Electromagnetic granularity, critical current density, and low-Tc phase formation at the grain boundaries in (Bi,Pb)2Sr2Ca2Cu3Oχ silver-sheathed tapes

Abstract Transport critical currents are correlated with DC magnetization, AC susceptibility and high resolution electron microscopy in progressively heat treated Ag-clad (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O χ (2223) tapes. Both the zero field cooled magnetization shielding curves and the real component of the AC susceptibilities show two diamagnetic transitions. One transition is found to occur at 109 K and is the signature of the 2223 phase. A second, much larger transition occurs over a range of temperatures between 75 and 105 K. The transport critical current densities correlate directly with the lower magnetic transition temperature. High resolution electron microscopy reveals a few layers of Bi 2 Sr 2 CaCu 2 O χ (2212) phase clustered at the numerous (001) twist grain boundaries. These residual layers require a long reaction for their elimination and directly control the critical current while they are present.