Calculation of oxalate coprecipitation conditions for the synthesis of superconducting compounds

Purpose: The paper deals with the establishing of the oxalates coprecipitation conditions in view of the synthesis of superconducting systems. Methods: A systematic analytical study of the oxalates precipitation conditions has been performed, for obtaining superconducting materials in the BSCCO 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. Results: The curves of solubility versus pH for different oxalate excess have been plotted for the Cu(II)-, Bi(III)-, Ca(II)-, Sr(II)-, Ba(II)-, Y(III)-, Pb(II)-oxalates, using a logarithmic scale. For these diagrams, the optimal conditions for the quantitative oxalate coprecipitation have been deduced. The theoretical curves were confirmed by experimental results. From the precursors obtained by this method the BSSCO superconducting phases were obtained by an appropriate thermal treatment. The formation of the superconducting phases in the system was identified by X-ray diffraction analysis. Conclusions: The theoretical solubility diagrams can be used in order to establish the optimal conditions for obtaining the precursors for superconducting materials. (orig.)