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ABSTRACT: We assess the imaging performance of a transmission electron microscopy (TEM) system operated at a relatively low acceleration voltage using the three-dimensional (3D) Fourier transform of through-focus images. Although a single diffractogram and the Thon diagram cannot distinguish between the linear and non-linear TEM imaging terms, the 3D Fourier transform allows us to evaluate linear imaging terms, resulting in a conclusive assessment of TEM performance. Using this method, information transfer up to 98pm is demonstrated for an 80kV TEM system equipped with a spherical aberration corrector and a monochromator. We also revisit the Young fringe method in the light of the 3D Fourier transform, and have found a considerable amount of non-linear terms in Young fringes at 80kV even from a typical standard specimen, such as an amorphous Ge thin film.
Ultramicroscopy 06/2012; 121:31-7. · 2.47 Impact Factor
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ABSTRACT: We investigated the texture of charge modulations and behaviors of their domains in the ferromagnetic insulating state of La1-x SrxMnO3 (x = 0.125) by low-temperature transmission electron microscopy. We observed simultaneous evolutions of three charge-modulated phases below similar to 135 K, close to the charge-ordering-transition temperature T-CO similar to 140 K. The phases form intricate domain structures within one ferromagnetic phase. This indicates that one magnetic state exhibits multiple-charge states. With further decreasing temperature, below similar to 40 K, the three charge-modulated phases behave differently from one another. We consider that the behaviors would lead to a phase separation into the ferromagnetic insulating phase and the ferromagnetic metallic one.
Physical review. B, Condensed matter 05/2011; 83(17):174401.
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ABSTRACT: An aligned polyacetylene (PA) film was synthesized in a macroscopically-aligned nematic liquid crystal (N-LC) solvent using a gravity-flow method. Long and single nanofibers of less than 100 nm in radius were successfully prepared by ultrasonication of the aligned PA film immersed in ethanol. The usual PA film was synthesized in an isotropic solvent, such as toluene, only yielding short and non-dispersed fibers after the ultrasonication due to the entangled fibril morphology. Entanglement-free fibrils of the aligned PA were well-separated into single fibrils through ultrasonication, even without a surfactant.
Nanoscale 04/2010; 2(4):509-14. · 5.91 Impact Factor
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ABSTRACT: Self-organizing domain structures of charge-orbital-ordered (COO) and ferro-orbital-ordered (FOO) phases were observed for tetragonal layered manganites Nd1-xSr1+xMnO4 (x = 0.8 and 0.82) by low-temperature transmission electron microscopy. We revealed a marked temperature variation of coexisting COO domains with equivalent structural distortions and orbital ordering patterns at x=0.8. The observed competition of coexisting FOO domains at x=0.82 also clearly reflects the self-organizing nature of e(g) electrons. Furthermore, a checkered structure, in which COO domains were reproduced at the intersections of FOO domains, was found in the transition from the COO phase to the FOO phase at x=0.8. The observations suggest that strain energy affects the self-organizing behavior in the orbital ordering.
Physical review. B, Condensed matter 02/2010; 81(6):060407.
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ABSTRACT: We report a local crystal structure analysis with a high precision of several picometers on the basis of scanning transmission electron microscopy (STEM). Advanced annular dark-field (ADF) imaging has been demonstrated using software-based experimental and data-processing techniques, such as the improvement of signal-to-noise ratio, the reduction of image distortion, the quantification of experimental parameters (e.g., thickness and defocus) and the resolution enhancement by maximum-entropy deconvolution. The accuracy in the atom position measurement depends on the validity of the incoherent imaging approximation, in which an ADF image is described as the convolution between the incident probe profile and scattering objects. Although the qualitative interpretation of ADF image contrast is possible for a wide range of specimen thicknesses, the direct observation of a crystal structure with deep-sub-angstrom accuracy requires a thin specimen (e.g., 10nm), as well as observation of the structure image by conventional high-resolution transmission electron microscopy.
Ultramicroscopy 11/2009; 110(7):778-82. · 2.47 Impact Factor
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Masahiro Sadakane,
Keiko Yamagata,
Katsunori Kodato,
Keisuke Endo,
Koshiro Toriumi,
Yoshiki Ozawa,
Tomoji Ozeki, Takuro Nagai,
Yoshio Matsui,
Norihito Sakaguchi,
William D Pyrz,
Douglas J Buttrey,
Douglas A Blom,
Thomas Vogt,
Wataru Ueda
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ABSTRACT: Mix and match: The pentagonal [Mo(6)O(21)](n-) polyoxomolybdate building block assembles with other sources of Mo, V, and Sb ions to form an orthorhombic Mo-V-Sb oxide. The first single-crystal X-ray analysis of an orthorhombic Mo-V-based oxide, a promising catalyst for light alkane selective oxidation known as the "M1 phase", revealed the structure of the compound.
Angewandte Chemie International Edition 04/2009; 48(21):3782-6. · 13.45 Impact Factor
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ABSTRACT: We demonstrate local crystal structure analysis based on annular dark-field (ADF) imaging in scanning transmission electron microscopy (STEM). Using a stabilized STEM instrument and customized software, we first realize high accuracy of elemental discrimination and atom-position determination with a 10-pm-order accuracy, which can reveal major cation displacements associated with a variety of material properties, e.g. ferroelectricity and colossal magnetoresistivity. A-site ordered/disordered perovskite manganites Tb(0.5)Ba(0.5)MnO(3) are analysed; A-site ordering and a Mn-site displacement of 12 pm are detected in each specific atomic column. This method can be applied to practical and advanced materials, e.g. strongly correlated electron materials.
Journal of electron microscopy 12/2008; 58(3):131-6. · 1.31 Impact Factor
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ABSTRACT: In this communication, we report a novel preparation of the helical carbon nanofibril-fabricated thin film from the iodine-doped filmy helical polyacetylene through a carbonization process. Carbonization of the helical polyacetylene films by way of iodine doping is found to afford carbon and graphitic films completely preserving morphologies and even helical nanofibril structures.
Journal of the American Chemical Society 08/2008; 130(33):10880-1. · 9.91 Impact Factor
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ABSTRACT: A tubular-shaped polyaniline less than 5 microm in length and 170 nm in outer diameter was synthesized by a self-assembly process using D-camphorsulfonic acid as a dopant. A tubular-shaped nanocarbon was prepared from the tubular-shaped polyaniline by means of pyrolysis at 1000 degrees C in argon gas. The structural and electrical properties of the resultant tubular-shaped nanocarbons were investigated using Raman scattering spectrum, X-ray diffraction measurements, scanning and transmission electron microscopes, and a low resistivity meter. The tubular-shaped nanocarbons are very short in length and are an amorphous state. The short length and amorphous tubular-shaped nanocarbon were crystallized to some extent by heat-treatment at 2600 degrees C. The tubular-shaped nanocarbons mentioned in this work are appropriate for mass production, compared to the well-known multi-walled carbon nanotubes. The electrical conductively of the tubular-shaped polyaniline was remarkably improved by the carbonization and was enhanced by the heat-treatment.
Journal of Nanoscience and Nanotechnology 05/2008; 8(4):1999-2004. · 1.56 Impact Factor
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Angewandte Chemie International Edition 02/2008; 47(13):2493-6. · 13.45 Impact Factor
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ABSTRACT: Microstructure characterization has become indispensable to the study of complex materials, such as strongly correlated oxides, and can obtain useful information about the origin of their physical properties. Although atomically resolved measurements have long been possible, an important goal in microstructure characterization is to achieve element-selective imaging at atomic resolution. A combination of scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) is a promising technique for atomic-column analysis. However, two-dimensional analysis has not yet been performed owing to several difficulties, such as delocalization in inelastic scattering or instrumentation instabilities. Here we demonstrate atomic-column imaging of a crystal specimen using localized inelastic scattering and a stabilized scanning transmission electron microscope. The atomic columns of La, Mn and O in the layered manganite La1.2Sr1.8Mn2O7 are visualized as two-dimensional images.
Nature 12/2007; 450(7170):702-4. · 36.28 Impact Factor
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Masahiro Nagao,
Toru Asaka, Takuro Nagai,
Daisuke Akahoshi,
Ryota Hatakeyama,
Tadahiro Yokosawa,
Masahiko Tanaka,
Hideki Yoshikawa,
Atsushi Yamazaki,
Koji Kimoto,
Hideki Kuwahara,
Yoshio Matsui
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ABSTRACT: We investigated the crystal structures of single-crystal Nd0.2Sr0.8MnO3 by means of synchrotron x-ray diffraction measurement and transmission electron microscopy. We observed the coexistence of distinct crystal-structural phases, i.e., tetragonal (orbital ordered) and cubic (orbital disordered) phases, over a significantly wide range of temperatures. The ratio of these phases varied continuously with temperature. These indicate that the crystal exhibits a diffuse phase transition of the 3z(2) - r(2)-type orbital ordering. Moreover, we observed the anisotropic evolution of the orbital-ordered nanodomains in the cubic phase. This specific nature of the phase transition probably originates from the competition between the orbital order and disorder.
Journal of the Physical Society of Japan 10/2007; 76(10):103706. · 2.36 Impact Factor
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ABSTRACT: We synthesized a new cobalt oxide (CaOH)(1.14)CoO2 by utilizing a high-pressure technique. X-ray and electron diffraction studies revealed that the compound has a layered structure that consists of Cdl(2)-type CoO2 layers and rock-salt-type double CaOH atomic layers. The two subcells have incommensurate periodicity along the a-axis, resulting in a misfit-layered structure. From resistivity and Seebeck coefficient measurements, we have shown that the two-dimensional (2-D) variable-range hopping (VRH) regime with hole conduction is dominant at low temperature for this compound. As temperature increases, the conduction mechanism undergoes crossover from the 2-D VRH regime to a thermal activation-energy-type regime.
Journal of Solid State Chemistry 01/2007; 180:249. · 2.16 Impact Factor
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ABSTRACT: A monoclinic phase of the misfit-layered cobalt oxide (Ca{sub 0.85}OH){sub 1.16}CoO{sub 2} was successfully synthesized and characterized. It was found that this new material is a poly-type phase of the orthorhombic form of (CaOH){sub 1.14}CoO{sub 2}, recently discovered by the present authors. Both the compounds consist of two interpenetrating subsystems: CdI{sub 2}-type CoO{sub 2} layers and rock-salt-type double-atomic-layer CaOH blocks. However, these two phases exhibit a different stacking structure. By powder X-ray and electron diffraction (ED) studies, it was found that the two subsystems of (Ca{sub 0.85}OH){sub 1.16}CoO{sub 2} have c-centered monoclinic Bravais lattices with common a=4.898 A, c=8.810 A and {beta}=95.8{sup o} lattice parameters, and different b parameters: b {sub 1}=2.820 A and b {sub 2}=4.870 A. Chemical analyses revealed that the monoclinic phase has a cobalt valence of +3.1-3.2. Resistivity of the monoclinic phase is approximately 10{sup 1}-10{sup 5} times lower than that of the orthorhombic phase. This suggests that the monoclinic phase is a hole-doped phase of the insulating orthorhombic phase. Furthermore, large positive Seebeck coefficients ({approx}100 {mu}V/K) were observed near room temperature. - Graphical abstract: Crystal structure of two kinds of poly-type phases of the misfit-layered cobalt oxides (Ca{sub 1-} {sub {delta}} OH) {sub x} CoO{sub 2}: (a) projection along the a-axis of the orthorhombic structure; (b) projection along the b-axis of the monoclinic structure; and (c) projection along the [-1 0 0] direction of the clinic structure. In each case, the rectangle is the unit cell.
Journal of Solid State Chemistry. 12/2006; 179(12).
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ABSTRACT: We have performed magnetic susceptibility and electron diffraction measurements on impurity effect in a novel spin-Peierls system TiOBr, i.e. Ti1-xScxOBr.The impurity-induced antiferromagnetic long-range order found in Cu1-xZnxGeO3 could not be observed in this system. A number of unpaired spins induced by the impurities can be explained by a simple model that one Sc impurity creates one S = (1)/(2) spin up to the threshold concentration, x(c)similar to 0.025. The induced impurity suppresses the spin-Peierls transition temperature, T-c1 and the spin-Peierls phase disappears at x(1)similar to 0.028, although the incommensurate state still persists above x(1). Both values agree well with each other.
Physica B Condensed Matter 08/2006; 383:1-4. · 1.06 Impact Factor
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ABSTRACT: A new form of LiMn2O4 is reported. The structure is the CaFe2O4-type and 6% denser than the spinel. The structure transformation was achieved by heating at 6 GPa. Analysis of the neutron diffraction pattern confirmed an average of the structure; the unit cell was orthorhombic at a = 8.8336(5) angstroms, b = 2.83387(18) angstroms, and c = 10.6535(7) angstroms (Pnma). Electron diffraction patterns indicated an order of superstructure 3a x b x c, which might be initiated by Li vacancies. The exact composition is estimated at Li(0.92)Mn2O4 from the structure analysis and quantity of intercalated Li. The polycrystalline CaFe2O4-type compound showed semiconducting-like characters over the studied range above 5 K. The activation energy was reduced to approximately 0.27 eV from approximately 0.40 eV at the spinel form, suggesting a possible enhancement of hopping mobility. Magnetic and specific-heat data indicated a magnetically glassy transition at approximately 10 K. As the CaFe2O4-type transition was observed for the mineral MgAl2O4, hence the new form of the lithium manganese oxide would provide valuable opportunities to study not only the magnetism of strongly correlated electrons but also the thermodynamics of the phase transition in the mantle.
Journal of the American Chemical Society 08/2006; 128(29):9448-56. · 9.91 Impact Factor
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Alexei A Belik,
Satoshi Iikubo,
Katsuaki Kodama,
Naoki Igawa,
Shin-ichi Shamoto,
Makoto Maie, Takuro Nagai,
Yoshio Matsui,
Sergey Yu Stefanovich,
Bogdan I Lazoryak,
Eiji Takayama-Muromachi
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ABSTRACT: With neutron powder diffraction, electron diffraction, and second-harmonic generation, we have shown that BiScO3 has a structure closely related to that of multiferroic BiMnO3, but BiScO3 crystallizes in the centrosymmetric space group of C2/c. These results bring up a question about the origin of ferroelectricity in BiMnO3. BiScO3 may serve as a model system to understand the role of Mn3+ ions in the ferroelectricity of BiMnO3.
Journal of the American Chemical Society 02/2006; 128(3):706-7. · 9.91 Impact Factor
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ABSTRACT: A monoclinic phase of the misfit-layered cobalt oxide (Ca0.85OH)(1.16)CoO2 was successfully synthesized and characterized. It was found that this new material is a poly-type phase of the orthorhombic form of (CaOH)(1.14)CoO2, recently discovered by the present authors. Both the compounds consist of two interpenetrating subsystems: CdI2-type CoO2 layers and rock-salt-type double-atomic-layer CaOH blocks. However, these two phases exhibit a different stacking structure. By powder X-ray and electron diffraction (ED) studies, it was found that the two subsystems of (Ca0.85OH)(1.16)CoO2 have c-centered monoclinic Bravais lattices with common a= 4.898 angstrom, c = 8.810 angstrom and beta = 95.8 degrees lattice parameters, and different b parameters: b(1) = 2.820 angstrom and b(2) = 4.870 angstrom. Chemical analyses revealed that the monochnic phase has a cobalt valence of + 3.1-3.2. Resistivity of the monoclinic phase is approximately 10(1)-10(5) times lower than that of the orthorhombic phase. This suggests that the monoclinic phase is a hole-doped phase of the insulating orthorhombic phase. Furthermore, large positive Seebeck coefficients (similar to 1000 mu V/K) were observed near room temperature.
Journal of Solid State Chemistry 01/2006; 179:3974. · 2.16 Impact Factor
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ABSTRACT: The crystal structure of our newly discovered Sr-Co-O phase is investigated in detail through high-resolution electron microscopy (HREM) techniques. Electron diffraction (ED) measurement together with energy dispersive X-ray spectroscopy (EDS) analysis show that an ampoule-synthesized sample contains an unknown Sr-Co-O ternary phase with monoclinic symmetry and the cation ratio of Sr/Co = 1. From HREM images a layered structure with a regular stacking of a CdI2-type CoO, sheet and a rock-salt-type Sr2O2 double-layered block is observed, which confirms that the phase is the parent of the more complex "misfit-layered (ML)" cobalt oxides of [M(m)A(2)O(m+2)],CoO2 with the formula of [Sr2O2](q)CoO2, i.e. m = 0. It is revealed that the misfit parameter q is 0.5, i.e. the two sublattices of the CoO2 sheet and the Sr2O2 block coexist to form a commensurate composite structure. We propose a structural model with monoclinic P2(1)/m symmetry, which is supported by simulations of ED patterns and HREM images based on dynamical diffraction theory.
Journal of Solid State Chemistry 01/2006; 179:1898. · 2.16 Impact Factor
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ABSTRACT: New oxides, BiAlO3 and BiGaO3, were prepared using a high-pressure high-temperature technique at 6 GPa and 1273−1473 K. BiAlO3 is isotypic with multiferroic perovskite-like BiFeO3 and has octahedrally coordinated Al3+ ions. Structure parameters of BiAlO3 were refined from laboratory X-ray powder diffraction data (space group R3c; Z = 6; a = 5.37546(5) Å and c = 13.3933(1) Å). BiGaO3 has the structure closely related to pyroxene-like KVO3. Structure parameters of BiGaO3 were refined from time-of-flight neutron powder diffraction data (space group Pcca; Z = 4; a = 5.4162(2) Å, b = 5.1335(3) Å, and c = 9.9369(5) Å). The GaO4 tetrahedra in BiGaO3 are joined by corners forming infinite (GaO3)3- chains along the a axis. Bi3+ ions in BiGaO3 have 6-fold coordination. Both BiAlO3 and BiGaO3 decompose at ambient pressure on heating above 820 K to give Bi2M4O9 and Bi25MO39 (M = Al and Ga). Vibrational properties of BiAlO3 and BiGaO3 were studied by Raman spectroscopy. In solid solutions of BiAl1-xGaxO3, a C-centered monoclinic phase structurally related to PbTiO3 with lattice parameters of a = 5.1917(4) Å, b = 5.1783(4) Å, c = 4.4937(3) Å, and β = 91.853(3)° was found.
12/2005;
