Effect of Ba nonstoichiometry on the phase structure, sintering, electrical conductivity and phase stability of Ba_1±xCe _0.4Zr_0.4Y_0.2O_3-δ (0≤x≤0.20) proton conductors

The influence of Ba nonstoichiometry on the phase structure, sintering, electrical conductivity and chemical stability under CO₂ atmosphere of proton conductors with a nominal composition of Ba _1±xCe_0.4Zr_0.4Y_0.2O _3-δ (B_1±xZCY4, 0 ≤ x ≤ 0.20) was systematically investigated. A complexing sol-gel process was applied to synthesize the B_1±xZCY4 powders. The X-ray diffraction patterns of the well-calcined powders indicate that the specimens with 0 ≤ x ≤ 0.10 possessed a single-phase of orthorhombic perovskite-type oxides. Additionally, impurity phases of (Y,Ce)O_2-δ existed in B _1-xZCY4, and BaCO₃ was found in B_1+xZCY4 with x = 0.15 and 0.20. After sintering at 1500 °C for 5 h, all B _1+xZCY4 samples became pure phased, whereas impurities still existed in samples with large Ba deficiencies. A study of the sintering behavior showed that the proper amount of Ba excess or deficiency facilitated electrolyte densification and that a large Ba nonstoichiometry hindered sintering. The electrical conductivities of B_1±xZCY4 specimens with 0 ≤ x ≤ 0.05 were studied in the temperature range of 100-700 °C, and the results showed that the Ba nonstoichiometry influenced the electrical conductivity, especially with respect to grain boundary resistance. The chemical stability was also studied using temperature-programmed CO₂ desorption, and it was determined that the chemical stability was affected by the Ba content.