AN IMPROVED COULOMETRIC TITRATION METHOD FOR OXYGEN-CONTENT AND VALENCE DETERMINATIONS IN BISMUTH AND LEAD CUPRATES

A two-step coulometric titration procedure originally published for the determination of the average valences of both copper and bismuth in the bismuth based cuprate superconductors was modified in order to avoid the effects of an observed harmful side reaction. Furthermore, the improved method was found to be applicable to the analyses of lead containing materials as well. The first titration experiment, which consists of the reactions of Cu(III), Bi(V), and Pb(IV) with Cu(I) followed by an anodic oxidation of the excess Cu(I), reveals the oxygen content of the sample. In the second experiment the valences of bismuth and lead are distinguished from the Cu-valence by taking advantage of the reaction with Fe(II). The selectivities of the proposed wet chemical processes were studied using YBa2Cu3Ov BiNaO3, PbO2, and Pb3O4 as reference materials for Cu(III), Bi(V), and Pb(IV), respectively. Additionally, the oxygen content and the average metal valences were determined in a single phase superconducting sample of (Bi, Pb)2Sr2CaCu2O2. © 1993 Academic Press, Inc.