Changes ofT c,J c,B c2 and the lattice parameter of the Nb3Sn phase formed at the initial stage of growth in a multifilamentary superconductive wire

Abstract

Investigations were made of the superconducting transition temperature,T c, the upper critical flux density,B c2, and the critical current density,J c, of Nb3Sn layers in filamentary wire in a bronze matrix. The lattice parameter,a 0, andT c of Nb3Sn layers in 259-filament wire were determined after removal of the bronze matrix. The microstructure and layer thickness were studied using scanning electron microscopy. The diffusion formation of Nb3Sn phase at 1023 K was studied until the complete reaction of the niobium filaments. It was found that the Nb3Sn layer begins to form in the manufacturing process during the intermediate annealing at 793 K, and that there is a considerable degradation of critical parameters due to the non-stoichiometry of the Nb3Sn phase in layers thinner than 1μm.