Improvement of critical currents in Bi-2223 bulk superconductors

Potential applications of the high-Tc superconductors for energy transport or high-field magnets require high critical current densities. A limiting factor in polycrystalline oxidic materials is the quality of the grain boundaries. Weak links have been made responsible for the steep decrease in the critical current density jc upon application of even weak magnetic fields of YBa CuO whereas flux creep seems to dominate the obtainable jc values for the Bi-Sr-Ca-Cu-O system (BSCCO) at 77 K. In the lead containing material (BPSCCO) the formation of a porous microstructure is enhanced by the platelike shape of the crystals. Special techniques such as powder-in-tube, hot isostatic pressing, zone melting or application of fluxes have been used in order to improve the grain contacts. A positive influence of fluxes on jc, e.g. by addition of Ca2CuO3 or Ag2O, has been reported. In this study we have investigated the influence of various compositions and conditions on the formation of the BSCCO-2223 phase (Tc ca. 107 K), the critical current density jc, and the magnet field dependence of the a.c. susceptibility. (orig.)