TOWARDS THE RAPID SYNTHESIS OF PURE 2223-POWDERS WITH BI2-XPBXSR2CA2CU3OY COMPOSITIONS BY SEMI-WET METHODS .2. OPTIMIZATION OF PB CONTENT USING PB-SR-CA CARBONATE PRECURSORS

The effect of Pb content on the formation of the 2223 phase in stoichi ometric compositions Bi2-xPbxSr2Ca2Cu3Oy (0.1 less than or equal to x less than or equal to 0.4) is reported for a semi-wet route using [xPb CO(3) + 2SrCO(3) + 2CaCO(3)] precursors. Synthesis of high-purity 2223 phase free from Ca2PbO4 is reported for x = 0.3 within a total heat t reatment duration of 44 h with several intermediate crushings and grin dings. By studying the sequence of solid state thermochemical reaction s, it is shown that in the absence of Ca2PbO4, which plays a crucial r ole in accelerating the formation of 2223 phase, the conversion of 221 2 into 2223 gets slowed down unless one resorts to intermediate crushi ng and grinding. The optimum Pb content for the formation of 2223 phas e in Bi2-xPbxSr2Ca2Cu3Oy compositions has been estimated to be in the range 0.3 less than or equal to x less than or equal to 0.4.