Influence of ZnO doping on superconductivity and crystal structure of (Bi, Pb)-2223 superconductor

The crystal structures of the high-Tc (2223) phase with ZnO were refined using Rietveld analysis in order to clarify the possibility of Zn substitution for Cu sites. In addition, the effects of ZnO doping on the Bi-2223 phase were investigated by means of evaluations of the superconducting properties. From the results of the Rietveld analysis, it is suggested that the variations in the lattice parameter are mainly due to those in the atomic distances of the CuO5 pyramid induced by Zn substitution for Cu(2) site in the Bi-2223 phase, indicating the lattice parameters, b and c, of the ZnO-doped Bi-2223 phase by increasing ZnO content are decreased, whereas the lattice parameter a is increased. The solid-solubility of Zn in the Bi-2223 phase is estimated ∼ 2 wt.% from the variations in the lattice parameters. From the experimental results of the ZnO-doped Bi-2223 phase, it was clarified that the melting temperature of the Bi-2223 phase is lowered and critical temperature (Tc) is not affected.