Glycothermal synthesis of rare earth iron garnets
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Glycothermal synthesis of rare earth iron garnets Masashi Inoue,a) Toshihiro Nishikawa, and Tomoyuki Inui Department of Energy and Hydrocarbon Chemistry, Faculty of Engineering, Kyoto University, Yoshida, Kyoto 606-8501, Japan (Received 17 September 1997; accepted 2 January 1998)
The reactions of rare earth (RE) acetates with iron acetylacetonate in 1,4-butanediol at 300 ±C (glycothermal reaction) yielded two novel phases depending on the ionic size of the RE element: one was obtained for Er-Lu and the other for Tb and Dy. The former phase was hexagonal REFeO3 , while the latter phase has not been identified. The reaction of Y or Ho acetate yielded the mixture of these two phases. When the reactions were carried out in the presence of seed crystals of yttrium aluminum garnet (Y3 Al5 O12 ), these phases were not formed but RE iron garnet (RE3 Fe5 O12 ) grew on the seed, which suggests that spontaneous nucleation of RE iron garnet does not occur, but crystal growth proceeds easily under the glycothermal conditions. Hydrothermal reaction of the same starting materials yielded a mixture of Fe2 O3 and an amorphous RE phase.
I. INTRODUCTION
In the rare earth (RE) oxide-iron(3) oxide pseudobinary stable phase diagrams, there appear three phases: REFeO3 having the perovskite structure, RE3 Fe5 O12 having the garnet structure, and RE2 O3 ? 11 Fe2 O3 with a b-alumina type structure.1–4 The thermodynamical stability of these phases depends on the ionic size of the RE elements, and the garnet phase was reported to be stable for all the RE elements from Sm to Lu.1 Only a few works have dealt with the use of organic media in place of water for the hydrothermal method.5–7 We have explored the synthesis of inorganic materials in glycols at temperatures higher than the boiling point of the glycol (glycothermal reaction),8–18 and showed that binary oxides such as Y3 Al5 O12 (YAG, garnet),11,12 ZnAl2 O4 (spinel),13 and LiNbO3 (ilmenite structure)14 were directly formed when mixtures of the two starting materials (alkoxide, acetylacetonate or acetate) were heated in 1,4-butanediol (1,4-BG) at 300 ±C. In the present communication, the reactions of RE acetates with iron acetylacetonate under the glycothermal conditions will be reported.
solvent. The test tube was then set in a 300 ml autoclave, and an additional 20 ml of 1,4-BG was placed in the gap between the autoclave wall and the test tube. The autoclave was completely purged with nitrogen, heated to 300 ±C at a rate of 2.3 ±Cymin, and kept at that temperature for 2 h. After the assembly was cooled to room temperature, the resulting product was repeatedly washed with methanol and air dried. III. RESULTS
The results are summarized in Table I. The reactions of RE acetates with Fe(acac)3 yielded three different types of the product depending on the ionic size of the RE element (Fig. 1). For Nd–Gd, the
II. EXPERIMENTAL
Iron acetylacetonate [Fe(acac)3 ; Mitsuwa; 5.00 g, 14.2 mmol] and RE acetate (Wako Pure Chemical; 8.5 mmol) were place
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