Formation of Ce 0.8Sm 0.2O 1.9 nanoparticles by urea-based low-temperature hydrothermal process

The synthesis and formation mechanism of the nano-sized Ce _0.8Sm _0.2O _1.9 particles prepared by a urea-based low-temperature hydrothermal process was investigated in this study. From ex situ X-ray diffraction and induced coupled plasma-atomic emission spectroscopy investigations, it was found that large quantities of cerium hydroxide co-precipitated with some samarium hydroxide at the initial stage of the hydrothermal process. The remaining Sm ³⁺ ions in the solutions were further hydrolyzed and deposited on the surface of the cerium hydroxide-rich precipitates to form a core-shell-like structure. During the hydrothermal process, the core-shell-like structure transformed to a single cubic fluorite phase which is due to the incorporation of the deposited samarium hydroxide into the cerium oxide-rich core. Further, the average grain size of the synthesized nanocrystalline Ce _0.8Sm _0.2O _1.9 was reduced with increasing the urea concentration in the solution. The density of the disk prepared with the synthesized Ce _0.8Sm _0.2O _1.9 powders was found to increase with a decrease in the grain size of Ce _0.8Sm _0.2O _1.9. The existence of SO ₄ ^2- anions in the SDC powders prepared at low-urea concentration may result in the SDC disks with low density due to their decomposition during sintering process.