The extent of critical temperature variations of the superconducting phases in the BiPbSrCaCuO system

Bulk specimens having nominal composition of Bi 2-xPb xSr 2Ca 2Cu 3O y ( x = 0, 0.2,and 0.4) were subjected to various annealing and post-sinter cooling treatments to alter the oxygen stoichiometries and the granular critical temperature (T c) values of the superconducting phases. T c was found to vary from 53 K to 93 K in the 2212 phase and from 100 K to 108 K in the 2223 phase, depending on the processing. The shifts in the T c values of the two phases were not always in opposite directions as reported by others. Inferior intergranular coupling resulted when Ca 2PbO 4 precipitated into the grain boundaries during oxygen cooling, if the lead content was high ( x=0.4). The implications of these processing parameters on the bulk superconductive properties of this system are discussed.