A controlled co-precipitation technique was used to synthesize porous M2O3-doped (M = Gd, Sm) CeO2submicrometer particles with a narrow size distribution. Various precipitates in spherical or oval shape were obtained. The particles were made from a nitrate/urea solution by consideration of three aspects: the addition sequence of M-nitrate into Ce-nitrate/urea solution, the concentration ratio of M/Ce in the nitrate solutions, and the effect of seeding. Heterogeneous and secondary precipitations of fine particles and the cross-section of the particles were analyzed by electron microscopes (SEM and TEM) equipped with energy dispersive X-ray spectroscopy (EDS). The differential precipitation rate of Ce-and Me-nitrates in the urea solution, and the specific surface area of the synthesized powder calcined at temperatures up to 750 οC are also reported.

Keywords: Ceria, Precipitation, Microstructure, Powder.