Effect of annealing on the superconducting and normal state properties of the doped multifilamentary Cu–Nb composite wires prepared by in situ technique

The effect of annealing on the superconducting and normal state properties of the Ga-, In-, Ti- and Zr-doped (1 wt%) Cu–Nb composite wires prepared by in situ technique have been investigated in this paper. The wires annealed at 700°C for 10 h and then quenched at room temperature, show a decrease in the superconducting transition temperature, T c, and increase in the transition width, Δ T. Doping of the Cu–Nb wires causes an increase in the normal state resistivity and hence the upper critical field, H C2. This results in a significant increase of J c. Annealing of these doped samples decreases H C2 and J c. In the case of In- and Ga-doped samples J c shows a marginal improvement at lower field but decreases at higher field. Zr and Ti doping appears to be beneficial for the improved J c in these in situ materials.