Critical temperature of superconductivity and X-ray crystallographic studies of Nb_0.78Al_0.17Ge_0.05 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 1 × 1 × 1 mm were obtained for the composition Nb_0.78Al_0.17Ge_0.05. 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.