New phase formation and superconductivity in reactively diffused Nb3Sn multilayer films.

Thin films of A15 Nb3Sn have been prepared by reactive diffusion of sputter- deposited Nb/Sn multilayers. The layers thicknesses were arranged in such a way as to produce Nb3Sn and desired of--stoichiometry samples. The reaction was studied by means of in situ temperature-dependent X-ray analysis in the range 50C-950C. It was observed that prior to the formation of the A15 phase, a very rapid reaction takes place between the Nb sublayers and molten Sn. In this reaction a new phase was observed which could be interpreted as a hexagonal Laves phase NbSn2. This phase transforms into orthorhombic NbSn2 which then reacts with the remaining Nb to form A15 Nb to form A15 Nb3Sn.