SUPERCONDUCTING T(C)S AND PHASE RELATIONSHIPS OF SPUTTER-DEPOSITED NB3GE

Nb3Ge which is fully superconducting above 21 K has been prepared by sputter deposition in a very clean vacuum system at substrate temperatures in the range 500-550°C, or 200°C less than the temperatures needed in other sputtering systems. For a series of compound targets, superconducting Tc's and metallurgical phases, as established from x-ray diffraction studies, were determined as a function of substrate temperature and argon pressure. Maximum Tc's were found in films prepared over a narrow range of compositions and substrate temperatures. These conditions coincide with the region of phase stability for the A15. A small amount of oxygen (≳1.0%) as determined by Auger analysis, was found to be present in high-Tc films, while lower Tc films all had less oxygen.