A study of the H c 2 enhancement due to the addition of Ti to the matrix of bronze-processed Nb3Sn superconductors

The measurements of ρn (the normal state resistivity), Tc, Hc2, and (dHc2/dt)T=Tc have been made for bronze-processed Nb3Sn wires with addition of Ti to the Cu-Sn matrix in order to study the mechanism of Hc2 enhancement due to the addition of Ti. The coefficient of electron specific heat, γ, has been derived by two independent methods: one using the Ginzburg–Landau–Abrikosov–Gor’kov (GLAG) theory and the measured values of ρn, Tc, and (dHc2/dT)T=Tc, and the other using the Kramer pinning theory and the gradient of J1/2cH1/4 -H curves. The ratios of γ/γ0 which have been derived by these two methods are in good agreement with each other. (γ0 is the value of γ for the specimen to which Ti is not added.) The upper critical fields given by the GLAG theory, H*c2 and Hc2, at 0 K increase rapidly with Ti concentration in the Nb3Sn layer up to 2 at. % and decrease slightly above 2 at. %. The rapid increase in ρnγTc caused by the addition of Ti is sufficient to explain the enhancement in Hc2, and among ρn, γ and Tc, only ρn shows a significant increase with increasing amounts of additional Ti, indicating that the main reason for the Hc2 enhancement is the increase in ρn.