Kenji Tsuda

Tohoku University, Japan

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Publications (92)163.5 Total impact

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    ABSTRACT: It is well known that BaTiO3 undergoes successive phase transformations from the cubic paraelectric phase to three ferroelectric phases: tetragonal, orthorhombic and rhombohedral ones. Coexistence of the displacive and order-disorder characters in the phase transformations of BaTiO3 was pointed out from many experiments and theories. However, local structures related to the order-disorder character were discovered neither in crystal structure analyses using neutron and X-ray diffraction nor by TEM observations. In the present study, the convergent-beam electron diffraction (CBED) method was applied to examine nanometer-scale local structures of BaTiO3. Rhombohedral nanostructures were observed in the orthorhombic and tetragonal phases of BaTiO3 using CBED [1]. It was found that the symmetry of the orthorhombic phase is formed as the average of two rhombohedral variants with different polarizations, and that of the tetragonal phase is formed as the average of four rhombohedral variants. These results indicate an order-disorder character in their phase transformations. Similar results were obtained in the ferroelectric orthorhombic phase of KNbO3 [2], while it was found that the ferroelectric tetragonal phase of PbTiO3 does not have such rhombohedral nanostructures. We also proposed a combined use of STEM and CBED methods (STEM-CBED method) to observe the nanostructures of polarizations [3]. Using the method, two-dimensional distribution of the rhombohedral nanostructures, or nanoscale fluctuations of the polarization clusters, were successfully visualized in the tetragonal phase of BaTiO3.
    No preview · Article · Aug 2014 · Acta Crystallographica Section A: Foundations and Advances
  • Kenji Tsuda · Michiyoshi Tanaka
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    ABSTRACT: Recently, nanometer-scale local structures with rhombohedral symmetry were discovered in BaTiO3 and KNbO3 using convergent-beam electron diffraction (CBED). In the present study, it has been examined using the CBED method whether such local structures exist in PbTiO3. It has been found that the symmetries of CBED patterns of the ferroelectric tetragonal phase of PbTiO3 agree with those expected from the tetragonal structure reported by X-ray crystal structure analysis. That is, the present study has revealed that such nanostructures as observed in BaTiO3 and KNbO3 do not exist in the tetragonal phase of PbTiO3. (c) 2013 The Japan Society of Applied Physics
    No preview · Article · Oct 2013 · Applied Physics Express
  • Kenji Tsuda · Akira Yasuhara · Michiyoshi Tanaka
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    ABSTRACT: Nanometer-sized structures with rhombohedral symmetry were discovered in the tetragonal and orthorhombic phases of perovskite-type ferroelectric BaTiO3, using convergent-beam electron diffraction [K. Tsuda, R. Sano, and M. Tanaka, Phys. Rev. B 86, 214106 (2012)]. The existence of rhombohedral nanostructures indicates an order-disorder character in their phase transformations. In the present study, spatial distributions of the nanostructures have been examined by the combined use of the scanning transmission electron microscopy and convergent-beam electron diffraction methods. Two-dimensional distributions of polarizations of the rhombohedral nanostructures have been visualized in the tetragonal phase of BaTiO3.
    No preview · Article · Aug 2013 · Applied Physics Letters
  • Kenji Tsuda · Rikiya Sano · Michiyoshi Tanaka
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    ABSTRACT: Symmetries of nanometer-scale local structures in the rhombohedral and orthorhombic phases of potassium niobate (KNbO3) have been examined using convergent-beam electron diffraction. Nanometer-size local structures with rhombohedral symmetry have been discovered in the orthorhombic phase of KNbO3. It has been found that the structure of the orthorhombic phase of KNbO3 is formed as an average of two variants with rhombohedral symmetry. This fact indicates that the phase transformation between the orthorhombic and rhombohedral phases has an order-disorder character. The result is analogous to the case of BaTiO3, which we already reported [Tsuda et al., Phys. Rev. B 86, 214106 (2012)].
    No preview · Article · Feb 2013 · Applied Physics Letters
  • Kenji Tsuda · Rikiya Sano · Michiyoshi Tanaka
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    ABSTRACT: The symmetries of the rhombohedral, orthorhombic, and tetragonal phases of barium titanate (BaTiO3) are investigated using convergent-beam electron diffraction. Nanometer-sized local structures with rhombohedral symmetry are observed in both the orthorhombic and tetragonal phases. This indicates that an order-disorder character exists in phase transformations of BaTiO3. The nanostructures in these phases are discussed in terms of an order-disorder model with off-centered Ti in the <111> directions.
    No preview · Article · Dec 2012 · Physical review. B, Condensed matter
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    R Theissmann · H Fuess · K Tsuda
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    ABSTRACT: Structural parameters of hematite (α-Fe(2)O(3)), including the valence electron distribution, were investigated using convergent beam electron diffraction (CBED) in the canted antiferromagnetic phase at room temperature and in the collinear antiferromagnetic phase at 90K. The refined charge density maps are interpreted as a direct result of electron-electron interaction in a correlated system. A negative deformation density was observed as a consequence of closed shell interaction. Positive deformation densities are interpreted as a shift of electron density to antibinding molecular orbitals. Following this interpretation, the collinear antiferromagnetic phase shows the characteristic of a Mott-Hubbard type insulator whereas the high temperature canted antiferromagnetic phase shows the characteristic of a charge transfer insulator. The break of the threefold symmetry in the canted antiferromagnetic phase was correlated to the presence of oxygen-oxygen bonding, which is caused by a shift of spin polarized charge density from iron 3d-orbitals to the oxygen ions. We propose a triangular magnetic coupling in the oxygen planes causing a frustrated triangular spin arrangement with all spins lying in the oxygen planes. This frustrated arrangement polarizes the super-exchange between iron ions and causes the spins located at the iron ions to orient in the same plane, perpendicular to the threefold axis.
    Full-text · Article · May 2012 · Ultramicroscopy
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    Michiyoshi Tanaka · Kenji Tsuda
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    ABSTRACT: This paper reviews the convergent-beam electron diffraction (CBED) technique. Point- and space-group determination methods of ordinary crystals are described, along with an example of the determination method for Sr₃Ru₂O₇. The symmetry determination of one-dimensionally incommensurate crystals and quasicrystals is explained. The large-angle CBED technique, which is indispensable for lattice defect and lattice strain analysis, is also described. A real procedure for lattice strain analysis is provided, using an example of a multilayer Si₁-xGe(x)/Si material. A nanometer-scale crystal structure refinement method and charge density and crystal potential determination method by CBED are briefly described.
    Preview · Article · Aug 2011 · Journal of electron microscopy
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    K. Tsuda · R. Sano · M. Tanaka

    Preview · Article · Aug 2011 · Acta Crystallographica Section A Foundations of Crystallography
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    ABSTRACT: The structure of AgNbO3 is determined by synchrotron and powder neutron diffraction, convergent-beam electron diffraction, SAED, and DFT calculations.
    No preview · Article · Jun 2011 · ChemInform
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    ABSTRACT: Crystal structure of ferroelectric silver niobate AgNbO3 was determined (Pmc21) by convergent beam electron, electron, neutron, and synchrotron diffraction techniques and first-principles calculations. The atomic displacements along the c axis in Pmc21 AgNbO3 are responsible for the spontaneous polarization, ferroelectricity, and the paraelectric-ferroelectric phase transition.
    Full-text · Article · Mar 2011 · Chemistry of Materials
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    ABSTRACT: High-angle annular dark-field (HAADF) images of an Al72Ni20Co8 decagonal quasicrystal and monoclinic Al13Fe4 and τ2-inflated Al13Co4 approximants have been presented. We found that a 2 nm atom cluster of Al72Ni20Co8, which have been believed to be tenfold so far, has no tenfold symmetry. A new structural model of Al72Ni20Co8 has been constructed on the basis of the HAADF images and the structure of monoclinic Al13Fe4 approximant. We have found that the monoclinic Al13Fe4 and τ2-inflated Al13Co4 approximants are composed of the same basic structure of a pentagonal atom cluster with an edge length of 0.47 nm. We have also found that a fivefold atom-cluster with a 2 nm diameter exists in τ2-Al13Co4, which was observed in decagonal quasicrystals of Al-Ni-Fe, Al-Ni-Co, Al-Cu-Co and Al-Co by high-resolution electron microscopy. A structural model of τ2-inflated Al13Co4 is constructed on the basis of the convergent-beam electron diffraction symmetry, HAADF images and the structure of monoclinic Al13Fe4.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    Roland Schierholz · Kenji Tsuda · Hartmut Fuess

    Preview · Article · Aug 2010 · Acta Crystallographica Section A Foundations of Crystallography
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    Roland Schierholz · Kenji Tsuda · Hartmut Fuess

    Preview · Article · Aug 2010 · Acta Crystallographica Section A Foundations of Crystallography
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    ABSTRACT: We introduce a new method to measure structure factors from parallel beam electron diffraction (PBED) patterns. Bloch wave refinement routines were developed which can minimise the difference between simulated and experimental Bragg intensities via variation of structure factors, Debye parameters, specimen thickness and -orientation. Due to plane wave illumination, the PBED refinement is highly efficient not only in computational respect, but also concerning the experimental effort since energy filtering is shown to have no significant effect on the refinement results. The PBED method was applied to simulated GaAs diffraction patterns to derive systematic errors and rules for the identification of plausible refinement results. The evaluation of experimental GaAs PBED patterns yields a 200 X-ray structure factor of -6.33±0.14. Additionally, we obtained -6.35±0.13 from two-dimensional convergent beam electron diffraction refinements. Both results confirm density functional theory calculations published by Rosenauer et al. and indicate the inaccuracy of isolated atom scattering data, which is crucial e.g. for the composition evaluation by lattice fringe analysis.
    Full-text · Article · Feb 2010 · Journal of Physics Conference Series
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    ABSTRACT: We present a new method to measure structure factors from electron spot diffraction patterns recorded under almost parallel illumination in transmission electron microscopes. Bloch wave refinement routines have been developed to refine the crystal thickness, its orientation and structure factors by comparison of experimentally recorded and calculated intensities. Our method requires a modicum of computational effort, making it suitable for contemporary personal computers. Frozen lattice and Bloch wave simulations of GaAs diffraction patterns are used to derive optimised experimental conditions. Systematic errors are estimated from the application of the method to simulated diffraction patterns and rules for the recognition of physically reasonable initial refinement conditions are derived. The method is applied to the measurement of the 200 structure factor for GaAs. We found that the influence of inelastically scattered electrons is negligible. Additionally, we measured the 200 structure factor from zero loss filtered two-dimensional convergent beam electron diffraction patterns. The precision of both methods is found to be comparable and the results agree well with each other. A deviation of more than 20% from isolated atom scattering data is observed, whereas close agreement is found with structure factors obtained from density functional theory [A. Rosenauer, M. Schowalter, F. Glas, D. Lamoen, Phys. Rev. B 72 (2005), 085326-1], which account for the redistribution of electrons due to chemical bonding via modified atomic scattering amplitudes.
    Full-text · Article · Apr 2009 · Ultramicroscopy
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    ABSTRACT: A transmission electron microscopy (TEM) study on the real internal structure of synthetic hematite sample was conducted. The samples were prepared by dissolving ferric chloride hexahydrate (FeCl3 · 6H2O) in water at room temperature, resulting in a clear 0.02 M solution of yellow color. The results show that the ideal hematite lattice can be seen at the lower right corner of the image, the rest of the image shows a deviating periodicity. A convergent-beam electron diffraction (CBED) pattern of natural hematite shows remarkable differences compared to those of the synthetic samples. The symmetry of the synthetic particle of own production matches the quality of the natural sample in the area near the sample edge, which corresponds to the lower right of the image.
    No preview · Article · Mar 2009 · Journal of Materials Science
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    ABSTRACT: Construction of structural phase diagram of LaGa1-xMg xO3-δ has been attempted by using synchrotron X-ray diffraction, high temperature X-ray diffraction, dilatometry and differential scanning calorimetry. Existence of long-period anti-phase domain structure(LPAPDS) observed in the specimens with x larger than 0.10 by using electron diffraction analysis was considered for the phase diagram construction. Existence of four phases has been proposed and their phase relationship has been evaluated. For the specimen with x = 0.00, orthorhombic phase free from LPAPDS and rhombohedral phase without LPAPDS were detected. In LaGa 1-xMgxO3-δ with x larger than 0.10, orthorhombic phase and rhombohedral phase with LPAPDS were proposed. It was suggested that the slow kinetics of the phase transition from orthorhombic phase with LPAPDS to rhombohedral with LPAPDS was the origin of region, where mixture of orthorhombic phase and rhombohedral phase was observed. Existence of two-phase region, where phase free from LPAPDS and one with LPAPDS coexist, has been clarified. The compositional region, where x is around 0.05, is revealed to be the two-phase region from room temperature to 800°C.
    No preview · Article · Feb 2009
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    ABSTRACT: The crystal structure of the β-pyrochlore oxide superconductor KOs2O6 is re-examined. A single-crystal X-ray diffraction (XRD) analysis at room temperature first revealed that the compound crystallizes in a cubic structure with the centrosymmetric space group , as in conventional pyrochlore oxides. Later, however, Schuck et al. claimed a different non-centrosymmetric structure based on their single-crystal XRD analysis. To unambiguously determine the true crystal structure of KOs2O6, we carried out high-resolution synchrotron powder X-ray and convergent-beam electron diffraction measurements at room temperature. The space group was determined with high reliability to be centrosymmetric , not . This confirms the importance of the K atom location in a high-symmetry site, which causes unusually large rattling of the K atom.
    Preview · Article · Jan 2009 · Solid State Communications
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    ABSTRACT: X-ray diffraction measurements of Al2(WO4)3 were carried out under various temperatures from 123 K to 373 K. Diffraction patterns above 273 K and below 253 K could be successfully explained as orthorhombic Pbcn (No. 60) and monoclinic P21/n (No. 14) with superstructure, respectively, which were in agreement with the results of convergent-beam electron diffraction. Thermal expansion of low-temperature monoclinic phase and slight shrinkage of high-temperature orthorhombic phase were observed from the temperature dependence of lattice constants and molar volume, showing agreement with the result of dilatometry. It is revealed that abrupt expansion of Al2(WO4)3 at the structural phase transition is attributed to an abrupt increase of the c-axis, which is parallel to the 21 screw axis and perpendicular to the n-glide plane. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    No preview · Article · Nov 2008 · physica status solidi (b)
  • Yoichiro Ogata · Kenji Tsuda · Michiyoshi Tanaka
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    ABSTRACT: A structure-analysis method using convergent-beam electron diffraction (CBED) developed by Tsuda et al. [Tsuda & Tanaka (1999), Acta Cryst. A55, 939-954; Tsuda, Ogata, Takagi, Hashimoto & Tanaka (2002), Acta Cryst. A58, 514-525] has been applied to the determination of the electrostatic potential and electron density of crystalline silicon. CBED patterns recorded at nine different incidences are simultaneously used to improve the accuracy of the refinement. The Debye-Waller factor and low-order structure factors of silicon have been successfully refined only using CBED data. The electrostatic potential and electron-density distribution have been reconstructed from the refined parameters. The latter clearly shows the bonding electrons between the nearest neighbor atoms. The obtained results are compared with the results of other CBED and recent X-ray diffraction experiments. The influence of the number of refined low-order structure factors on the electron density is discussed. The effect of the reduction of experimental data points on the accuracy of the refined parameters is also examined.
    No preview · Article · Sep 2008 · Acta Crystallographica Section A Foundations of Crystallography

Publication Stats

1k Citations
163.50 Total Impact Points

Institutions

  • 1993-2013
    • Tohoku University
      • • Institute of Multidisciplinary Research for Advanced Materials (IMRAM)
      • • Institute for Materials Research
      Japan
  • 2011
    • Tokyo Institute of Technology
      • Department of Materials Science and Engineering
      Edo, Tokyo, Japan
  • 2001
    • Nihon University
      • College of Humanities and Sciences
      Edo, Tōkyō, Japan
  • 2000
    • The University of Tokyo
      白山, Tōkyō, Japan
  • 1989
    • Aoyama Gakuin University
      Edo, Tokyo, Japan