SYNTHESIS OF SUPERCONDUCTING PB/SB DOPED BISRCACUO COMPOUNDS VIA OXALATE COPRECIPITATION

An oxalate precipitation approach has been developed to synthesize superconductive Pb/Sb doped BiSrCaCuO materials. By computer modelling of the chemical equilibria, a laboratory routine has been established to produce these new class of high T(c) superconductors. The simultaneous and stoichiometrical precipitation of lead/strontium/calcium oxalates and bismuth/copper/antimony hydroxides (or oxides) has been carried out in an optimum pH range between 10-12. The coprecipitated oxalate/hydroxide composites are found to be ultra-fine powders with high homogeneity and low crystallinity. The sintered oxide pellets are characterized by X-ray diffraction analysis, scanning electron microscopy, electrical resistivity and magnetic susceptibility measurements. It is found that the Pb/Sb-doped samples synthesized via the oxalate route need a much shorter time for the heat treatment to form a high T(c) 2223-phase than the reference samples. On identical heat treatment, the superconducting properties of the oxalate-route samples are found to be superior to those produced by other methods both from T(c) and J(c) points of view. Our best Pb/Sb-doped samples processed at 830-degrees-C for 24 hours show a pure 2223-phase both from electrical resistivity (T(c) = 108 at zero resistance) and magnetic susceptibility measurements.