Analytical Study of Oxalates Coprecipitation

The paper deals with the establishing of the oxalates coprecipitation conditions in view of the synthesis of superconducting systems. A systematic analytical study of the oxalates precipitation conditions has been performed, for obtaining superconducting materials, in the Bi Sr-Ca-Cu-O system. For this purpose, the formulae of the precipitates solubility as a function of pH and oxalate excess were established. The possible formation of hydroxo-complexes and soluble oxalato-complexes was taken into account. A BASIC program was used for tracing the precipitation curves. The curves of the solubility versus pH for different oxalate excess have plotted for the four oxalates, using a logaritmic scale. The optimal conditions for the quantitative oxalate coprecipitation have been deduced from the diagrams. The theoretical curves were confirmed by experimental results. From the precursors obtained by this method, the BSCCO superconducting phases were obtained by an appropriate thermal treatment. The formation of the superconducting phases was identified by X-ray diffraction analysis.