Sintering, microstructure and grain growth of Fe-doped Ce0.9Gd0.1O2−δ ceramics derived from oxalate coprecipitation

The precursor powder of Ce0.9Gd0.1O2−δ ceramics was prepared by oxalate coprecipitation. 0.1-3 at% (atomic percent) Fe2O3 was added into the powder via the conventional mixed-oxide method. The effects of doping level, and sintering temperature and time on the densification, microstructure and grain growth of Ce0.9Gd0.1O2−δ ceramics were investigated by means of dilatometry measurement, density testing and scanning electronic microscopy (SEM) observation. In the Fe content range used, the sintering temperature decreased consistently with increasing Fe level (from ∼1310 °C at 0.1 at% Fe to ∼1104 °C at 3 at% Fe). Small additions of Fe2O3 promoted the densification rate significantly. The densification rate reached a maximum at ∼1 at% Fe, then decreased with further increase in Fe content. For 0.5 at% Fe-doped Ce0.9Gd0.1O2−δ ceramic, over 97% relative density was complete during heating ramp from room temperature to 1350 °C at a heating rate of 10 °C/min, as compared to only ∼86% for the undoped ceramic. The Fe doping level was also found to have a remarkable influence on the grain growth behavior, which depended on sintering temperature. At lower temperatures (e.g., 1250 °C), a pinning effect on grain growth was found above 1 at% Fe additions. However, such a pinning effect became less important with increasing temperature. A slight increase in grain size was actually observed in the Fe-doped ceramic sintered at 1500 °C as the Fe content increased from 0.1 to 3 at%. The analysis based on the grain growth kinetics indicated that the undoped Ce0.9Gd0.1O2−δ ceramic followed a parabolic law for grain growth, while the 0.5 at% Fe-doped ceramic had a grain growth exponent of ∼4.