Determination of Oxygen Chemical Diffusivity from Chemical Expansion Relaxation for BaCo0.7Fe0.22Nb0.08O3-δ.

The thermal and chemical expansion properties of BaCo_0.7Fe_0.22Nb_0.08O_3-δ, a potential candidate for oxygen permeable membranes and cathodes in solid oxide fuel cells, are reported here. The average thermal expansion coefficient is about 14 X 10^-6 K^-1 below 500°C, about 19 X 10^-6 K^-1 between 600 and 900°C, and about 29 X 10^-6 K^-1 between 900 and 1000°C, which consists of the previous weight change in a thermal gravimetric analysis experiment. The transient behavior in the thermochemical expansion can be best fitted with Fick's second law for a small displacement from the equilibrium. The chemical diffusivity of oxygen and the surface exchange kinetics are successfully extracted. [ABSTRACT FROM AUTHOR]