Synthesis Of Yttrium Aluminum Garnet Research Articles

Synthesis of yttrium aluminium garnet by the citrate gel process

We describe the synthesis of polycrystalline yttrium aluminium garnet (YAG) by the citrate gel process. The conditions for obtaining the pure phase have been determined and the YAG powders were characterized by X-ray diffraction, IR spectroscopy and transmission electron microscopy. YAG powders were obtained at significantly lower temperatures than by other conventional techniques. Moreover, the particle size of the powders prepared through this process is in the range 20–70 nm, depending on the thermal treatment. The lattice parameter of the YAG powders was also determined and we observed that the lattice parameter depends on the particle size. An explanation for this behaviour is provided.

Synthesis of yttrium aluminium garnet by the gel entrapment technique using hexamine

A novel technique has been developed for the preparation of yttrium aluminium garnet (YAG), represented by the chemical formula Y 3Al 5O 12, by achieving the homogeneous precipitation of the constituent metal hydroxides from the stoichiometric mixture of the metal nitrate solution by the addition of hexamethylene tetramine solution. Aluminium ions form a gel at pH 4, entrapping all the liquid, followed by the precipitation of yttrium ions at a higher pH. In spite of the sequential precipitation, the resultant mass is homogeneous because of the gel entrapment. Using this technique, singlephase YAG powder of high specific surface area (80 m 2 g −1) was obtained at 810 °C. Characterisation was done by thermogravimetry, differential thermal analysis, X-ray diffraction and scanning electron microscopy to ascertain the high quality of the product. The technique was subsequently used for the production of highpurity neodymium-doped YAG powder with excellent microhomogeneity on an increased batch size of 1 kg.

Synthesis of yttrium aluminium garnet by the glycerol route

Yttrium aluminium garnet (YAG), represented by the chemical formula Y 3Al 5O 12, was synthesised from the stoichiometric mixture of the metal nitrate solution by boiling with glycerol. For a fixed batch size, the glycerol amount was systematically varied to study its effect on the specific surface area and phase purity of the YAG powder. The quantity of glycerol was optimised to get the desired powder characteristics. Using this technique, single phase YAG powder of high specific surface area was obtained at 1000 °C. Characterisation was done by thermogravimetry (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), particle size analysis and by measuring the specific surface area, as well as the carbon content, at various stages, to ascertain the quality of the product.

Synthesis of Yttrium Aluminum Garnet from Yttrium and Aluminum Isobutyrate Precursors

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.

Synthesis of yttrium aluminum garnet by reverse strike precipitation

Yttrium aluminum garnet (YAG) powders were synthesized by normal and reverse strike precipitation from a mixed solution containing aluminum and yttrium nitrates. The precipitates were characterized by FTIR, DTA, and TGA techniques. The amorphous precipitates were crystallized under various atmospheres (air, argon, hydrogen) at different temperatures and the product analyzed by x-ray diffraction. Only reverse strike precipitation followed by crystallization in hydrogen consistently yielded phase pure YAG.

Synthesis of Yttrium Aluminum Garnet by the Glycothermal Method

The reaction of a stoichiometric mixture of aluminum isopropoxide and yttrium acetate in 1,4‐butanediol at 300°C yielded crystalline yttrium aluminum garnet having an approximate particle size of 30 nm. No other phases were detected. The use of ethylene glycol in place of 1,4‐butanediol afforded an amorphous product.