Glycothermal Synthesis of Thermodynamically unstable Mixed Oxides

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This research has been carried out show that the glycothermal reaction, which this researcher has developed to synthesis nanocrystals of various metal oxides, can be applied for the synthesis of the metastable metal oxides. In 1997, the reaction mechanisms for the formation of hexagonal LnFeOィイD23ィエD2 by the reaction of iron acetylacetonate with rare earth acetates was examined in detail and the following points were found : (1) Reactivity of the starting material was controlled by the thermal stability of the ligand. (2) Higher reaction temperature increases the instability of hexagonal LnFeOィイD23ィエD2 and therefore increases the solubility of the phase resulting in an increase in the particle size of the product. (3) When the reaction was carried out in the presence of a small amount of garnet crystals, hexagonal LnFeOィイD23ィエD2 was not formed but rare earth iron garnet was formed. It was concluded that the prime factor for the formation of the metastable phase is the thermodynamical i … More nstability of the glycoxide intermediate, which gives large driving force for the formation of the final product. In 1998, the reaction of indium alkoxide with rare earth acetates, the reaction of aluminum isopropoxide with gallium acetylacetonate, and the reaction of titanium alkoxide with tetraethyl silicate were examined. The first reaction yielded the InィイD22ィエD2OィイD23-ィエD2LnィイD22ィエD2OィイD23ィエD2 solid solutions but metastable unidentified phases were also formed. The second reaction afforded large-surface area alumina-gallium oxide solid solutions having a crystal structure of metastable γ-alumina. The last reaction yielded a titania-silica solid solution having the anatase crystal structure. In this reaction, the sold solution with quite a large surface area was obtained by lowering the reaction temperature. During the course of the work mentioned above, this researcher also examined the reaction of cerium metal in 2-ethoxyethanol and found that the reaction afford a transparent colloidal solution of ultrafine ceria particles (2 nm diameter). One of the reason why this reaction afforded ceria having unique properties was that the oxidation of cerium metal gave quite a large driving force to the reaction. Less