Synthesis of (BiPb)<inf>2</inf>Sr<inf>2</inf>Ca<inf>2</inf>Cu<inf>3</inf>O<inf>y</inf> 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 composition Bi1.68 Pb0.32Sr1.75Ca1.8Cu2.8Oy result in the formation of phase 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. The 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. © 1996 Academic Press, Inc.