Enhancement of the upper critical field of Nb3Sn utilizing disorder introduced by ball milling the elements

Nb3Sn was prepared by milling Nb and Sn powder mixtures followed by limited reactions to restrict disorder recovery. Although disorder reduced the superconducting critical temperature Tc, the concomitant electron scattering increased the upper critical field mu0Hc2 to as high as 35 T at 0 K, as determined by the Werthamer-Helfand-Hohenberg equation. Hc2 was higher for longer milling times and lower annealing temperatures. Substitution of 2% Ti for Nb did not appreciably enhance Hc2, suggesting that alloying mitigates the benefits of disorder. Since alloyed Nb3Sn wires have mu0Hc2(0) approximately 29 T, wires based on heavily milled powders could extend the field range for applications if they can be made with high current density.