Investigation of superconductivity of niobium-tin alloys with high niobium content

Investigated were the microstructure, lattice spacing, chemical composition of phases and the superconductivity transition as indicated (by electric resistance values) in cast Nb-Sn alloys and in alloys annealed at 1800, 1000 deg C and double-annealed at 1800 and 1000 deg C in succession. Consideration of microstructure and X-ray analysis data and measurements of the critical temperature make it possible to conclude that the compound Nb3Sn is a phase of variable composition, that is capable of dissolving some niobium. The critical temperature of Nb3Sn phase heavily depends on the composition and varies at 18 deg K for a stoichiometric composition to 5.5-5.8 deg K for two phase alloys α+β. The minimum recorded critical temperature of the solid solution of tin in niobium with BCC lattice is 4.5 deg K