Phase formation in yttrium aluminum garnet powders synthesized by chemical methods

Abstract

Yttrium aluminum garnet (YAG) powders were synthesized by precipitation of hydroxides using three types of precursors: nitrates (nitrate process), isopropoxides (alkoxide process), and isopropoxides chelated with ethyl acetoacetate (modified alkoxide process). The phase development in the powders during heat treatments was investigated with DTA and XRD. An intermediate hexagonal YAlO(3) (YAH) phase was formed at 800 degrees C in all powders regardless of the synthesis processes, but its complete transformation to YAG at higher temperatures (greater than or equal to 1000 degrees C) occurred only in the powders prepared by the nitrate and modified alkoxide processes. The alkoxide process led to the largest deviation from the bulk composition, producing a single phase of YAH that transformed into YAG plus a stable YAM (Y(4)Al(2)O(9)) phase. The modified alkoxide process led to the most homogeneous bulk composition, resulting in the least amount of YAH in the powder. The poor chemical homogeneity in the powders prepared by the nitrate and alkoxide processes was attributed to the segregation of the hydroxides and to the presence of the double alkoxide, respectively. (C) 2000 Kluwer Academic Publishers.