Ionic conductivity of high-purity Gd-doped ceria solid solutions

The Ce1−xGdxO2−δ (0.02 ≤ x ≤ 0.3) solid solutions with ∼30 ppm SiO2 were prepared through the conventional mixed-oxide method from high-purity CeO2 and Gd2O3 powders. The ionic conductivity (especially the grain boundary (GB) conduction) in this system was studied as a function of dopant content, over the temperature range of 250–750 °C in air, using an impedance spectroscopy. The GB impedance played an important role in the total conduction in the samples with low Gd content (usually x ≤ 0.1), but decreased sharply with increasing Gd content. Both the total and GB conductivities maximized at the composition x = 0.15, and this composition also had the lowest activation energies for the total and GB conduction. The maximum total conductivity at 700 °C, σt = 4.07 (Ω m)−1 with the activation energy, Et = 0.77 eV, was found for the composition x = 0.15.