obtained for Nb3Ge7sGa,25 films was 18 K. Films of composition Nb3Ge,sGa,5 and Nb3Ge.25Ga.75 had relatively low Tc (4 to 8 K). The dependence of Tc on 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. © 1979 IEEE