Phase transitions and superconducting properties of binary and Ti, Ta, Ga and H alloyed Nb 3Sn

Abstract

The low temperature phase transformation in Nb 3Sn has been analyzed for various samples (bulk and multifilamentary) with the additions Ta, Ti, Ga, H by means of X-ray powder diffractometry. The transformation behavior of Nb 3Sn with and without additions was studied on powdered 19-core filaments of bronze-processed wires which were previously characterized by measurements of J c, T c and the electrical resitivity ϱ 0. A lattice transformation was observed for the binary Nb 3Sn, for 0.9 at.% Ga and 1.3 at.% Ta, while no transformation was found for an effective Ta, Ti and H content of 4.3, 1.3 and 0.6 at.%, respectively. It is found that the suppression of the lattice instability by additives is not uniquely correlated to lattice parameter variations with respect to binary Nb 3Sn. A necessary additional criterion is the chemical nature of the additive, which determines its position on the 6c sites (e.g. Ta, Ti) or on the 2a sites (e.g. Ga, Al, Sb, Ni).