Four-probe direct-current measurements were carried out on polycrystalline material with the composition, Ba3Ca1.18Nb1.82O9–δ. These showed that the conductivity changed linearly with time during the initial stages, when the atmosphere was changed from dry air to wet air, or vice versa. In order to analyze this transient conductivity change with time, a model was developed which assumed a rapid surface reaction. The model was then used to fit experimental plots of conductivity versus time, and to estimate the chemical diffusion coefficient of H2O at 400 to 900C. The temperature dependence of the chemical diffusion coefficient could be described by an Arrhenius equation, with an activation energy of about 0.80eV.

Estimation of the Chemical Diffusion Coefficient of H2O in Ba3Ca1.18Nb1.82O9–δ from Conductivity Measurements. W.Wang, A.V.Virkar: Journal of the Electrochemical Society, 2003, 150[1], A92-7