Variation of Tcof sputtered Nb3Ge

Alloy samples of Nb and Ge were prepared by simultaneous R. F. sputtering of composite Nb-Ge targets onto heated alumina substrates. The variation of the superconducting transition temperature Tcand the X-ray properties of these specimens were studied as a function of the alloy composition, in the neighborhood of Nb3Ge. The variation of the sputtering parameters, i.e., the self bias voltage, the sputtering gas pressure and the substrate temperature was also studied. Results indicate that high Tcoccur for well-ordered stochiometric Nb3Ge alloys. It was also found that the competing tetragonal phases are promoted by the highly energetic atoms i.e. at high sputtering rates. The relative sticking probability of Ge is important at the higher substrate temperatures.