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6. Structures of Ca5(VO4)3Cl and Ca4.78(1)Na0.22(PO4)3Cl0.78: positions of channel anions and repulsion on the anion in apatite‐type compounds.

Author

Matsuura, Mimiko and Okudera, Hiroki

Subjects
*CHLORIDE channels, *ELECTRON density, *ANIONS, *ELECTRON distribution, *CALCIUM ions, *SINGLE crystals, *CALCIUM compounds
Abstract

Single crystal specimens of apatite‐type compounds Ca5(VO4)3Cl and Ca4.78 (1)Na0.22(PO4)3Cl0.78 were prepared with a flux‐growth technique and their structures were examined with single‐crystal X‐ray diffraction. The anion channel is defined by a face‐sharing array of nearly regular Ca octahedra, which run along c, together with flat O3 trigonal antiprisms that are concentric with the Ca octahedra and highly oblate in [001]. The position of the channel anion in Ca5(VO4)3Cl is split into two at [0, 0, ±0.1691 (6)] with half occupancies. Dynamic disorder among these two positions is suggested from a saddle‐shaped electron density distribution through the Ca regular triangle, i.e. the shared face of the Ca octahedra at z = ¼. The position of Cl− was too close to Ca2+ under bond‐valence consideration. This is due to repulsion on Cl− from the flat O3 trigonal antiprism which is located at z = 0, namely, in between pairs of split Cl site positions. Ca4.78 (1)Na0.22(PO4)3Cl0.78 crystallizes as a disordered hexagonal structure in which the crystallographic pattern is not an intermediate state but a projection of two distinct halves of the monoclinic pattern [doubled in b; Mackie, Elliot & Young (1972). Acta Cryst. B28, 1840–1848] in one hexagonal cell. In spite of quite different environments, the bond‐valence sums for Cl− in these structures are large and similar to each other. The repulsion between O2− and Cl− and a demand for keeping Ca2+ and Cl− apart are balanced at the positions where bond‐valence sums for Cl− are around 1.2. [ABSTRACT FROM AUTHOR]

Published
2022
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14. The shock behavior of water in hydrous amorphous silica materials

Author

Arasuna, Akane, Okuno, Masayuki, Okudera, Hiroki, and Mashimo, Tsutomu

Subjects
water molecule, opal, amorphous silica, silica gel, silanol
Abstract

平成27年度衝撃波シンポジウム (2016年3月7日-9日. 熊本大学 黒髪南地区）熊本市, 熊本県, Symposium on Shock Waves in Japan, FY2015 (March 7-9, 2016. Kumamoto University), Kurokami Chuo-ku, Kumamoto, Japan, 資料番号: SA6000049137, レポート番号: P-25

Published
2016

15. Conduction Pathway of Oxide Ions in Rare-Earth Silicate Oxyapatites

Author

Okudera, Hiroki, Masubuchi, Yuuji, and Kikkawa, Shinichi

Subjects
アパタイト
Abstract

Apatite-type RE9.33(SiO4)6O2 rare-earth silicate compounds are of great interest for their oxide ion conductivity at moderate temperatures. Crystallographic space group and structural parameters of La/Nd9.33(SiO4)6O2 were investigated based on single-crystal X-ray diffraction data at room temperature for La9.33(SiO4)6O2 and at various temperatures from 150 to 900 K for Nd9.33(SiO4)6O2. Based on the most accurate diffraction data to date, these compounds have an apatite prototype structure (space group P63/m) with no symmetry lowering, site splitting nor interstitial oxide ion in the structure. Most striking feature of the structure is large anisotropy in thermal motions of the oxide ion at the anion channel site. Even at room temperature, the mean-square displacement of the channel oxide ion in La9.33(SiO4)6O2 is 16 times larger in [001] than those normal to the direction. Not striking but important point is that there is no sign of interstitial oxide ion which had been proposed as a charge carrier in La9.33(SiO4)6O2 and related compounds. These findings imply straight migration of oxide ion inside the channel as a primary mechanism of oxide-ion conductivity in these compounds. Size and shape of the anion channel might be a key to achieve high oxide-ion conductivity in these compounds.

Published
2011

17. Structure of russellite (Bi2WO6): origin of ferroelectricity and the effect of the stereoactive lone electron pair on the structure.

Author

Okudera, Hiroki, Sakai, Yuka, Yamagata, Kentaro, and Takeda, Hiroaki

Subjects
*BISMUTH compounds, *FERROELECTRICITY, *ELECTRON pairs
Abstract

The structure of the low‐temperature polar (orthorhombic) phase of russellite (Bi2WO6) was examined on artificial specimens with precise single‐crystal X‐ray diffraction experiments. The final atomic arrangement thus obtained was identical to that reported by Knight [Miner. Mag. (1992), 56, 399–409] with powder neutron diffraction. The residual density attributable to a stereochemically‐active lone pair of electrons of bismuth was prominent at approximately the centre of a larger cap of BiO8 square antiprisms, that is on the line from the Bi sites to an adjacent WO42− slab along the b‐axis direction. Quite uneven Bi—O distances and the formation of a vacant coordination hemisphere (within 3 Å) should, therefore, be ascribed to the strong demand of bismuth to form shorter Bi—O bonds to use up its electrostatic charge within its coordination environment. The shift of bismuth along −c propagates via the correlated shift of the W site and these cooperative shifts cause ferroelectricity in the compound. This propagation was easily effected by the intrusion of molecules such as acetone into the structure. [ABSTRACT FROM AUTHOR]

Published
2018
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21. Synthesis of novel CoCx@C nanoparticles

Author

Chen, Liliang, primary, Mashimo, Tsutomu, additional, Iwamoto, Chihiro, additional, Okudera, Hiroki, additional, Omurzak, Emil, additional, Ganapathy, Hullathy Subban, additional, Ihara, Hirotaka, additional, Zhang, Jidong, additional, Abdullaeva, Zhypargul, additional, Takebe, Shintaro, additional, and Yoshiasa, Akira, additional

Published
2013
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25. Wurtzite-type ZnS nanoparticles by pulsed electric discharge

Author

Omurzak, Emil, primary, Mashimo, Tsutomu, additional, Sulaimankulova, Saadat, additional, Takebe, Shintaro, additional, Chen, Liliang, additional, Abdullaeva, Zhypargul, additional, Iwamoto, Chihiro, additional, Oishi, Yudai, additional, Ihara, Hirotaka, additional, Okudera, Hiroki, additional, and Yoshiasa, Akira, additional

Published
2011
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