Characterization of cubic γ-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 γ-U phase retained at room temperature alongside the majority α-U phase and opening the possibility of stabilizing the γ-phase at room temperature in uranium metal by ultrafast cooling. The double-phase (α + γ) structure with predominance of the α-phase was obtained in the alloys with 0–10 at.% Mo. Increasing further Mo doping leads to the γ° phase (for 11–12 at.% Mo) and pure cubic γ 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 Tc in the range from 1.24 K (pure U splat) to 2.11 K (U-15 at.% Mo). The superconductivity in the γ-phase alloys exhibited a much higher upper critical field than for α-phase material. Electrical resistivity of the γ-alloys (⩾11 at.% Mo) exhibited a negative temperature coefficient from room temperature down to the superconducting transition.

► U-Mo alloys prepared by splat cooling.
► A small amount of γ-phase was preserved in pure splat-cooled uranium specimen.
► Crystal structure characterized by X-ray diffraction and EBSD.
► A stability of γ-phase for alloys with 11–15 at.% Mo.
► Superconducting transition, Tc = 1.24 K (pure-U) to 2.11 K (U-15 at.% Mo).