Critical temperatures of superconductivity and neutron diffraction studies at 293 and at 10 K of molybdenum-iridium single crystals of A15 structure

A crystal of dimensions 2.5 × 2.5 × 1.8 mm and of composition Mo_3.25Ir was examined by neutron diffraction at 293 and 10 K. It has the A15 structure for which the space group is Pm3n and the ideal composition would be Mo₃Ir. Least-squares refinements gave R(F) values of 0.013 and 0.017 for the 293 and the 10 K data, respectively. No structural phase transition was observed at 10 K. The lattice constants found were a = 4.967 (2) Å at 293 K and 4.958 (2) Å at 10 K. The transition temperature to superconductivity of the crystal was measured by an inductive method. An onset of superconductivity was found at 9.25 (5) K and a main transition at 9.10 (5) K. Another, approximately cylindrical, sample of volume 117 mm³ showed an onset at 8.6 (1) K and a main transition at 8.0 (1) K. About two thirds of this sample was a single-crystal.