Bulk protonic conduction in Yb- doped SrCeO3 and BaCeO3

The bulk protonic conductivity of SrCeO3 and BaCeO3 ceramics, each doped with 5% Yb3+ and treated in water vapor, was measured in the temperature range 25-250 C. In this range, the first arc in complex impedance analysis allowed determination of the true bulk conductivity; no distinct grain-boundary conductivity arc was observed. The activation energies obtained for proton migration were 0.63 eV for SrCeO3 and 0.51 eV for BaCeO3. The value of the pre-exponential factor indicates that the concentration of hopping protons is only a fraction of the concentration of Yb dopant. The isotope effect was investigated for SrCeO3 by replacing protons with deuterons; the activation energy then increased by 0.04 eV, indicating non-classical behavior. 4 refs.; 2 figs.; 2 tabs