Grain boundary conduction of Ce0.9Gd0.1O2−δ ceramics derived from oxalate coprecipitation: effects of Fe loading and sintering temperature

Ce0.9Gd0.1O2−δ powder was prepared by oxalate coprecipitation. Fe2O3 (0.5 at.%) was loaded into the powder through two approaches—mechanical mixing and wet chemical loading. The densification behavior, microstructure and electrical properties of the unloaded and Fe-loaded Ce0.9Gd0.1O2−δ ceramics, sintered at temperatures ranging from 1000 to 1550 °C for 5 h, were investigated. Both the Fe loading and the loading method exhibited a remarkable effect on the densification of Ce0.9Gd0.1O2−δ ceramics. The Fe loading by chemical way was more effective in promoting densification in the temperature range less than 1300 °C, as compared to that by mechanical mixing. However, the two different ways for Fe loading led to a very similar way in affecting the grain boundary (GB) conduction of the Ce0.9Gd0.1O2−δ ceramics. The GB conductance of the Fe-doped Ce0.9Gd0.1O2−δ ceramics experienced a rapid increase from 1100 to 1250 °C, reached a relatively broad maximum over 1250–1500 °C, and finally decreased at >1500 °C. This was completely different from the variation in the GB conduction of the unloaded samples with temperature, which decreased consistently with increasing sintering temperature. The Fe2O3 dopant exhibited the optimal scavenging effect in the temperature range of 1250–1500 °C, in which a higher total conductivity and a lower activation energy for the total conduction were achieved for Ce0.9Gd0.1O2−δ ceramics. Finally, the possible mechanisms related to the enhanced densification behavior and the improved GB conduction of the Ce0.9Gd0.1O2−δ ceramics due to Fe loading were discussed.