Ionic conductivity in the CeO₂-Gd₂O₃system (0.05 ≤ Gd/Ce ≤ 0.4) prepared by oxalate coprecipitation

High purity cerium and gadolinium salts were used to form ceria-based solid solution (Ce1-xGdxO2-δ, 0.05 ≤ x ≤ 0.4) through the oxalate coprecipitation. Crystal structure and microstructure were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ionic conductivity (i.e., lattice, grain boundary (GB) and total conductivities) in this system were systematically studied as a function of dopant content over the temperature range from 200 to 850 °C in air using an impedance spectroscopy. The grain boundary conductivity increases rapidly at x<0.1 and is almost unchanged between x = 0.1 and x = 0.2, then decreases at x > 0.2. The Gd content has a slighter influence on the lattice conductivity in the Gd content ranging from 0.05 to 0.2, while a rapid decrease in the lattice conductivity is observed at x > 0.2. A maximum total conductivity is observed for the composition x = 0.2.