2223 PHASE FORMATION IN BI(PB)-SR-CA-CU-O .3. THE ROLE OF ATMOSPHERE

The formation of second phases during the preparation of the 2223 phase and their stability in the Bi system under various annealing temperatures and atmospheres have been studied. The 2201 precipitates developed at approximately 830-degrees-C, and their conversion to the 2223 phase can be completed in the temperature range 810-degrees-C less-than-or-equal-to T < 830-degrees-C. A Ca2PbO4-like phase can precipitate from the liquid phase at approximately 830-degrees-C during cooling. A (Sr,Ca)14Cu24O41 phase is usually found accompanying the synthesis of the 2223 phase. This secondary phase is stable in an oxidizing atmosphere but can be eliminated by annealing under a low oxygen atmosphere or by choosing a suitable starting composition and set of sintering conditions. The precipitation of Ca2PbO4-like phase can be avoided by using a relatively fast cooling rate. Unlike the YBa2Cu3Ox superconductor, the 2223 phase can be stable under a wide range of atmospheres, such as argon, air, and oxygen.