Transport study of the solid electrolyte BaCe_0.9Gd_0.1O_2.95 at high temperatures

Doped barium cerate perovskites are of interest as electrolytes for solid oxide fuel cells operating at 600–1000°C. Moreover, in this temperature range they display a transition from protonic to oxide ion conduction. In this study, the conductivity of BaCe_0.9Gd_0.1O_2.95, previously reported only up to 800°C, was measured up to 1200°C using the a.c. van der Pauw technique. Data obtained in a range of atmospheres and plotted against log(P_O2) displayed ionic, p-type and n-type components, which could be resolved by curve fitting to standard conductivity equations. The activation energies of the three components, estimated separately, were 0.52 eV for σ_i, 0.64 eV for σ_p and 2.6 eV for σ_n. These parameters were used to calculate the ionic transport number under high P_O2, and low P_O2, conditions and to map out the compound's ionic domain. The ionic transport numbers obtained for low and high oxygen partial pressures have been compared to those measured previously using concentration cells.