Synthesis of yttrium aluminum garnet from yttrium and aluminum isobutyrate precursors

Mixtures of yttrium and aluminum isobutyrates, M(O(2)CCHMe(2))(3) = M(O(2)CiPr)(3) (M = Y or Al), were examined as precursors for processing yttrium aluminum garnet (YAG, Al5Y3O12), Both precursors were synthesized by reacting the respective metal with isobutyric acid. The individual compounds and the 5Al(O(2)CiPr)(3):3Y(O(2)CiPr)(3) YAC composition mixture were characterized by TGA, DTA, XRD, NMR, and FTIR, Pyrolytic decomposition of Al(O(2)CiPr)(3) at temperatures less than or equal to 700 degrees C produces amorphous Al2O3, which partially crystallizes to eta-alumina at 840 degrees C (by DTA), and finally to alpha-alumina at 1120 degrees C, The pyrolysis behavior of Y(O(2)CiPr)(3) is quite different, Samples start to decompose at 260 degrees C, producing mixtures of Y2O3 with minor quantities of a yttrium carbonate species. On further heating to 300 degrees C, the amorphous Y2O3 crystallizes (bcc), The carbonate remains stable until approximate to 900 degrees C, and phase-pure, bcc Y2O3 is obtained only on heating to 1400 degrees C. Mixtures of Al(O(2)CiPr)(3) and Y(O(2)CiPr)(3) provide a precursor to polycrystalline YAG, Rheologically useful solutions are obtained by dissolving a 5:3 mixture of Al(O(2)CiPr)(3) and Y(O(2)CiPr)(3) in THF, 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 degrees C, On continued heating (5 degrees C/min/air) this amorphous intermediate crystallizes (approximate to 910 degrees C) to phase-pure YAG with a final ceramic yield of 26% at 1000 degrees C, No other phases are observed to form over this temperature range.