THE THERMAL-STABILITY OF BI SUPERCONDUCTORS IN THE BI(PB)-SR-CA-CU-O SYSTEM

In the Bi-Sr-Ca-Cu-O system 2201, 2212 and 2223 superconducting compounds with and without the addition of Pb were synthesized, and their thermal stability and melting relations in air were studied. DTA, XRD and SEM/EDX microstructure analysis were used in these studies. The 2201 phase without Pb melts above 890 degrees C while the Pb-doped 2201 phase starts to melt above 880 degrees C. Similarly Pb doping decreases the melting point of the 2212 phase by 10-15 K and the Pb-containing 2212 phase melts above 870 degrees C. Melting of the 2212 phase leads to formation of the 2201 and (Sr, Ca)CuO2 phases. The Pb-doped 2223 phase is stable up to 865 degrees C; above this temperature it decomposes. In the temperature range between 865 degrees C and 880 degrees C the 2223 phase coexists with the 2212 phase and the 2201 phase, and at temperatures above 880 degrees C the 2223 phase decomposes completely. The (Ca, Sr)(2)CuO3 phase and the (Sr, Ca)(14)Cu24O41 phase are also formed in the process of decomposition of the 2223 phase.