Co-precipitation synthesis and AC conductivity behavior of gadolinium-doped ceria

Ce0.8Gd0.2O1.9 (GDC) powder was successfully synthesized using the co-precipitation process and the powder could be sintered to more than 95% of the theoretical density. This material was characterized using impedance spectroscopy, to distinguish the behavior of the grain interior and the grain boundary. AC impedance spectroscopy analysis was performed in the temperature range 300-800 °C. An Arrhenius plot of ln (σtT) vs. 1/T, for GDC sintered at 1500 °C, changes slope at around 573 °C. At low temperatures (300-573 °C), the total conductivity (σt) is dominated by the conductivity of the grain interior (σgi). However, at high temperatures (573-800 °C), the total conductivity (σt) is dominated by the conductivity of the grain boundary (σgb). The association enthalpy of the [Gd′Ce−VO··] clusters, ΔHa, calculated from ΔHa=Egilow−Egihigh, resulted equal to 0.448 eV. Elemental analysis, using inductively coupled plasma (ICP), shows that silicon exists in GDC ceramic. This suggests that the grain boundary resistance is related to the siliceous phases. These impurity SiO2 phases mainly originates from the raw materials.