Effect of 3221-Phase on Phase Formation and Superconducting Properties of Bi-2223/Ag Tapes

Abstract

Single phase (Bi,Pb)₃Sr₂Ca₂CuO_y (3221) was synthesised using a solid reaction method. Up to 10 wt% of 3221 powder was mixed with (Bi,Pb)₂Sr₂Ca₂Cu₃O_X (2223) precursor powders and silver-sheathed superconducting tapes were prepared using these powders by powder-in-tube technique. The phase formation, grain morphologies and impurity distributions were characterised by XRD and SEM. The electrical transport properties of the tapes were investigated in both a self-field and an external magnetic field. Although thermodynamically stable, the 3221 phase decomposes when mixed with 2223 precursor powder and sintered. Less-textured 2223 and an increased amount 2212 phase were found in the heavily-doped tapes. It is suggested that extra Pb in the 2223 matrix, arising from the 3221 phase decomposition, could affect the 2223 phase growth dynamics. Critical current declines dramatically with increasing concentration of 3221. This is ascribed to poor electrical connection of the 2223 grains arising from the decreased texture and also from the presence of 3221 and 2212 phases at grain boundaries.