TEMPERATURE-DEPENDENCE OF THE PHASE RELATION IN THE BI-PB-SR-CA-CU-O SUPERCONDUCTING CERAMICS

The phase relation and the microstructural features in Bi-Pb-Sr-Ca-Cu-O superconducting ceramics have been investigated. Various samples were prepared by sintering at temperatures between 1073 and 1223 K for a long time and quenching into liquid nitrogen. The phases existing at those temperatures have been identified by means of XRD and EPMA. The 2223 phase was found to be formed by the reaction of the 2212 phase with the liquid, which is produced eutectically from the 2201 phase and Ca2PbO4. It was confirmed that the volume fraction of the 2223 phase became largest in the sample sintered at 1128 K, with small amounts of impurity phases CuO, (Sr, Ca)2CuO3 and (Sr, Ca)3Cu5O(x). The amounts of (Sr, Ca)2CuO3 and (Sr, Ca)CuO(x) phases increased during the decomposition of the 2223 phase at temperatures above 1133 K. The (Sr, Ca)O(x) compound was identified as a new phase for the sample sintered at temperatures higher than 1223 K.