Characterization and thermal stability of Yb-doped ceria prepared by methods enabling control of the crystal morphology

Abstract

This study presents the results of investigations on the shape stability of crystalline ceria-based Ce_1−xYb_xO_2−(x/2) mixed oxides with increasing Yb content (x = 0 to 0.15). Cube-like and octahedral nanocrystals of the oxides were synthesized by a hydrothermal method. Additionally, nano-sized (∼5 nm) mixed oxides were prepared by precipitation with a water-in-oil (W/O) microemulsion method. Clearly visible differences in the aggregations and shapes of the formed particles were detected as a function of the Yb-content and morphology of the oxide crystals. As has been presented in this paper, individual crystallites of pure ceria and mixed Ce–Yb oxides with cube-like shapes were observed in TEM images. On the other hand, in the case of the octahedral crystals of oxides with the same nominal compositions, individual crystallites were observed only for pure CeO₂, in contrast to the Ce–Yb mixed oxides, where large agglomerates with octahedral shapes (built from smaller octahedral crystals of the mixed oxides) were observed. One of the most interesting observations connected with the formation of octahedral agglomerates of the mixed Ce–Yb oxides is the very similar orientations of the crystals which make up the large agglomerates.