THE FORMATION OF SUPERCONDUCTING OXIDE PHASES IN THE (BI,PB)-SR-CA-CU-O SYSTEM

The crystallization mechanism of superconducting phases in the (Bi,Pb) -Sr-Ca-Cu-O sys tem was determined on the basis of the results of DTA, DTG and TG studies, supplemented by X-ray examination of ceramic powd ers obtained by the sol-gel method. It has been demonstrated that the factor determining the formation of superconducting phases: Bi2Sr2CaCu 2Ox (low-T-c) and Bi2Sr2Ca2CU3Ox (high-T-c) is the kinetics of reactio n of calcium and strontium carbonates with molten CuBi2O4. As a result of the reaction of the bimetallic compound CuBi2O4 With SrCO3 in the liquid phase the compound Bi2Sr2CuO6 is formed. This compound, reactin g with calcium and copper oxides, yields superconducting phases: the l ow-T-c and the high-T-c phase. It has been also observed that an incre ase in the volume fraction of high-T-c phase in powder subjected to th ermal treatment takes place probably due to the repeated disproportion ation of low-T-c phase and its repeated synthesis from Bi2Sr2CuO6, CuO and CaO.