Strontium doping effect on phase homogeneity and conductivity of Ba _1-xSr_xCe_0.6Zr_0.2Y _0.2O_3-δ proton-conducting oxides

Ba_1-xSr_xCe_0.6Zr_0.2Y _0.2O_3-δ (0.0 ≤ x ≤ 1.0) proton-conducting oxides have been prepared using a citrate-EDTA complexing solegel method. In this study, the relationship between the Sr doping content and microstructure, chemical stability against CO₂, and conductivity of the sintered Ba_1-xSr_xCe_0.6Zr_0.2Y _0.2O_3-δ pallets are systematically investigated using XRD, SEM, micro-Raman spectroscopy, and dc two-probe measurements. All sintered Ba_1-xSr_xCe_0.6Zr_0.2Y _0.2O_3-δ oxides exhibit excellent chemical stability after being exposed to the CO₂ ambient at 600 °C for a long duration; nevertheless, their microstructures and conductivities are very sensitive to the Sr doping amount. The Sr incorporation is found to apparently suppress the formation of CeO₂-like second phase, and enhance the grain growth in sintered oxides. Among all sintered samples, the Ba _0.8Sr_0.2Ce_0.6Zr_0.2Y _0.2O_3-δ pallet has the highest conductivity, 0.009 S/cm at 800 °C. This result can be attributed to the competition between the elimination of CeO_2- or (Zr,Ce,Y)O₂-like phase inhomogeneity and enhanced grain growth in sintered oxides, both of which adversely influence the ionic conductivity. This work demonstrates that Ba _1-xSr_xCe_0.6Zr_0.2Y _0.2O_3-δ would be a promising electrolyte for H ⁺-SOFC applications if the Sr doping iswell controlled.