Calculation of Oxalate Coprecipitation Conditions for the Synthesis of Superconducting Compounds

The optimum oxalate coprecipitation conditions for synthesising BSCCO system superconductors were systematically analysed. The formulae of the precipitates solubility were established as a function of pH and oxalate excess. Possible formation of hydroxo-complexes and soluble oxalato-complexes was taken into account. A BASIC program was used to trace the precipitation curves. The curves of solubility versus pH for different oxalate excess were plotted for the Cu(II)-, Bi(III)-, Ca(II)-, Sr(II)-, Ba(II)-, Y(III)-, and Pb(II)-oxalates using a logarithmic scale. Optimal conditions for quantitative oxalate coprecipitation were deduced for these diagrams. The theoretical curves were confirmed by experimental results. From the precursors obtained by this method, BSCCO superconducting phases were obtained by appropriate heat treatment. Formation of the superconducting phases in the system was determined by XRD. The theoretical solubility diagrams can be used to establish the optimal conditions for obtaining precursors for superconducting materials. 14 refs.