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Kamazawa K.,Comprehensive Research Organization for Science and Society CROSS | Ishikado M.,Comprehensive Research Organization for Science and Society CROSS | Ohira-Kawamura S.,Japan Atomic Energy Agency | Kawakita Y.,Japan Atomic Energy Agency | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2017

A powder inelastic neutron-scattering study of HoBaFe4O7 (HBFO) revealed characteristic magnetic excitations associated with geometrical spin frustration. Dispersionless excitations in energy (ω) and wave-vector (Q) space are observed at several discrete energies. Some of them can be attributed to crystal-field excitations of Ho3+ in octahedral symmetry, but the others are explained instead by the vibronic state of the Fe2+ dynamical Jahn-Teller effect with orbit-spin coupling, indicating interaction among the spin, the orbital, and the lattice degree of freedom. The antiferromagnetic HBFO lattice has cubic symmetry, and both Fe2+ and Fe3+ reside on corner-sharing tetrahedra with a number ratio of 3:1. Even though Fe2+ is a Jahn-Teller active ion in tetrahedral symmetry, the system does not exhibit any static lattice distortion to the lowest temperature studied (4 K). The observed excitations can be understood by considering the dynamical interaction among spin-orbital-lattice degrees of freedom, indicating that spin fluctuation due to the frustration effect induces the dynamical Jahn-Teller effect, although in most cases a Jahn-Teller active ion Fe2+ takes the static Jahn-Teller effect in a magnetic oxide system. © 2017 American Physical Society.

Ueda A.,University of Tokyo | Yamada S.,University of Tokyo | Yamada S.,Toho University | Isono T.,University of Tokyo | And 8 more authors.
Journal of the American Chemical Society | Year: 2014

A hydrogen bond (H-bond) is one of the most fundamental and important noncovalent interactions in chemistry, biology, physics, and all other molecular sciences. Especially, the dynamics of a proton or a hydrogen atom in the H-bond has attracted increasing attention, because it plays a crucial role in (bio)chemical reactions and some physical properties, such as dielectricity and proton conductivity. Here we report unprecedented H-bond-dynamics-based switching of electrical conductivity and magnetism in a H-bonded purely organic conductor crystal, κ-D3(Cat-EDT-TTF)2 (abbreviated as κ-D). This novel crystal κ-D, a deuterated analogue of κ-H3(Cat-EDT-TTF)2 (abbreviated as κ-H), is composed only of a H-bonded molecular unit, in which two crystallographically equivalent catechol-fused ethylenedithiotetrathiafulvalene (Cat-EDT-TTF) skeletons with a +0.5 charge are linked by a symmetric anionic [O⋯D⋯O]-1-type strong H-bond. Although the deuterated and parent hydrogen systems, κ-D and κ-H, are isostructural paramagnetic semiconductors with a dimer-Mott-type electronic structure at room temperature (space group: C2/c), only κ-D undergoes a phase transition at 185 K, to change to a nonmagnetic insulator with a charge-ordered electronic structure (space group: P1̄). The X-ray crystal structure analysis demonstrates that this dramatic switching of the electronic structure and physical properties originates from deuterium transfer or displacement within the H-bond accompanied by electron transfer between the Cat-EDT-TTF π-systems, proving that the H-bonded deuterium dynamics and the conducting TTF π-electron are cooperatively coupled. Furthermore, the reason why this unique phase transition occurs only in κ-D is qualitatively discussed in terms of the H/D isotope effect on the H-bond geometry and potential energy curve. © 2014 American Chemical Society.

Medarde M.,Paul Scherrer Institute | Mena M.,Paul Scherrer Institute | Gavilano J.L.,Paul Scherrer Institute | Pomjakushina E.,Paul Scherrer Institute | And 9 more authors.
Physical Review Letters | Year: 2013

We report the observation of a stepwise "melting" of the low-temperature Na-vacancy order in the layered transition-metal oxide Na 0.7CoO2. High-resolution neutron powder diffraction analysis indicates the existence of two first-order structural transitions, one at T1≈290 K followed by a second at T2≈400 K. Detailed analysis strongly suggests that both transitions are linked to changes in the Na mobility. Our data are consistent with a two-step disappearance of Na-vacancy order through the successive opening of first quasi-1D (T 1>T>T2) and then 2D (T>T2) Na diffusion paths. These results shed new light on previous, seemingly incompatible, experimental interpretations regarding the relationship between Na-vacancy order and Na dynamics in this material. They also represent an important step towards the tuning of physical properties and the design of tailored functional materials through an improved control and understanding of ionic diffusion. © 2013 American Physical Society.

Sugiyama J.,Toyota Central R&D Labs. | Nozaki H.,Toyota Central R&D Labs. | Harada M.,Toyota Central R&D Labs. | Kamazawa K.,Toyota Central R&D Labs. | And 9 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

In order to study the diffusive nature of lithium transition-metal phospho-olivines, we measured muon-spin relaxation (μ +SR) spectra for the polycrystalline LiMPO 4 samples with M=Mn, Fe, Co, or Ni in the temperature range between 50 and 500 K. The μ +SR spectra under zero applied field are strongly affected by the magnetic moments of the 3d electrons in the M2 + ions so that, for LiMnPO 4, it was difficult to detect the relaxation change caused by the diffusion due to the large Mn2 +(S=5/2) moments. However, diffusive behavior was clearly observed via the relaxation due to nuclear dipolar fields above ∼150 K for LiFePO 4, LiCoPO 4, and LiNiPO 4 as S decreased from 2 to 1. From the temperature dependence of the nuclear field fluctuation rate, self-diffusion coefficients of Li + ions (D Li) at 300 K and its activation energy (E a) were estimated, respectively, as ∼3.6(2)×10 -10 cm2/s and E a=0.10(2) eV for LiFePO 4, ∼1.6(1)×10 -10 cm2/s and E a=0.10(1) eV for LiCoPO 4, and ∼2.7(4)×10 -10 cm2/s and E a=0.17(2) eV for LiNiPO 4, assuming that the diffusing Li + ions jump between the regular site and interstitial sites. © 2012 American Physical Society.

Nyuta K.,Tokyo University of Science | Yoshimura T.,Nara Women's University | Tsuchiya K.,Tokyo University of Science | Sakai H.,Tokyo University of Science | And 3 more authors.
Journal of Colloid and Interface Science | Year: 2012

The aggregation behavior in aqueous solution of zwitterionic heterogemini surfactants, N,N-dimethyl-N-[2-(N'-alkyl-N'-β-carboxypropanoylamino)ethyl]-1-alkylammonium bromides (2C nAmCa, in which n represents hydrocarbon chain lengths of 8, 10, 12, and 14), with nonidentical headgroups containing ammonium and carboxylate was investigated through small-angle neutron scattering (SANS), dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM) techniques. We found that the aggregation behavior of 2C nAmCa strongly depended on the hydrocarbon chain length and the surfactant concentration. 2C 8AmCa forms spherical micelles with radius of approximately 2nm in solution. 2C 10AmCa forms rod-like micelles at low concentration in the solution, and the structure changes to vesicles with increasing concentration. The membrane thickness of the vesicle is independent of the surfactant concentration. Aggregation shape transitions were also observed for 2C 12AmCa. In addition, it appears that the vesicles of 2C 12AmCa coexist with the rod-like micelles at a wide range of surfactant concentrations. Interestingly, 2C 14AmCa forms vesicles with averaged membrane thickness of 2.32nm in solution, even at the extremely low concentration of 10 times the cmc. Thus, it was concluded that 2C nAmCa exhibits unique aggregation behavior, such as the formation of spherical micelle→rod-like micelle→rod-like micelle+vesicle (coexistence)→vesicle with increasing hydrocarbon chain length and surfactant concentration. We also found that the membrane structure is an interdigitated bilayer when the vesicles are formed. This formation of interdigitated structures is related to the origins of the effective properties of 2C nAmCa in solution. © 2011 Elsevier Inc.

Isono T.,University of Tokyo | Kamo H.,University of Tokyo | Ueda A.,University of Tokyo | Takahashi K.,Kobe University | And 6 more authors.
Nature Communications | Year: 2013

Purely organic materials are generally insulating. Some charge-carrier generation, however, can provide them with electrical conductivity. In multi-component organic systems, carrier generation by intermolecular charge transfer has given many molecular metals. By contrast, in purely organic single-component systems, metallic states have rarely been realized although some neutral-radical semiconductors have been reported. Here we uncover a new type of purely organic single-component molecular conductor by utilizing strong hydrogen-bonding interactions between tetrathiafulvalene-based electron-donor molecules. These conductors are composed of highly symmetric molecular units constructed by the strong intra-unit hydrogen bond. Moreover, we demonstrate that, in this system, charge carriers are produced by the partial oxidation of the donor molecules and delocalized through the formation of the symmetric intra-unit hydrogen bonds. As a result, our conductors show the highest room-temperature electrical conductivity and the metallic state under the lowest physical pressure among the purely organic single-component systems, to our knowledge. © 2013 Macmillan Publishers Limited. All rights reserved.

Sugiyama J.,Toyota Central R&D Labs. | Mansson M.,ETH Zurich | Ofer O.,TRIUMF Laboratory Particle and Nuclear Physics | Kamazawa K.,Toyota Central R&D Labs. | And 11 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The presence of antiferromagnetic (AF) order seems to be a common feature for the parent compounds of cuprate as well as some pnictide high-temperature superconductors. In order to search for antiferromagnetic order in the closely related rare-earth cobalt arsenic oxides (RCoAsO), we have measured muon-spin rotation and relaxation (μ+SR) spectra on a series of powder samples with R=La, Ce, Pr, Nd, Sm, and Gd. It was found that, besides GdCoAsO, all the other five compounds enter into a static ferromagnetic ordered phase below around 70 K (=TC), while additional transitions into a static AF ordered phase were found for NdCoAsO and SmCoAsO. For GdCoAsO, a static ferrimagnetic phase appeared below 60.5 K and then an incommensurate spin-density-wave ordered phase followed below 3.2 K. The AF spin structure was also found to strongly depend on R. © 2011 American Physical Society.

Fujita S.,Toyota Central R&D Labs. | Kamazawa K.,Toyota Central R&D Labs. | Kamazawa K.,Comprehensive Research Organization for Science and Society CROSS | Yamamoto S.,Toyota Central R&D Labs. | And 6 more authors.
Journal of Physical Chemistry C | Year: 2013

Highly dense sulfonic acid-functionalized mesoporous electrolytes with high proton conductivity under dry conditions were prepared using tetramethoxysilane and 3-mercaptopropyltrimethoxysilane in the presence of surfactants. Impedance spectroscopy and quasielastic neutron scattering measurements showed that the proton conductive properties of the mesoporous electrolytes depended significantly on the sulfonic acid densities on the surface of the mesoporous walls. This finding was also supported by molecular dynamics simulations. The proton conductivity of the mesoporous electrolyte with the highest acid density of 3.1 SO3H molecules/nm2 showed a value of 0.3 mS/cm at 433 K even under dry conditions. This value was higher than that for Nafion by about 2 orders of magnitude. Such high proton conductivity is thought to be induced by proton hopping in the hydrogen-bonded networks that were predominantly formed by neighboring sulfonic acid groups. © 2013 American Chemical Society.

Abe J.,Comprehensive Research Organization for Science and Society CROSS | Sekine K.,Japan Oil, Gas and Metals National Corporation | Harjo S.,Japan Atomic Energy Agency | Gong W.,Japan Atomic Energy Agency | Aizawa K.,Japan Atomic Energy Agency
Materials Science Forum | Year: 2014

Acoustic emission (AE) is defined as a transient elastic wave generated by the rapid release of energy within a material. Crack initiation, phase transition and rupturing in rock materials are all detectable with the measurement of AE signals, and therefore such measurement helps to understand the underlying mechanism(s) of macroscopic deformation. In this study of the deformation mechanism(s) of rock samples, simultaneous measurements of the neutron diffraction pattern and AE signals were performed using the Engineering Materials Diffractometer "TAKUMI" at the Japan Proton Accelerator Research Complex (J-PARC). Two types of rock sample were tested in the experiments: sandstone and carbonate rock. A discrepancy was found between macroscopic strain (measured by strain gauge) and lattice strain (measured by neutron diffraction), and AE signals that would be generated by grain slip and pore collapse in rock samples were detected. Macroscopic strain in the rock samples was associated not only with lattice strain but also with mineral grain slip and pore collapse within the rock. The combination of AE signal measurements and neutron diffraction is an effective tool for investigating the deformation mechanisms of rock materials. © (2014) Trans Tech Publications, Switzerland.

PubMed | Ibaraki University and Comprehensive Research Organization for Science and Society CROSS
Type: | Journal: Talanta | Year: 2015

2-(2-Hydroxyphenyl)benzimidazole derivatives (X-HBIs), modified by various substituents X (X=H, CH3, OH, OCH3, NO2, NHCOCH3, NH2, N(CH3)2), were synthesized and their fluorescent behaviors and equilibriums in aqueous solution were studied. Strong fluorescence attributed to the tautomer emission was observed in aqueous solution at pH 7.4. The fluorescence intensities of the X-HBIs were enhanced selectively by addition of Zn(2+) but not by addition of Na(+), K(+), Mg(2+), Ca(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), and Cu(2+). Additionally, the effective ratiometric fluorescence response to Zn(2+) addition was observed in 5-NH2-HBI and 5-N(Me)2-HBI. The pH-titration and speciation studies proved that the X-HBIs have two or three protonation equilibriums and one complexation equilibrium corresponding to the formation of the [Zn(X-HBI)](+) complex. Further structural studies using extended X-ray absorption fine structure analyses and density functional theory calculations identified the dominant Zn(2+) species as the [Zn(HBI)(H2O)3](+) complex in aqueous solution. Based on the substituent effect on the fluorescence properties of X-HBIs and their Zn(2+) complexes in aqueous solution, the maximum fluorescence excitation and fluorescence wavelengths of both the tautomeric form and the Zn(2+) complexes were dependent on the Hammett substituent constants of X, which was attributed to the change of the -* energy gap of HBI by introduction of the substituent.

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