Synthesis of Yttrium Aluminum Garnet from Yttrium and Aluminum Isobutyrate Precursors

Abstract

Mixtures of yttrium and aluminum isobutyrates, M(O2CCHMe2)3= M(O2CiPr)3 (M = Y or Al), were examined as precursors for processing yttrium aluminum garnet (YAG, A15Y3O12). Both precursors were synthesized by reacting the respective metal with isobutyric acid. The individual compounds and the 5Al(O2CiPr)3:3Y(O2CiPr)3 YAG composition mixture were characterized by TGA, DTA, XRD, NMR, and FTIR. Pyrolytic decomposition of Al(O2CiPr)3 at temperatures ≤700°C produces amorphous A12O3, which partially crystallizes to α‐alumina at 840°C (by DTA), and finally to a‐alumina at 1120°C. The pyrolysis behavior of Y(O2CiPr)3 is quite different. Samples start to decompose at 260°C, producing mixtures of Y2O3 with minor quantities of a yttrium carbonate species. On further heating to 300°C, the amorphous Y2O3 crystallizes (bcc). The carbonate remains stable until ∼900°C, and phase‐pure, bcc Y2O3 is obtained only on heating to 1400°C. Mixtures of Al(O2CiPr)3 and Y(O2CiPr)3 provide a precursor to polycrystalline YAG. Rheologically useful solutions are obtained by dissolving a 5:3 mixture of Al(O2CiPr)3 and Y(O2CiPr)3 in THE Solvent removal provides bulk samples of the YAG precursor. The pyrolytic decomposition patterns of bulk samples of this YAG precursor were studied by heating to selected temperatures and characterizing by TGA, DTA, XRD, and FTIR. The crystallization behavior of the mixture is quite different from the constituent compounds. The precursor decomposes to an amorphous material on heating above 300°C. On continued heating (5°C/ min/air) this amorphous intermediate crystallizes (∼910°C) to phase‐pure YAG with a final ceramic yield of 26% at 1000°C. No other phases are observed to form over this temperature range.