Effects of dopant concentration and aging on the electrical properties of Y-doped ceria electrolytes

High purity cerium oxide and yttrium oxide were used to form ceria-based solid solution (Ce1-xYxO2-δ, 0.05 ≤ x ≤ 0.4) via a conventional mixed-oxide method. All the samples used were aged at 1000 °C in air for 8 days. Crystal structure and microstructure were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ionic conductivity (i.e., grain interior (GI) grain boundary (GB) and total conductivities) in this system were systematically studied as a function of dopant content over the temperature range of 250-850 °C in air using an impedance spectroscopy. The lattice parameter decreased with increasing the Y content, but it did not obey Vegard's law. The Y doping had no significant effect on densification behavior and final sintered density, but leading to a significant decrease in grain size as compared to the undoped ceria. The composition x ≃ 0.1 had a maximum GI conductivity, while a maximum total conductivity was observed at x ≃ 0.15. A significant high-temperature aging effect was also found for the samples with higher Y doping levels. ∼ 10% and ∼ 15% decreases in the GI and GB conductivities, respectively, were detected in the aged Ce0.7Y0.3O2-δceramic.