EuB<sub>6</sub>, GdB<sub>4</sub>及びTbB<sub>4</sub>単結晶の生成とその性質

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  • Preparation and Properties of EuB<sub>6</sub>, GdB<sub>4</sub> and TbB<sub>4</sub> Single Crystals
  • EuB6,GdB4 オヨビ TbB4タンケッショウ ノ セイセイ ト ソノ セ

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Preparation of single crystals of EuB6 (cubic system), GdB4 (tetragonal system) and TbB4 (tetragonal system) using the molten aluminum flux method in an argon atmosphere has been investigated. As-grown EuB6, GdB4 and TbB4 single crystals were used for chemical analysis, measurement of lattice constants, densities and Knoop-microhardness, and study of oxidation reaction kinetics in air temperature between 600°C and 1250°C. The optimum preparation conditions to obtain cubic EuB6, polyhedral GdB4 and polyhedral TbB4 single crystals are summarized as follows. The mixing atomic ratios of raw materials (B/Eu and Al/Eu) (B/Gd and Al/Gd) (B/Tb and Al/Tb): for EuB6, B/Eu=5.0 and Al/Eu=80.4-107.3; for GdB4, B/Gd=3.0-3.5 and Al/Gd=80.2-160.4; for TbB4, B/Tb=3.0-4.0 and Al/Tb=87.5-145.9. The heating temperature and time are 1500°C and 10h, respectively. Cubic single crystals of EuB6 composed of {100} faces, and needle and thick plate single crystals, each of which has well-developed {100} faces, were obtained. In the case of GdB4 and TbB4, polyhedral single crystals were obtained. The results of chemical analysis and measurements of lattice constants and densities (dm) determined are as follows:<br>EuB6: EuB5.83, a=4.1842±0.0009 (Å), dm=4.83±0.04g/cm3 GdB4: GdB3.86, a=7.146±0.001 (Å), c=4.046±0.001 (Å), dm=6.40±0.03g/cm3 TbB4: TbB3.99, a=7.119±0.002 (Å), c=4.027±0.002 (Å), dm=6.54±0.04g/cm3<br>Average values of Knoop-microhardness determined on {100} faces of EuB6 single crystals and that on {001} faces of GdB4 and TbB4 single crystals are as follows: EuB6: {100} ‹100› 2320-2470kg/mm2 {100} ‹110› 2200-2360kg/mm2 GdB4: {001} ‹100› 1760-1880kg/mm2 {001} ‹110› 1370-1540kg/mm2 TbB4: {001} ‹100› 1820-1960kg/mm2 {001} ‹110› 1390-1520kg/mm2<br>The oxidation reaction of EuB6 crystal began to proceed at about 640°C, giving on oxidation product of Eu(BO2)3. The oxidation reaction of GdB4 and TbB4 crystals began to proceed at 730°-750°C, and their oxidation products were found to be GdBO3 and TbBO3. In every case, noncrystalline B2O3 seemed to be formed during the oxidation reaction. The oxidation rates of EuB6, GdB4 and TbB4 were expressed by the oxidation rate equation, (dw)n=kt, and the calculated apparent activation energies of oxidation of EuB6, GdB4 and TbB4 crystals were 59.8±4.0kcal/mol, 144.4±4.2kcal/mol and 91.8±6.1kcal/mol, respectively.

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  • 窯業協會誌

    窯業協會誌 93 (1078), 301-310, 1985

    公益社団法人 日本セラミックス協会

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