Evaluation of electrode-oriented properties of BaFe1−xCexO3−δ.

The structure, oxygen non-stoichiometry, thermomechanical and electrical properties of perovskite-type BaFe_1−xCe_xO_3−δ (x = 0.05, 0.10, 0.15) were studied in the light of the potential use of these oxides as electrode materials of solid oxide fuel cells. Partial substitution of iron by cerium in barium ferrite was shown to stimulate water incorporation into oxygen vacancies. This phenomenon is manifested by dehydration during heating, which is clearly registered by thermogravimetric and dilatometric measurements. Different behavior of cerium ions residing in the A- and B-sublattices of perovskite-type ferrites was revealed. In contrast to Sr_1−xCe_xFeO_3−δ oxide series, in which the concentration of Ce³⁺ ions under reducing conditions can exceed that of Ce⁴⁺, no signs of Ce⁴⁺ reduction were detected in BaFe_1−xCe_xO_3−δ under the same conditions. A negative influence of cerium substitution for iron on electrical conductivity was detected. The oxygen-ion conductivity of the x = 0.05 composition at 950 °C was found to be as high as 0.358 ± 0.002 S·cm⁻¹, whereas the ion conductivity of the oxide with x = 0.10 was only 0.041 ± 0.001 S·cm⁻¹. Such a strong suppression of oxygen transport is argued to be the result of a local lattice strain caused by a considerable difference between the sizes of cerium and iron ions. The unfavorable impact of cerium in BaFe_1−xCe_xO_3−δ on n- and p-type conductivity is attributed to its impeding role in the Fe–O–Fe electron transport network. [ABSTRACT FROM AUTHOR]