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

Abstract

The influence of Ba nonstoichiometry on the phase structure, sintering, electrical conductivity and chemical stability under CO 2 atmosphere of proton conductors with a nominal composition of Ba 1± x Ce 0.4Zr 0.4Y 0.2O 3− δ (B 1± x ZCY4, 0 ≤ x ≤ 0.20) was systematically investigated. A complexing sol-gel process was applied to synthesize the B 1± x ZCY4 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− x ZCY4, and BaCO 3 was found in B 1+ x ZCY4 with x = 0.15 and 0.20. After sintering at 1500 °C for 5 h, all B 1+ x ZCY4 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± x ZCY4 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 CO 2 desorption, and it was determined that the chemical stability was affected by the Ba content.