The influence of annealing on grain growth in nanocrystalline CeO2 ceramics

Sol-gel technology was utilized to produce the nanocrystalline CeO2 ceramics in the form of bulk materials and coatings with thicknesses of up to 200 nm. After deposition, the CeO2 ceramics were composed of randomly oriented crystallites with a size of 5 nm. The grain size evolution during annealing depended on the coating thickness and the substrate nature. On non-oxidizing substrates the conversion of gel to ceramics was accompanied by the removal of water and organic species and followed by grain growth without formation of any evident texture. On substrates forming protective NiO and Cr2O3 films, the annealing resulted in the incorporation of CeO2 into the native oxides. When the CeO2 particles with a size smaller than 10 nm were incorporated, they started to dissolve at high temperatures and to saturate the network of grain boundaries of oxides with Ce ions. In contrast, the large particles did not change their size and remained inert inside the native oxides.