Shuki Torii

High Energy Accelerator Research Organization, Tsukuba, Ibaraki, Japan

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Publications (30)55.33 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: K2NiF4-type LaSrAlO4 and Sr2TiO4 exhibit anisotropic and isotropic thermal expansion, respectively; however, their structural origin is unknown. To address this unresolved issue, the crystal structure and thermal expansion of LaSrAlO4 and Sr2TiO4 have been investigated through high-temperature neutron and synchrotron X-ray powder diffraction experiments and ab initio electronic calculations. The thermal expansion coefficient (TEC) along the c-axis (αc) being higher than that along the a-axis (αa) of LaSrAlO4 [αc = 1.882(4)αa] is mainly ascribed to the TEC of the interatomic distance between Al and apical oxygen O2 α(Al-O2) being higher than that between Al and equatorial oxygen O1 α(Al-O1) [α(Al-O2) = 2.41(18)α(Al-O1)]. The higher α(Al-O2) is attributed to the Al-O2 bond being longer and weaker than the Al-O1 bond. Thus, the minimum electron density and bond valence of the Al-O2 bond are lower than those of the Al-O1 bond. For Sr2TiO4, the Ti-O2 interatomic distance, d(Ti-O2), is equal to that of Ti-O1, d(Ti-O1) [d(Ti-O2) = 1.0194(15)d(Ti-O1)], relative to LaSrAlO4 [d(Al-O2) = 1.0932(9)d(Al-O1)]. Therefore, the bond valence and minimum electron density of the Ti-O2 bond are nearly equal to those of the Ti-O1 bond, leading to isotropic thermal expansion of Sr2TiO4 than LaSrAlO4. These results indicate that the anisotropic thermal expansion of K2NiF4-type oxides, A2BO4, is strongly influenced by the anisotropy of B-O chemical bonds. The present study suggests that due to the higher ratio of interatomic distance d(B-O2)/d(B-O1) of A2(2.5+)B(3+)O4 compared with A2(2+)B(4+)O4, A2(2.5+)B(3+)O4 compounds have higher α(B-O2), and A2(2+)B(4+)O4 materials exhibit smaller α(B-O2), leading to the anisotropic thermal expansion of A2(2.5+)B(3+)O4 and isotropic thermal expansion of A2(2+)B(4+)O4. The "true" thermal expansion without the chemical expansion of A2BO4 is higher than that of ABO3 with a similar composition.
    Inorganic Chemistry 04/2015; 54(8). DOI:10.1021/acs.inorgchem.5b00102 · 4.79 Impact Factor
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    ABSTRACT: The development of lithium ion battery technology is very important in its utilization as a new energy sources, for example in electrical vehicle (EV). One of the components that affect the performance of the battery is the cathode, such as spinel LiMn2O4. In an effort to obtain a good cathode material it is necessary to set the proper synthesis conditions. In this study, spinel LiMn2O4 powder was synthesized from LiOH.H2O and MnOx by mechanical alloying (MA) method followed by heat treatment at 700°C, 800oC and 900oC. The influence of morphology and crystal structure of the spinel LiMn2O4 as a result of heat treatment on electrochemical performance was investigated. Observation by SEM showed that the higher the annealing temperature, the crystallinity of the powder particles of the spinel LiMn2O4 increased. Phase and crystal structure analysis by XRD showed that the purity and crystallinity of the spinel LiMn2O4 increased with annealing temperature, characterized by sharper peaks of the diffraction patterns. Crystal structure analysis by neutron powder diffraction (NPD) showed that LiMn2O4 synthesized has spinel structure with space group Fd-3m and lattice parameter of 8.233316(8) Å, 8.239790(5) Å and 8.244564(4) Å for annealing temperatures of 700oC, 800oC and 900oC. It is also found that the electrochemical performance of LiMn2O4 cathode in Liion battery increased with annealing temperature, shown by capacity of 248.95 mAhg-1, 264.29 mAhg-1and 277.24 mAhg-1. These results show that increasing purity and crystallinity of the cathode material LiMn2O4 are significantly affect the electrochemical performance of Li-ion battery.
    14th Asian Conference on Solid State Ionics (ACSSI 2014), NUS SIngapore; 06/2014
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    ABSTRACT: The structural, magnetic and electrical properties of the mixed Ti-Mn oxides Sr1-xLaxTi0.5Mn0.5O3 (0 ≤ x ≤ 0.5) are reported. At room temperature the oxides have a cubic structure in space group Pm3[combining macron]m for x ≤ 0.25 and rhombohedral in R3[combining macron]c for 0.3 ≤ x ≤ 0.50. X-ray absorption spectroscopic measurements demonstrate the addition of La(3+) is compensated by the partial reduction of Mn(4+) to Mn(3+). Variable temperature neutron diffraction measurements show that cooling Sr0.6La0.4Ti0.5Mn0.5O3 results in a first order transition from rhombohedra to an orthorhombic structure in Imma. Complex magnetic behaviour is observed. The magnetic behaviour of the mixed valent (Mn(3+/4+)) examples is dominated by ferromagnetic interactions, although cation disorder frustrates long range magnetic ordering.
    Dalton Transactions 03/2014; 43(18). DOI:10.1039/c3dt53406e · 4.20 Impact Factor
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    ABSTRACT: High-temperature (high-$T_{\rm c}$) superconductivity appears as a consequence of the carrier-doping of an undoped parent compound exhibiting antiferromagnetic order; thereby, ground-state properties of the parent compound are closely relevant to the superconducting state. On the basis of the concept, a spin-fluctuation has been addressed as an origin of pairing of the superconducting electrons in cuprates. Whereas, there is growing interest in the pairing mechanism such as an unconventional spin-fluctuation or an advanced orbital-fluctuation due to the characteristic multi-orbital system in iron-pnictides. Here, we report the discovery of an antiferromagnetic order as well as a unique structural transition in electron-overdoped LaFeAsO$_{1-x}$H$_x$ ($x$ ~ 0.5), whereby another parent phase was uncovered, albeit heavily doped. The unprecedented two-dome superconducting phases observed in this material can be interpreted as a consequence of the carrier-doping starting from the original at $x\sim0$ and advanced at $x\sim0.5$ parent phases toward the intermediate region. The bipartite parent phases with distinct physical properties in the second magnetic phase provide us with an interesting example to illustrate the intimate interplay among the magnetic interaction, structural change and orbital degree of freedom in iron-pnictides.
    Nature Physics 03/2014; 10(4). DOI:10.1038/NPHYS2906 · 20.60 Impact Factor
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    ABSTRACT: In order to investigate an effect of the preparation process on protonic conductivity of La1−xBa1+xGaO4−δ, we attempt to prepare the samples with x = 0.1, La0.9Ba1.1GaO4−δ, by a liquid synthesis method as well as a conventional solid-phase method. Their electrical conductivities are measured from 300 to 900°C in various water vapor partial pressures, PH2O. From the result, it is found that the protonic conductivity is higher in the sample synthesized by the liquid synthesis method compared with that by the solid-phase method. In addition, it is also indicated that the PH2O-dependence of the electrical conductivity around 600°C is more significant in the sample prepared by the liquid synthesis method. This result implies that this method enhances proton dissolution in La0.9Ba1.1GaO4−δ at least around the temperature range. To investigate a crystal structure change by the synthesis method, we perform powder neutron diffraction measurements. The Rietveld and maximum entropy method (MEM) analyses demonstrate that nuclear density of the proton is clearly observed between neighboring O3 sites, and suggest that the liquid synthesis method makes a site occupancy of proton higher.
    Electrochemistry -Tokyo- 01/2014; 82(7):550-556. DOI:10.5796/electrochemistry.82.550 · 0.98 Impact Factor
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    ABSTRACT: We have investigated the crystal structure of (Bi1/2Na1/2)TiO3-7%BaTiO3 (BNT-7%BT) by high-resolution neutron powder diffraction (NPD) and high-energy synchrotron radiation X-ray diffraction (SR-XRD) analyses. The NPD study revealed that the BNT-7%BT crystals have a single-phase tetragonal structure with P4bm symmetry. The crystal structure refined by the Rietveld method was found to be similar to the ferrielectric P4bm phase reported for BNT at a high temperature of 673 K. The SR-XRD analyses for single crystals of BNT-7%BT demonstrated that the P4bm phase remains as a stable phase in the crystals even after a high electric field is applied for poling, which is different from the structural analysis of ceramics by Ma et al. [Phys. Rev. Lett. 109 (2012) 107602]. (C) 2013 The Japan Society of Applied Physics
    Japanese Journal of Applied Physics 09/2013; 52(9S1):09KD01. DOI:10.7567/JJAP.52.09KD01 · 1.06 Impact Factor
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    ABSTRACT: Oxide ion conduction and phase transition phenomena have been investigated on La2 − xPbxMo2O9 − x/2 solid solutions (x ≤ 0.6). X-ray and neutron diffraction experiments as well as thermal analyses indicate that a single phase of high-temperature polymorph (β-phase) is preserved down to room temperature for the composition of x ≥ 0.06. In the solid solution range, ionic conductivity gradually decreases with Pb-substitution. Such phase transition and ionic conduction properties of La2 − xPbxMo2O9 − x/2 are quite similar to the Bi-substituted system, La2 − xBixMo2O9, although ionic conductivity at lower temperatures is slightly higher in the former system than the latter with the same-amount of substitution. Room temperature neutron diffraction experiment suggests that oxide-ion deficiency is introduced mainly into O2 site by the charge compensation with Pb-substitution, which would contribute to a little enhancement in conductivity compared with Bi-substituted samples along with the variation of nearest O2O3 bond length.
    Solid State Ionics 05/2013; 238:36–43. DOI:10.1016/j.ssi.2013.03.001 · 2.11 Impact Factor
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    ABSTRACT: Solid solutions of (1-x)BiFeO3--xBaTiO3 (x = 0.0{--}1.0) were studied by the combination of X-ray and neutron powder diffraction methods in order to investigate structural and magnetic properties over a wide temperature region. The structure analyses revealed that there exists a hexagonal phase over the wide range of x, and a coexistence of a cubic or a tetragonal phase was revealed. The compositions of the two coexisting phases differ from each other, and Ba and Ti were found to favor the cubic or tetragonal phase. As x increases, the relaxation of the rhombohedral distortion in the hexagonal phase was observed. The decreases of the ferroelectric and the antiferromagnetic phase transition temperatures were also observed leading the suppression of the polarization and the magnetic moment of Fe3+ ion at room temperature. As a whole, the ferroelectricity and ferromagnetism in this material were considered to arise from the remaining hexagonal phase.
    Journal of the Physical Society of Japan 02/2012; 81(2):4603-. DOI:10.1143/JPSJ.81.024603 · 1.48 Impact Factor
  • Journal of the Physical Society of Japan 01/2011; 80(Suppl.B):SB001. DOI:10.1143/JPSJS.80SB.SB001 · 1.48 Impact Factor
  • Journal of the Physical Society of Japan 01/2011; 80(Suppl.B):SB020. DOI:10.1143/JPSJS.80SB.SB020 · 1.48 Impact Factor
  • 01/2011; 36(2):285-288. DOI:10.14723/tmrsj.36.285
  • ChemInform 11/2010; 33(46). DOI:10.1002/chin.200246005
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    ABSTRACT: The crystal structures and dielectric, polarization, and piezoelectric properties of high-density x(Bi0.5K0.5)TiO3–(1−x)BiFeO3 ceramics were investigated. The results obtained using x-ray and neutron powder diffractions and transmission electron microscopy showed that a morphotropic phase boundary between the rhombohedral (ferroelectric) and pseudocubic (ferroelectric) phases is present in 0.4<x<0.43. Ceramics with x = 0.4 exhibited a large remanent polarization of 52 μC/cm2 at 25 °C and their piezoelectric properties were maintained up to 300 °C. It is suggested that the presence of nanosized domains with a polar rhombohedral structure observed for x = 0.4 is the origin of relaxor-like dielectric properties.
    Journal of Applied Physics 11/2010; 108(10):104103-104103-6. DOI:10.1063/1.3506717 · 2.19 Impact Factor
  • Takashi Kamiyama · Shuki Torii
    01/2009; 48(7):353-354. DOI:10.2320/materia.48.353
  • 01/2008; 50(1):18-23. DOI:10.5940/jcrsj.50.18
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    ABSTRACT: We have developed a prototype data acquisition and device control system for experiment instruments at the Material and Life science Facility (MLF)/Japan-Proton Accelerator Research Complex (J-PARC). The system employs distributed computing via Ethernet, client/server architecture, modular structure and a state machine. Communication between client and server software utilizes socket protocols over TCP/IP. We have deployed this prototype software in the network distributed control system by improving the data acquisition software used at KENS, introducing the system for the SWAN at KENS/KEK. It was kept in working order throughout 2 weeks of machine operation.
    Physica B Condensed Matter 11/2006; 385:1327-1329. DOI:10.1016/j.physb.2006.06.068 · 1.28 Impact Factor
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    ABSTRACT: Ibaraki prefecture materials design diffractometer of J-PARC needs a neutron guide to increase beam intensity without sacrificing measurements of powder diffraction with good resolution, PDF analysis and small angle scattering. Non-parallel guides including elliptical ones have been compared with a linear-straight guide using the McStas simulation. The elliptical guide having the exit focal points away behind the sample position is available to increase the neutron flux at the sample but gives a slight lowering of the instrumental resolution. This elliptical guide gives also Garland peaks at short wavelengths that may give large ambiguities in powder diffraction measurements. Therefore, the linear-straight guide is considered as the best choice for this instrument to keep a good resolution and also a relatively high flux.
    Physica B Condensed Matter 11/2006; 385:1025-1028. DOI:10.1016/j.physb.2006.05.327 · 1.28 Impact Factor
  • Shuki Torii · Atsushi Moriai
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    ABSTRACT: Radial collimators are devices needed to define gauge sizes in neutron diffraction experiments. A design work of collimators needed for an engineering diffractometer that will be built at J-PARC is being progressed. Several collimators for different gauge sizes (1, 3, 5mm, etc …) are going to be designed to define a gauge size range from 1 to 10mm. An equation was established to express a relation between the gauge size and geometrical design parameters of the collimator, by applying a normal distribution curve to the error distribution of measured gauge size. Currently, the geometric calculations for several collimators have been finished. A prototype collimator for a gauge size of 1mm was made and an FWHM (full width at half maximum) of the normal distribution of 1mm was obtained from performance tests conducted at the neutron diffractometer for residual stress analysis RESA in JRR-3 (Japan Research Reactor-3) of Japan Atomic Energy Agency (JAEA). In addition, the performance test results are in a good agreement with results from a Monte Carlo simulation with the McStas using the design parameters.
    Physica B Condensed Matter 11/2006; 385:1287-1289. DOI:10.1016/j.physb.2006.06.052 · 1.28 Impact Factor
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    ABSTRACT: An engineering diffractometer for investigations of stresses and crystallographic structures within engineering components is now being developed at J-PARC project. The diffractometer is designed to view a decoupled-poisoned liquid H2 moderator providing neutrons with good symmetrical diffraction profiles in the acceptable wavelength range. The diffractometer will have a primary flight path of 40m and a secondary flight path of 2.0m for 90° scattering detector banks, and will include a curved supermirror neutron guide to avoid intensity loss due to the long flight path and to reduce backgrounds from fast neutrons and gamma rays. Therefore, stresses with sufficient accuracies in many engineering studies are quite promising. The diffractometer involves a sample translator which is able to handle large and heavy real industrial-scaled components. Detailed design works are being continuously promoted. The optimization of the diffractometer has been performed with a Monte Carlo simulation, and an appropriate resolution of less than 0.2% in Δd/d has been confirmed.
    Physica B Condensed Matter 11/2006; 385:1043-1045. DOI:10.1016/j.physb.2006.05.334 · 1.28 Impact Factor
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    ABSTRACT: An engineering diffractometer designed to solve many problems in materials science and engineering including investigations of stresses and crystallographic structures within engineering components is now being developed at J-PARC project. This instrument views a decoupled-poisoned liquid H 2 moderator providing neutrons with good symmetrical diffraction profiles in the acceptable wavelength range. The primary flight path and the secondary flight path are 40 m and 2.0 m, respectively, for 90 degree scattering detector banks. A curved supermirror neutron guide will be installed to avoid intensity loss due to the long flight path and to reduce backgrounds from fast neutrons and gamma rays. Therefore, stress measurements with sufficient accuracies in many engineering studies are quite promising. The optimization of this instrument has been performed with a Monte Carlo simulation, and an appropriate resolution of less than 0.2 % in δd/d has been confirmed. A prototyped radial collimator to define a gauge width of 1 mm has been designed and manufactured. From performance tests conducted at the neutron diffractometer for residual stress analysis RESA in JRR-3 of Japan Atomic Energy Agency, the normal distribution with a full width at half maximum of 1 mm was obtained in a good agreement with the simulation.
    Materials Science Forum 09/2006; 524:199-204. DOI:10.4028/www.scientific.net/MSF.524-525.199

Publication Stats

115 Citations
55.33 Total Impact Points

Institutions

  • 2002–2015
    • High Energy Accelerator Research Organization
      • Institute of Materials Structure Science
      Tsukuba, Ibaraki, Japan
  • 2012
    • Tohoku University
      • Institute of Multidisciplinary Research for Advanced Materials (IMRAM)
      Miyagi, Japan
  • 2006
    • Japan Atomic Energy Agency
      • Quantum Beam Science Directorate
      Muramatsu, Niigata, Japan
  • 2003
    • Ibaraki University
      Mito-shi, Ibaraki, Japan
    • Okayama University
      • Department of Environmental Chemistry and Materials
      Okayama, Okayama, Japan