Synthesis of yttrium aluminum garnet by reverse strike precipitation
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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. I. INTRODUCTION Yttrium aluminum garnet (YAG, Y3AI5O12) single crystals are used as hosts for lasing media, especially for neodymium and chromium. There have been several efforts to make polycrystalline, translucent YAG by synthesizing the powder and using ceramic processing techniques to obtain fully dense cylinders. DeWith and his co-workers1 have synthesized YAG powders by two techniques. The first procedure involved mixing the yttrium and aluminum oxides in the correct proportions and heating the mixture to 'a high temperature' to obtain the garnet by interdiffusion. This was followed by grinding to obtain a powder for use in the sintering experiments. In the second procedure sulfate salts of yttrium and aluminum were mixed in an aqueous solution, at a pH of 3, the solution was spray dried, thermally decomposed, and calcined at 1300 °C to obtain a single phase YAG powder. Earlier work by Glushkova et al.2 consisted of the precipitation of an yttrium and aluminum hydroxide from a mixture of nitrate solutions in the correct ratio for YAG. The data reported show that YAG and other phases such as YAIO3 and Y2O3-2AI2O3 were formed when the hydroxide was calcined. They found that the YAG is formed at 1270 K and partially decomposes to YA103 at higher temperatures. They obtained high temperature diffractograms of the YAG precipitate at 1220, 1270, 1320, and 1420 K, in order to study phase changes at high temperature. At temperatures above 1220 K several unidentified peaks were observed, which disappeared when the samples were cooled to room temperature. It was proposed that the YAG structure is distorted above 1270 K. Takamori and David3 synthesized YAG by hydrothermal treatment of hydroxides precipitated from salt a
'Now with Sherritt Technologies, Sherritt Gordon Limited, Fort Saskatchewan, Alberta, Canada T8L 3W4.
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J. Mater. Res., Vol. 7, No. 3, Mar 1992
http://journals.cambridge.org
Downloaded: 11 Mar 2015
solutions. They mixed salts (chlorides or citrates) of yttrium and aluminum in the correct ratios at a pH of 3 and added NH 4 0H to obtain a precipitate at a pH of 9. The hydroxide precipitate (with ammonium salt impurities) was collected by freeze drying, and calcined at various temperatures ranging from 400 to 700 °C, to obtain an amorphous powder. This was used as a nutrient in a suspension in 350 ml of water, sealed in a platinum capsule, and heated at 100 MPa and 500-550 °C for 15 to 20 h. The hydrothermally produced amorphous powder had to be crystallized at temperatures between 800 and 950 °C. By
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