09:45 〜 10:00
[SMP38-04] The effect of silicon incorporation on the crystal structure of katoite Ca3Al2(O4H4)3
キーワード：katoite、hydrogrossular、single-crystal x-ray diffraction、EPMA、Raman spectroscopy
Single crystals of katoite Ca3Al2(SiO4)3-x(H4O4)x were hydrothermally synthesized from a mixture of CaO, metal Al, and amorphous SiO2 with a molar ratio of 3:1:1 at 250 oC for 4 days. Single crystals of approximately 20 mm in diameter exhibit a rhombic dodecahedron habit with well-developed 12 equivalent {1 1 0} crystal faces. The crystal structures of katoite have been investigated by single-crystal x-ray diffraction method, electron microprobe analysis, and Raman spectroscopic technique. The crystal structures of katoite obtained have cubic space group Ia-3d with a = 12.490(4) Å, V = 1948.4(2) Å3, and with a = 12.546(3) Å, V = 1974.8(2) Å3, respectively. The full matrix least-squares refinements of these katoites converged to R1 = 0.030, wR2 = 0.090 for 176 unique reflections and R1 = 0.032, wR2 = 0.095 for 160 unique reflections. The chemical formula refined from the site occupancy parameters of Si were Ca3Al2(SiO4)0.26(2)(OH)10.96(2) and Ca3Al2(SiO4)0.17(3)(OH)11.32(3), respectively. The EPMA data for these katoites supported the incorporation of Si into the structures and showed a deficiency of Ca in the dodecahedral site. The volumes of tetrahedral site were decreased with the Si incorporation into the tetrahedral site. Since one edge of the tetrahedra is shared with an adjacent dodecahedron, the volumes of CaO6 dodecahedra were also decreased with the Si incorporation. The resulting contractions of the coordination polyhedra led to the decrease of unit cell volume. The coordination volumes of the tetrahedra and dodecahedra lie on the straight line between grossular and hydrogrossular. The coordination volumes and rotation of AlO6 octahedra, on the other hand, almost remained unchanged with the Si incorporation. The OH stretching of the Raman spectrum was slightly shifted to lower energy compared to that in the hydrogrossular, which is ascribed to the weakening of the hydrogen bonding interactions.