Characterization of cubic gamma-phase uranium molybdenum alloys synthesized by ultrafast cooling

U-Mo alloys with Mo concentration in the range of 0-15 at.% Mo were prepared using a splat-cooling technique. Phase analysis using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron back-scatter diffraction (EBSD) revealed the presence of a small amount of gamma-U phase retained at room temperature alongside the majority alpha-U phase and opening the possibility of stabilizing the gamma-phase at room temperature in uranium metal by ultrafast cooling. The double-phase (alpha + gamma) structure with predominance of the alpha-phase was obtained in the alloys with 0-10 at.% Mo. Increasing further Mo doping leads to the gamma degrees phase (for 11-12 at.% Mo) and pure cubic gamma phase (for 15 at.% Mo). The superconducting transition was investigated by low-temperature resistivity measurements down to 0.3 K in magnetic fields up to 5 T. All the splats become superconducting with T-c in the range from 1.24 K (pure U splat) to 2.11 K (U-15 at.% Mo). The superconductivity in the gamma-phase alloys exhibited a much higher upper critical field than for alpha-phase material. Electrical resistivity of the gamma-alloys (>= 11 at.% Mo) exhibited a negative temperature coefficient from room temperature down to the superconducting transition. (C) 2012 Elsevier B. V. All rights reserved.