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Sugiyama J.,Toyota Central Research and Development Laboratories Inc. | Mukai K.,Toyota Central Research and Development Laboratories Inc. | Nozaki H.,Toyota Central Research and Development Laboratories Inc. | Harada M.,Toyota Central Research and Development Laboratories Inc. | And 5 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

In order to elucidate the antiferromagnetic (AF) spin structure below TN∼35 K and to clarify the diffusive behavior of Li+ ions in the layered compound Li2MnO3, we have performed a muon-spin rotation and relaxation (μ+SR) experiment using a powder sample in the temperature range between 2 and 500 K. Below TN, the zero-field (ZF-) μ+SR spectrum showed a clear oscillation that consists of two muon-spin precession signals with different frequencies. Combining with the dipole field calculations, it was found that the most probable spin structure for Li2MnO3 is the C x-type AF order in which Mn moments align parallel or antiparallel to the a axis in the [Li1/3Mn2/3]O2 layer, and a ferromagnetic chain along the a axis aligns antiferromagnetically along both the b and c axes. The ordered Mn moment was estimated as 2.62μB at 2 K. In the paramagnetic state, ZF- and longitudinal-field μ+SR spectra exhibited a dynamic nuclear field relaxation. From the temperature dependence of the field distribution width, the Li+ ions were found to diffuse mainly along the c axis through the Li ion in the [Li 1/3Mn2/3]O2 layer. Also, based on the field fluctuation rate, a self-diffusion coefficient of Li+ ions (D Li) at 300 K was estimated as 4.7(4)×10-11 cm2/s with the thermal activation energy Ea=0.156(3) eV. © 2013 American Physical Society. Source

Jin X.,High Energy Accelerator Research Organization | Nakamoto T.,High Energy Accelerator Research Organization | Harjo S.,Japan Atomic Energy Agency | Ito T.,Comprehensive Research Organization for Science and Society | And 6 more authors.
Journal of Alloys and Compounds | Year: 2012

Nb 3Al superconducting wires produced by rapid heating and quenching (RHQ) method have been developed for application to high field accelerator magnet. In an A15-type superconductor, it is known that residual strain in the superconducting phase induced by thermal contraction after heat treatment influences superconducting properties such as the critical current density. After RHQ treatment, a solid solution of NbAl y with a bcc structure was formed from a jelly-roll of Nb and Al sheets in the wire. To observe the A15 phase transition in the NbAl y and to clarify the mechanism of residual strain generation in the RHQ-Nb 3Al wire, neutron diffraction measurements were carried out on the J-PARC "TAKUMI" between room-temperature and 800 °C, in which the Nb 3Al superconducting phase is formed. Here, we report measurements on an RHQ-Nb 3Al wire with an Nb/Ta composite matrix, using single-peak analysis and multi-peak analysis for peak intensity fitting and peak position fitting, respectively. The phase transition to the A15 was found to occur within a short period about 5 min while the temperature was increasing from 735 to 800 °C. Along the axial direction of the wire, growth of the A15 phase was found to be optimized using a subsequent holding process of 9 h at 800 °C. Following cooling to room temperature, the Nb 3Al filaments in the wire exhibited an isotropic tensile residual strain of about 0.07%. © 2012 Elsevier B.V. All rights reserved. Source

Sumita M.,Comprehensive Research Organization for Science and Society | Sumita M.,Japan National Institute of Materials Science | Morihashi K.,University of Tsukuba
Journal of Physical Chemistry A | Year: 2015

Singlet-oxygen [O2(1Δg)] generation by valence-excited thiophene (TPH) has been investigated using multireference Møller-Plesset second-order perturbation (MRMP2) theory of geometries optimized at the complete active space self-consistent field (CASSCF) theory level. Our results indicate that triplet TPH(13B2) is produced via photoinduced singlet TPH(21A1) because 21A1 TPH shows a large spin-orbit coupling constant with the first triplet excited state (13B2). The relaxed TPH in the 13B2 state can form an exciplex with O2(3σg -) because this exciplex is energetically more stable than the relaxed TPH. The formation of the TPH(13B2) exciplex with O2(3σg -) whose total spin multiplicity is triplet (T1 state) increases the likelihood of transition from the T1 state to the singlet ground or first excited singlet state. After the transition, O2(1Δg) is emitted easily although the favorable product is that from a 2 + 4 cycloaddition reaction. © 2015 American Chemical Society. Source

Machida S.,Comprehensive Research Organization for Science and Society
Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu | Year: 2016

The diamond anvil cells (DACs) for the neutron diffraction experiments were developed at the high-pressure diffraction instrument, the Spallation Neutrons and Pressure (SNAP) in the Spallation Neutron Source (SNS), Oak Ridge National Laboratory, USA. In the SNAP, the neutron data of ice VII were collected up to 94 GPa at room temperature. Also, the low temperature neutron experiments can be performed by using the DAC, PE-cell and gas-pressure-cell. In this article, the introduction for experimental techniques and review of the high-pressure neutron experiments on icy materials are shown. © 2016, Japan Society of High Pressure Science and Technology. All rights reserved. Source

Shigematsu H.,Yamaguchi University | Nishiyama K.,The University of Shimane | Kawamura Y.,Comprehensive Research Organization for Science and Society | Mashiyama H.,Yamaguchi University
Journal of the Physical Society of Japan | Year: 2014

Soft phonon modes, which are related to the normal-incommensurate phase transition at Ti = 294K and the lowesttemperature phase transition at T3 = 66K in Rb2CoCl4, have been measured by inelastic neutron scattering. For the normal-incommensurate phase transition, phonon dispersion curves have been determined in the low-temperature commensurate phases, and the phase mode has been observed far below Ti. The soft mode is fully overdamped above Ti. Moreover, another soft phonon mode, which contributes to the phase transition at T3, has been observed. Furthermore, the space group of the lowest phase is directly confirmed to be C1c1 by verifying extinction rules of X-ray diffraction. It has been recognized that the ratio of the ionic radius of A+ to the average bond length B-X in the tetrahedral BX4 2- ion can control the phase transition sequence. Rb2CoCl4 belongs to the group in which this ratio is in the range from 0.69 to 0.85, and the transition temperature decreases loosely with increasing the lattice parameter ratio c0/a0, where a0 and c0 are the lattice parameters of the normal phase. © 2014 The Physical Society of Japan. Source

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