The preparation of aluminum mixed metal oxides using different soft chemistry synthesis methods has been also performed. We have developed new modified sol-gel methods to prepare yttrium aluminum garnet. Nanocrystalline yttrium aluminum garnet (YAG, Y3Al5O12) and Ce-doped YAG ceramics were synthesized by two ‘soft chemistry’ sol-gel processes using (i) mixtures of inorganic salts or oxides and (ii) mixtures of alkoxides of the respective elements.
In the first approach, the metal ions, generated by dissolving metal oxides or nitrates in acetic acid and/or water were complexed by ethylene glycol to obtain the precursor for YAG. The formation of mixed-element acetate-glycolate frameworks in the gels could be inferred on comparing the thermogravimetric and IR spectral features of YAG gels with analogously prepared gels of individual components. In the case of alkoxide route, monolithic gels were obtained by hydrolysis and condensation of a compositional mixture of aluminium, yttrium and cerium alkoxides in an isopropanol solution. The molecular level mixing and the tendency of partially hydrolyzed alkoxide species to form extended networks facilitates the structure evolution thereby lowering the crystallization temperature. The XRD patterns of the ceramic sintered at 700 °C were identical with the stoichiometric YAG composition which is the lowest temperature reported for the synthesis of crystalline and phase pure Y3Al5O12 while well-developed YAG phases in the non-alkoxide synthesis were obtained only at 1000 °C. Cerium doped YAG powders were synthesised by using [Ce3(OBut)9(ButOH)2] or [NH4]2[Ce(NO3)6] as dopants.
The sol-gel method based on metal chelates with 1,2–ethanediol in aqueous media has been developed to prepare multimetallic oxides Y3Al5O12 (YAG), Y3Sc2Al1Ga2O12 (YSAGG–3212), Y3Sc1Al3Ga1O12 (YSAGG–3131), Y3Sc2Al3O12 (YSAG), Y3Al3Ga2O12 (YAGG), Y3Sc2.5Ga2.5O12 (YSGG) having complicated both chemical composition and garnet crystal structure. The XRD patterns of the ceramic materials sintered at 1000 °C showed the formation of monophasic garnet phase.