New Nb3Al-based A15 multifilamentary wires with high Jc in high fields

When Nb/Al–X (X=Ge or Cu) microcomposite precursor wires were rapidly heated and quenched, disordered Nb3Al-based A15-phase filaments formed. With annealing at 750–800°C, their superconducting properties improved drastically. The Nb3Al-based A15 wire, with Ge or Cu added, showed a maximum value of Tc=19.4 or 18.2 K, and that of Hc2 (4.2 K)=39.5 or 28.7 T, respectively, which are higher than the maximum values of Tc=17.9 K and Hc2 (4.2 K)=25.8 T for the rapid heating, quenching and transforming (RHQT)-processed Nb3Al wire without additional elements. In addition, the new superconductors showed higher Jc than that of the RHQT-processed Nb3Al multifilamentary wire in high fields.