Electrical Conductivity Relaxations and Chemical Diffusivities of BaCe[sub 0.95]Yb[sub 0.05]O[sub 2.975] upon Hydration and Oxidation

Electrical conductivity relaxations were measured at a fixed temperature on proton-conducting upon sudden changes of oxygen activity in fixed water-vapor activity atmospheres and vice versa, in the ranges of and , respectively. It has been confirmed that the conductivity relaxes generally with two different relaxation times or twofold, but always nonmonotonically upon hydration/dehydration and monotonically upon oxidation/reduction. This twofold relaxation is attributed to the superposition of the two chemical diffusion processes of component H and O, driven by either the water or oxygen chemical potential gradient. The analytic solution to the conductivity relaxation, be it monotonic or nonmonotonic, is presented in closed form and thereby evaluated the two chemical diffusivities governing the hydration and oxidation kinetics, respectively.