Kenji Tsuda

Tohoku University, Japan

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Publications (79)132.41 Total impact

  • 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
    Applied Physics Express 10/2013; 6(10):101501. DOI:10.7567/APEX.6.101501 · 2.57 Impact Factor
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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.
    Applied Physics Letters 08/2013; 103(8). DOI:10.1063/1.4819221 · 3.52 Impact Factor
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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)].
    Applied Physics Letters 02/2013; 102(5). DOI:10.1063/1.4791679 · 3.52 Impact Factor
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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.
    Physical review. B, Condensed matter 12/2012; DOI:10.1103/PhysRevB.86.214106 · 3.66 Impact Factor
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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.
    Ultramicroscopy 05/2012; 120:1-9. DOI:10.1016/j.ultramic.2012.04.006 · 2.75 Impact Factor
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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.
    Journal of electron microscopy 08/2011; 60 Suppl 1(3):S245-67. DOI:10.1093/jmicro/dfr038 · 1.63 Impact Factor
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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.
    ChemInform 06/2011; 42(25):no-no. DOI:10.1002/chin.201125006
  • Chemistry of Materials 03/2011; 23(7). DOI:10.1021/cm103389q · 8.54 Impact Factor
  • MRS Online Proceeding Library 01/2011; 553. DOI:10.1557/PROC-553-177
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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.
    Journal of Physics Conference Series 02/2010; 209(1):012025. DOI:10.1088/1742-6596/209/1/012025
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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.
    Ultramicroscopy 04/2009; 109(7):802-14. DOI:10.1016/j.ultramic.2009.03.029 · 2.75 Impact Factor
  • Journal of Materials Science 01/2009; 44(5):1421-1424. DOI:10.1007/s10853-007-1718-3 · 2.31 Impact Factor
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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.
    Solid State Communications 01/2009; 149(1-2-149):31-34. DOI:10.1016/j.ssc.2008.10.029 · 1.70 Impact Factor
  • 01/2009; 77(2):169-177. DOI:10.5796/electrochemistry.77.169
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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)
    physica status solidi (b) 11/2008; 245(11):2504-2508. DOI:10.1002/pssb.200880258 · 1.61 Impact Factor
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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.
    Acta Crystallographica Section A Foundations of Crystallography 09/2008; 64(Pt 5):587-97. DOI:10.1107/S0108767308021338 · 2.07 Impact Factor
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    ABSTRACT: This work focuses on the crystal symmetry of morphotropic PbZrxTi1-xO3 (PZT). The crystal symmetry is investigated within single domains of &ap;30 100nm width by convergent beam electron diffraction (CBED). The composition PbZr0.54Ti0.46O3 was chosen for experiments at room temperature and &ap;300°C . The observed zone axis symmetry at room temperature was a (1¯10) mirror in some domains whereas symmetry was broken in neighboring domains. Therefore the highest crystal symmetry that can be attributed with certainty to the probed volume is monoclinic. The local symmetry of single cells might be lower due to disordered displacements of the cations. At &ap;300°C the zone axis symmetry had changed to a (100)pc mirror that only occurs in the tetragonal phase of PZT.
    Physical review. B, Condensed matter 07/2008; 78(2). DOI:10.1103/PhysRevB.78.024118 · 3.66 Impact Factor
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    ABSTRACT: The space-group symmetries of a negative thermal expansion material Al2(WO4)3 that undergoes a structural phase transformation at Tc=-22 °C have been investigated using convergent-beam electron diffraction. It has been confirmed that the space group of the room-temperature phase of Al2(WO4)3, which shows slightly negative thermal expansion, is orthorhombic Pbcn (No. 60). The space group of the low-temperature phase of Al2(WO4)3, which shows positive thermal expansion, has been determined to be monoclinic P1121/n (No. 14) with the lattice of am=ao-bo, bm=2bo, and cm=co.
    Japanese Journal of Applied Physics 06/2008; 47(6). DOI:10.1143/JJAP.47.4664 · 1.06 Impact Factor
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    ABSTRACT: Present techniques in quantitative Transmission Electron Microscopy (TEM) frequently rely on the comparison of experimental and simulated data. For example, the evaluation of the chemical composition in ternary semiconductor nanostructures (CELFA, [1]) is based on both the computation and the measurement of the contrast in (200) lattice fringe images. This technique takes advantage of the chemical sensitivity of the 200 reflections in zincblende crystals. High accuracy of the CELFA method requires a precise knowledge of structure factors (SF) to simulate the correct contrast.
  • Microscopy and Microanalysis 08/2007; 13. DOI:10.1017/S1431927607077203 · 1.76 Impact Factor

Publication Stats

768 Citations
132.41 Total Impact Points

Institutions

  • 1993–2013
    • Tohoku University
      • • Institute of Multidisciplinary Research for Advanced Materials (IMRAM)
      • • Institute for Materials Research
      Japan
  • 2006
    • Asahi Kasei
      Edo, Tōkyō, Japan
  • 2000–2001
    • Nihon University
      • College of Humanities and Sciences
      Edo, Tōkyō, Japan
    • University of Melbourne
      Melbourne, Victoria, Australia
  • 1989
    • Aoyama Gakuin University
      Edo, Tōkyō, Japan