Yoshihiro Kudo

Reaction Mechanism of the Olivine-Type Li x ( Mn0.6Fe0.4 ) PO 4 ( 0 ⩽ x ⩽ 1 )

The charge-discharge reaction mechanism of the olivine-type Li x (Mn 0.6 Fe 0.4 )PO 4 (0 ≤ x ≤ 1.0), a possible 4 V class cathode material for lithium batteries, was investigated using equilibrium voltage measurements, X-ray diffraction. Mossbauer spectroscopy, and X-ray absorption spectroscopy. The flat two-phase region with an open-circuit voltage (OCV) of ca. 4.1 V (region 1: 0 ≤ x ≤ 0.6, Mn 3+ /Mn 2+ ) and the S-curved single-phase region with OCV 3.5 V (region 11: 0.6 ≤ x ≤ 1.0, Fe 3+ /Fe 2+ ) were clearly identified together with the corresponding change in the unit cell dimensions of the orthorhombic lattice. These features show significant differences from the reaction mechanism of Li x FePO 4 (0 ≤ x ≤ 1) ), in which the whole Fe 3+ /Fe 2+ reaction proceeds in a two-phase manner (LiFePO 4 -FePO 4 ) with a flat voltage profile at 3.4 V.

Hopping and band mobilities of pentacene, rubrene, and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) from first principle calculations

Hopping and band mobilities of holes in organic semiconductors at room temperature were estimated from first principle calculations. Relaxation times of charge carriers were evaluated using the acoustic deformation potential model. It is found that van der Waals interactions play an important role in determining accurate relaxation times. The hopping mobilities of pentacene, rubrene, and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) in bulk single crystalline structures were found to be smaller than 4 cm(2)∕Vs, whereas the band mobilities were estimated between 36 and 58 cm(2)∕Vs, which are close to the maximum reported experimental values. This strongly suggests that band conductivity is dominant in these materials even at room temperature.

Characterization of process-induced lattice distortion in silicon by double-crystal x-ray topography using a curved collimator

Instead of the conventional flat collimator a curved collimator was used in double-crystal x-ray topography. The curvature of the collimator was adjusted so that the Bragg condition for x-ray diffraction was uniformly satisfied over a wide area of the silicon wafer. The image area of the wafer was wide enough to characterize the local lattice distortion induced by test element groups of metal–oxide–semiconductor capacitors formed on the wafer. The lattice distortion was measured as variations in lattice plane spacing and in lattice plane orientation using local angular deviations from the Bragg condition. These angular deviations were determined by fitting the x-ray intensities measured at the same point on a series of topographs taken around the Bragg peak to the rocking curve of the sample. The lattice plane spacing changed abruptly by 10−6 at the boundary between the areas of gate oxide (11 nm thick) and the areas of field oxide (400 nm thick), and showed less variation within these areas. The lattice ...

Complex Structures and Electrochemical Properties of Magnesium Electrolytes

Magnesium organohaloaluminate in tetrahydrofuran [0.25 mol/L Mg(AlCl 2 EtBu) 2 /THF, Et:C 2 H 5 ,Bu:C 4 H 9 ] is an electrolyte solution that is able to deposit and dissolve magnesium electrochemically and reversibly at room temperature. It has been reported that the electrochemical window is ruled by Lewis acidity of the aluminum compounds involved, and some complex species formed in the electrolyte have been suggested based on the analysis of nuclear magnetic resonances and Raman spectroscopy. Because in these analytical methods there are not enough controls to identify all the included compounds, neither the complete complex structures nor the mechanism of the reversible reaction has been revealed yet. Here, we show the complete complex structures in this electrolyte directly observed by the X-ray absorption fine structure measurements, which reveal the reversible equilibrium reaction as well as the other electrochemical properties of this electrolyte.

Structure Analysis of InN Film Using Extended X-Ray Absorption Fine Structure Method

We investigated the local atomic structure around In atoms of MBE-grown InN which has a direct bandgap energy of 0.8 eV, using extended X-ray absorption fine structure (EXAFS) oscillation of In K-edge. The signals from the first-nearest neighbor atoms (N) and second-nearest atoms (In) from In atoms were clearly observed and the atomic bond length of In-N and In-In was estimated to be d In-In = 0.215 nm and d In-In = 0.353 nm, respectively. The In-N bond length of d In-In = 0.353 nm was closed to the a-axis lattice constant of a = 0.3536 nm, which was determined using X-ray diffraction measurements. The obtained local atomic structure agreed with the calculated ideal structure. We conclude, therefore, that the InN film with a bandgap energy of 0.8 eV has a high structural symmetry in the range of a few A around In atoms.

Structural changes of manganese spinel at elevated temperatures

Abstract A chemical synthesis route to Cr-doped and undoped Mn spinel was developed for the purpose of detailed structural analysis for elucidating the relationship between storage performance and structural changes at elevated temperatures. We identified a two-phase segregation in the lithium compositional range of 0.6

High-resolution measurements of nuclear Bragg scattering from a synthetic α-57Fe2O3 crystal

Nuclear Bragg scattering from a synthesized α-57Fe2O3 crystal was observed with 450 cps at beamline 16 of the Photon Factory. Mossbauer absorption spectra of the scattered beam were measured by oscillating the scatterer crystal while maintaining its Bragg condition. Time distribution of the scattered beam was measured with 300 ps resolution.

Plane‐Wave X‐Ray Topography Using Imaging Plates and Its Application to Characterization of Lattice Distortion in As‐Grown Silicon

Imaging plates were applied to plane-wave x-ray diffraction topography using synchrotron radiation to perform quantitative analysis of minute lattice distortion in as-grown silicon crystals. The lattice distortion was separated into variations in lattice-plane spacing, Δd/d, and variations in lattice-plane orientation, Δα 1 by analysis of intensity variations in the digitized topographs. The variations in Δd/d along the growth direction in magnetic Czochralski (MCZ) silicon were closely correlated with fluctuations in the oxygen concentration. The concentric striation pattern observed in Czochralski silicon crystals was interpreted in terms of the variations in Δd/d, while the variations in Δα revealed the existence of frozen-in strains. In a ring-shaped area of oxidation-induced stacking faults in another Czochralski silicon crystal, a valley in the variations in Δd/d was observed, but no valley in the variations in Δα. In floating-zone silicon, Δd/d increased from an area in which D defects were distributed to an area in which A defects were distributed, and Δα began to decrease at the boundary between the neutral area, in which neither D defects nor A defects were distributed, and the A-defect area.

Performance of an imaging plate as an x‐ray area detector used for plane‐wave x‐ray diffraction topography

We report the linearity, spatial resolution, and granularity of x‐ray intensity images recorded on imaging plates (IPs). The IP‐processing system, designed for use with a transmission electron microscope (TEM), was used to evaluate the influence of these characteristics on profiles of local lattice distortion in silicon obtained by plane‐wave x‐ray diffraction topography (PWT). The signal intensity was linear with x‐ray doses over four orders of magnitude of intensity, as has also been reported in the case of TEM. The modulation transfer function and root mean square of x‐ray intensity images were measured to evaluate the spatial resolution and granularity. The results indicate that profiles of lattice distortion with a period of more than 0.5 mm can be reproduced by PWT in combination with the present IP‐processing system.

Novel Analysis System of Imaging-Plate Plane-Wave X-Ray Topography for Characterizing Lattice Distortion in Silicon

This letter reports that a novel analysis system has been developed to determine lattice distortion in silicon single crystals from plane-wave X-ray topographs taken using synchrotron radiation. The system analyzes the topographs recorded on the imaging plate and gives the distortion as local variations in spacing and orientation of the lattice plane. Line analysis and mapping of the distortion in any position on the topograph can be easily performed in the system due to the overall digitization by the imaging plate.