SYNTHESIS OF (BIPB)(2)SR2CA2CU3OY SUPERCONDUCTORS BY THE SOL-GEL PROCESS

The sol-gel process is employed to synthesize single-phase lead-doped Bi2Sr2Ca2Cu3O10 ((Bi,Pb)-2223) superconductors. The composition which can yield single-phase (Bi,Pb)-2223 compound is arrived at by varying the calcium and copper concentrations. Samples prepared with the compo sition Bi-1.68 Pb0.32Sr1.75Ca1.8Cu2.8Oy result in the formation of pha se pure compound. The mechanism of formation of this compound and the intermediate steps involved during the phase formation are established by X-ray diffraction (XRD) and differential thermal analytical (DTA) studies. It is found that (Bi,Pb)-2223 phase formation occurs through the reaction of (Bi,Pb)-2212 phase with Ca2CuO3 and CuO in the liquid phase obtained from the partial melting calcium rich Bi-2212 phase. Th e stability region for the (Bi,Pb)-2223 compound is identified as 1118 to 1138 K. Several incongruent melting reactions are identified from XRD and DTA studies during the decomposition of Bi-2223 compound. (C) 1996 Academic Press, Inc.