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4 citations found for Sekikawa,

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The superstructure of titanium sesquisulfide, TiS1.46, is derived on the basis of 1 MV and 100 kV high-resolution electron microscope images. The crystal has monoclinic symmetry (pseudo-hexagonal) with lattice parameters a = 5-92, b = 10.3, c = 22.8 Å and [beta] = 90°. The space group is Cc. The metal vacancies are confined to every second metal layer and ordered within the layer. They are arranged in a stacking sequence of the 4C-type along the c axis. The sulfur atoms are in the 4H-type stacking sequence along the c axis.

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By combining 1 MeV high-voltage-high-resolution electron microscopy with convergent-beam electron diffraction (CBED), the crystal structure of a perovskite-related compound, Ca4YFe5O13, is determined. The crystal has orthorhombic symmetry with lattice parameters a = 5.46, b = 37.4 and c = 5.54 Å. The space group is determined to be centrosymmetric Pnma by selecting the point group from the CBED patterns. The structure images taken from two principle-axis directions, which are interpreted on the basis of the calculated images, reveal that the structure consists of a succession of the stacking of FeO6 octahedra (O layer) and FeO4 tetrahedra (T layer) and is represented by the stacking sequence of ...OTOOTOTOOTO... along the b axis repeated at intervals of 37.4 Å. It is shown that the Ca4YFe5O13 crystal structure can be described in terms of unit-cell-level twinning of Ca2Fe2O5.

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The crystal structure of bismuth tungstate, Bi2W2O9, has been examined by 1 MV high-resolution electron microscopy. The symmetry is orthorhombic with lattice parameters a = 5.43, b = 5.41 and c = 23.7 Å and space group Pna21. The point group is determined directly from the images in which each cation site is resolved. The structure is similar to that of conventional layered Bi compounds with respect to the Bi2O2 sheets normal to the c axis; however, the layer between the sheets is of a deformed ReO3 type. The strong chemical bonds between the Bi ions and the apex O atoms cause the rotation of the WO6 octahedron about the c axis. W ions are displaced antiparallel in the WO3 layer.

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