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 compou nds with and without the addition of Pb were synthesized, and their th ermal stability and melting relations in air were studied. DTA, XRD an d SEM/EDX microstructure analysis were used in these studies. The 2201 phase without Pb melts above 890 degrees C while the Pb-doped 2201 ph ase 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 2 212 phase melts above 870 degrees C. Melting of the 2212 phase leads t o formation of the 2201 and (Sr, Ca)CuO2 phases. The Pb-doped 2223 pha se 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 te mperatures above 880 degrees C the 2223 phase decomposes completely. T he (Ca, Sr)(2)CuO3 phase and the (Sr, Ca)(14)Cu24O41 phase are also fo rmed in the process of decomposition of the 2223 phase.