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 synthes ized by reacting the respective metal with isobutyric acid. The indivi dual compounds and the 5Al(O(2)CiPr)(3):3Y(O(2)CiPr)(3) YAC compositio n mixture were characterized by TGA, DTA, XRD, NMR, and FTIR, Pyrolyti c decomposition of Al(O(2)CiPr)(3) at temperatures less than or equal to 700 degrees C produces amorphous Al2O3, which partially crystallize s to eta-alumina at 840 degrees C (by DTA), and finally to alpha-alumi na at 1120 degrees C, The pyrolysis behavior of Y(O(2)CiPr)(3) is quit e different, Samples start to decompose at 260 degrees C, producing mi xtures of Y2O3 with minor quantities of a yttrium carbonate species. O n further heating to 300 degrees C, the amorphous Y2O3 crystallizes (b cc), 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 t o 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 pyrol ytic 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 q uite different from the constituent compounds. The precursor decompose s to an amorphous material on heating above 300 degrees C, On continue d heating (5 degrees C/min/air) this amorphous intermediate crystalliz es (approximate to 910 degrees C) to phase-pure YAG with a final ceram ic yield of 26% at 1000 degrees C, No other phases are observed to for m over this temperature range.