COMPARISON OF SOLID-STATE AND SPRAY-PYROLYSIS SYNTHESIS OF YTTRIUM ALUMINATE POWDERS

The influence of precursor characteristics and synthesis conditions on the formation of yttrium aluminum garnet, Y3Al5O12(YAG), was investig ated using ''single-source'' precursors (cohydrolyzed yttrium and alum inum alkoxides and yttrium aluminum glycolates) and ''multiple-source' ' precursors (mixtures of metal nitrates and mixtures of separately hy drolyzed yttrium and aluminum alkoxides). Phase-pure YAG was formed on ly in the solid-state thermal decomposition experiments. The lack of f ormation of YAG in all the spray-pyrolysis experiments was ascribed to the short heating times and fast heating rates, which resulted in the formation of kinetic products. In the case of the metal nitrates, an additional factor that influenced product formation was the difference in thermal reactivity of the precursors. It was concluded that the fo rmation of complex metal oxide materials by conventional or aerosol ro utes is not necessarily achieved by the use of a chemically homogeneou s precursor, such as a single-source precursor. It also was necessary to ensure that the precursors and intermediates have similar thermal d ecomposition temperatures to avoid phase segregation in the initial st ages of thermal decomposition.