Phase diagram studies in the system Bi-Pb-Sr-Ca-Cu-O-Ag

Phase diagram studies with emphasis on the high temperature superconducting phases Bi2+xSr2-yCa1+yCuO8+d (2212 phase) and (Bi,Pb)(2+x)Sr2-yCa2+yCuO10+d (2223 phase) are reviewed in this article. The phase relations of the Bi2O3-SrO-CaO-CuO and the homogeneity regions of the 2212 and 2223 phases have been studied in detail at various temperatures and oxygen partial pressures. However, the Pb-doped system has been investigated less comprehensively. The studies of this system are mostly focused on the 2212 and 2223 phase and the experimental work regarding the 2223 phase is often concentrated on the processing of 2223 samples with high critical current density and not on the preparation of single phase 2223 ceramics. The investigations of the Ag-containing system have just started. Nevertheless, first results show that Ag significantly influences the phase relations and the temperature dependence of the cation solubilities of the 2212 and 2223 solid solutions. These results indicate that the obtained phase diagrams of the system Bi2O3-PbO-SrO-CaO-CuO cannot be applied without caution when Ag is present. Therefore, as Ag is widely used as a sheath material for the processing of 2212 and 2223 wires and tapes, the investigation of the entire Ag-containing system is inevitable.