ANIONIC CONDUCTION PROPERTIES OF BI-CA-PB MIXED OXIDES

This study of the Bi2O3-CaO-PbO system has determined the equilibrium domains of existence of three solid solutions which belong respectively to the fcc (delta-Bi2O3), rhombohedral (Bi-Sr-O) and bcc (anti-alpha-AgI) structural types. The first two solid solutions can be preserved at room temperature in a metastable or/and a stable form within a significant range of composition. They have been investigated by impedance spectroscopy and transport number measurements. In all cases, the substitution of Bi3+ by the divalent cations leads to a decrease of the conductivity. However, for a constant M2+ concentration, the conductivity increases slightly with the Pb2+/Ca2+ ratio without significant modification of the activation energy. Transport number measurements, performed particularly on the delta-phase, have shown, at low temperature (less-than-or-equal-to 400-degrees-C), a very attractive quick response to any P(O2) variation. The corresponding Nernst potentials were shown to be significantly higher than expected from the classical O2/O2- electrode equilibrium.