Critical temperature of superconductivity and X-ray crystallographic studies of Nb0.78Al0.17Ge0.05 of A15 structure

Compounds of niobium and aluminium and of niobium, aluminium and germanium which crystallize in the A15 structure were prepared by sintering and by floating-zone methods. Single crystals of up to 1x1x1 mm were obtained for the composition Nb0.78Al0.17Ge0.05. Transition temperatures to superconductivity ranged from midpoint values of 18.6 to 19.4 K over intervals of 3 K. Single-crystal X-ray diffraction measurements were made at 293 and at 11-12 K. Powder diffractometer data were obtained at 293 K. The structure was refined with both powder data (Rietveld technique) and single-crystal data. Photographic powder patterns were obtained from room temperature down to 11.7 K. No phase transition was observed. No evidence was found for deviations from the A15 structure. (orig.)