2007 Volume 15 Pages 51-57
The synthesis of CeO2/ZrO2 core/shell nanocrystals (NCs), which are CeO2 NCs overcoated by a thin ZrO2 layer, has been studied together with CeO2, Sm2O3 and Gd2O3 doped CeO2 and ZrO2 NCs by a hot-surfactant colloidal method. Colloidal oleylamine solutions of the CeO2, and doped CeO2 NCs with an approximately 2.0 nm diameter and ZrO2 NCs with a 2.5～3.5 nm diameter were respectively synthesized by the thermolysis of metallic acetylacetonates and the nonhydrolytic sol-gel reaction of Zr[OCH(CH3)2]4 and ZrCl4. The CeO2/ZrO2 core/shell NCs have been successfully synthesized by the addition of CeO2 NCs as seed crystals to the ZrO2 source solution and its reaction at 300□. The core/shell nanostructure, which consists of a 2.4 nm diameter CeO2-core and 1.2 nm thick ZrO2-shell, was determined by its XRD and HREM results.
The synthesis of Y2O3-stabilized zirconia was attempted by the following procedure: Zirconium isopropoxide, zirconium chloride and yttrium isopropoxide were dissolved in oleylamine at 60□ for a hour. The Y-concentration of the starting solution were varied as 10, 20, 30 at% and then the solutions were heated at 340□ for 2 h under Ar atmosphere. The products were transparent and colloidal solutions. Average particle sizes of the product powders extracted from the solutions were ranged in 2.0～2.6nm diameter. The lattice parameter, calculated from XRD patterns, increased with the analytical concentration of Y in the obtained powders. Based on these results, it was concluded that the YSZ nanocrystals were successfully synthesized. The grain growth behavior of the obtained YSZ nanocrystals was also investigated. Distinct grain growth was not observed below 800□; steep grain growth occurred above 850□. The low temperature sintering at 600□ of the YSZ nanocrystals using SPS technique was attempted, however, the resulting compact showed 69% of the theoretical density. Further study was needed in order to obtain the high density sample with several nm in grain size.