Homogeneity of Superconducting Properties in Controlled Overpressure Processed Bi2223 Tapes

Recently, due to the controlled overpressure (CT-OP) sintering technique, performances such as critical current, $n$ -value, unit-length and mechanical strength of Ag sheathed $({\rm Bi,Pb})_{2}{\rm Sr}_{2}{\rm Ca}_{2}{\rm Cu}_{3}{\rm O}_{\rm x}$ (Bi2223) tapes were significantly enhanced. In order to investigate the origin of these improvements, we evaluated the distribution of the superconducting properties inside the tape along the width. We selected several kinds of CT-OP processed Bi2223 tapes and each tape was divided into three parts (one central part and two edge parts). We performed transport (critical current $I_{\rm c}$) and magnetic (susceptibility) measurements. We found that a slight inhomogeneity in superconducting properties still remains even in the highest performance tape, whose $I_{\rm c}$ is about 200 A at 77 K. Critical current densities $J_{\rm c}$ are lower at the edge part than those of the central parts. These results indicate that we can expect and achieve further improvements of CT-OP processed Bi2223 tape by enhancing the performance of the edge parts of the tape.