WATER SOLUBILITY, PROTON AND OXYGEN DIFFUSION IN ACCEPTOR-DOPED BACEO3 - A SINGLE-CRYSTAL ANALYSIS

From O-18-tracer diffusion, H-1-PFG-NMR and conductivity measurements, the diffusivities of protonic defects (OHo.) and oxygen ion vacancies (V-o(..)) in BaCeO3 single crystals doped with gadolinium and yttrium have been determined. Their dependence on the nature and concentratio n of the dopant, and the degree of hydration provide evidence for (i) a strong relaxation around oxygen ion vacancies which decreases with i ncreasing vacancy concentration and (ii) the absence of significant de fect interaction even for high dopant concentrations. The attempt freq uencies are consistent with a proton diffusion mechanism assisted by t he local oxygen dynamics. The thermodynamic data for the hydration rea ction, including the water solubility, are in accordance with the conc lusions drawn from the transport data. The hydration enthalpy is sugge sted to be determined not only by the formation enthalpy of oxygen ion vacancies but also by the basicity of the oxygen.