Ionic conduction and nonstoichiometry in non-doped Ba_xCeO_3-α

Ionic conduction and Ba²⁺:Ce⁴⁺ site nonstoichiometry in perovskite-type oxide sinters of non-doped Ba_xCeO_3-α (0.90 ≤ x ≤ 1.10) have been investigated. X-ray powder diffraction patterns of these sinters indicated that the specimens with 0.95 ≤ x ≤ 1.10 were a single phase of orthorhombic perovskite-type BaCeO₃, while the sinter with x = 0.90 was a mixed phase of perovskite and CeO₂ impurity. The conduction properties of the specimens with 0.95 ≤ x ≤ 1.05 were studied electrochemically in the temperature range of 600-1000. The conduction properties of the specimens were strongly influenced by Ba²⁺:Ce⁴⁺ site nonstoichiometry. The specimens with excess Ba showed a predominant ionic conduction (H⁺ + O^2-) with ion transport number larger than 0.5 under hydrogen atmosphere, whereas they showed a poor oxide-ionic conduction (oxide-ion transport numbers < 0.1) under oxidizing atmosphere. Protonic conduction in these specimens under reducing atmosphere could be confirmed by means of electrochemical hydrogen permeation. In contrast, the specimens with x ≤ 1.00 showed a predominant oxygen-ionic conduction (oxygen-ion transport numbers > 0.8) in oxidative atmosphere, while a poor ionic conduction (ion transport numbers < 0.1) was observed in hydrogen.