Formation and Solidification Points of Binary Compounds in the Ln<sub>2</sub>O<sub>3</sub>-Ga<sub>2</sub>O<sub>3</sub> System

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  • Ln<sub>2</sub>O<sub>3</sub>-Ga<sub>2</sub>O<sub>3</sub>系化合物の生成と凝固点
  • Ln2O3 Ga2O3ケイ カゴウブツ ノ セイセイ ト ギョウコテン

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Binary compounds in the systems Ln2O3-Ga2O3 (Ln=La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) were studied by solid state reaction and a quenching technique using a heliostat-type solar furnace. In the systems, the existence of four types of compounds was shown; garnet-type 3Ln2O3⋅5Ga2O3 (Ln=Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb), perovskite-type LnGaO3 (Ln=La, Pr, Nd), monoclinic 2Ln2O3⋅Ga2O3 (Ln=La, Pr, Nd, Sm, Eu, Gd) and orthorhombic 3Ln2O3⋅Ga2O3 (Ln=Sm, Eu, Gd, Dy, Ho, Er). These binary compounds, except LaGaO3, showed no phase transition during repeated heating and cooling cycles. In LaGaO3, a reversible orthorhombic-rhombohedral transition was found to occur at about 900°C, using a high-temperature X-ray diffractometer. Most of the binary compounds melted congruently. With increase in the ionic radius of Ln, the solidification point decreased for LnGaO3-type compounds and increased for 3Ln2O3⋅5Ga2O3-type and 2Ln2O3⋅Ga2O3-type compounds. Meanwhile, 3Ln2O3⋅Ga2O3-type compounds and 2Gd2O3⋅Ga2O3 were found to melt incongruently. The lattice parameters for the compounds showed shrinkage with the decrease of ionic radii of Ln. The refractive indices of the binary compounds were measured as follows: n=2.01-2.04 for 3Ln2O3⋅5Ga2O3, nγ=2.05-2.06, nα=2.04-2.05 for LnGaO3, nγ=1.95-2.01, nα=1.93-1.99 for 2 Ln2O3⋅Ga2O3, and nγ=2.01-2.05, nα=2.00-2.02 for 3Ln2O3⋅Ga2O3.

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