Browsing by Author "Watanabe, M"

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    Microscopic solvation structure and phase behavior of thermo-responsive polymers in ionic liquids
    (International Conference on Neutron Scattering, 2017-07-12) Hirosawa, K; Fujii, K; Ueki, T; Kitazawa, Y; Watanabe, M; Gilbert, EP; Shibayama, M
    Ionic liquids (ILs) are molten salts having their melting points near room temperature. ILs consist of only ion species, and thus they exhibit unique solvent properties such as high ion conductivity, negligible volatility and nonflammability. Recently,it was reported that poly(benzyl methacrylate) (PBnMA) and its derivatives show a lower critical solution temperature type phase separation in ILs. Interestingly, the phase separation temperature of the thermo-responsive polymers in IL systems strongly depends on both chemical structures of the polymer and the ILs. It indicates that macroscopic phase behavior of the systems is strongly affected by microscopic molecular interactions between polymers and ILs. In this study, we performed small-angle neutron scattering (SANS) experiments on various PBnMA derivatives in deuterated IL solutions. The interaction parameter, ? between the polymers and the ILs was estimated from the obtained SANS profiles. Here, enthalpic (?H) and entropic (?S) contributions to ? were obtained from temperature dependence of ?. As a result, it was found that ?H strongly depends on the chemical structure of the polymers and the ILs. Furthermore, microscopic solvation structure of the polymers in IL systems was investigated by high-energy X-ray total scattering measurement with the aid of molecular dynamics (MD) simulations. It was found that there is strong correlation between the value of ?H and the microscopic solvation structure.
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    New Zealand's most easterly palaeotsunami deposit confirms evidence for major trans-Pacific event
    (Elsevier, 2018-11-01) Goff, JR; Goto, K; Chagué, C; Watanabe, M; Gadd, PS; King, DN
    Sedimentary, geochemical, geomorphological, radiocarbon and numerical modelling data were used to examine the nature, extent and age of a boulder scatter at Okawa Point, Chatham Island, New Zealand. Boulders up to 98 t were traced around 800 m inland and comprised both a landward and seaward grouping on either side of a mid-Holocene high-stand storm ridge dated to around 4840–4810 cal BP. The landward boulder scatter was linked with an enigmatic coarse sand/gravel layer that extends up to 1100 m inland and has been dated to around 3500–4500 cal BP. Numerical modelling indicated that while the seaward boulders that mainly rest upon the Chatham Island Schist shore platform could have been emplaced by either storm or tsunami waves, those landward of the mid-Holocene storm ridge were most probably transported by a tsunami. There are several near-contemporaneous palaeotsunami deposits reported from mainland New Zealand, Australia, SW Pacific and the wider Pacific region. If some or all of these are associated with the same basin-wide palaeotsunami then it appears likely to have been one of the largest Holocene Pacific palaeotsunamis. An analysis of historical and numerically modelled data suggests that the most likely candidate is from within the northern Chile seismic gap, with early evidence suggesting that a large palaeoseismic and palaeotsunami event may have occurred around 4000 yr BP. If correct, this has important implications for assessing the largest possible magnitude earthquakes in the northern Chile seismic gap and the size of the tsunamis they generate. © 2018 Elsevier B.V.
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    Quantum magnetic properties of the spin-1/2 triangular-lattice antiferromagnet Ba2La2CoTe2O12
    (American Physical Society, 2018-11-05) Kojima, Y; Watanabe, M; Kurita, N; Tanaka, H; Matsuo, A; Kindo, K; Avdeev, M
    We report the crystal structure of Ba2La2CoTe2O12 determined by Rietveld analysis using x-ray powder-diffraction data. It was found from magnetic measurements that Ba2La2CoTe2O12 can be described as a spin-12 triangular-lattice antiferromagnet with easy-plane anisotropy at low temperatures. This compound undergoes a magnetic phase transition at TN=3.26K to an ordered state with the 120∘ structure. The magnetization curve exhibits the one-third plateau characteristic of triangular-lattice quantum antiferromagnets. The antiferromagnetic exchange interaction and the g factors parallel and perpendicular to the c axis were evaluated to be J/kB=22K,g∥=3.5, and g⊥=4.5, respectively. ©2018 American Physical Society
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    Successive phase transitions and magnetization plateau in the spin-1 triangular-lattice antiferromagnet Ba2La2NiTe2O12 with small easy-axis anisotropy
    (American Physical Society, 2019-08-22) Saito, M; Watanabe, M; Kurita, N; Matsuo, A; Kindo, K; Avdeev, M; Jeschke, HO; Tanaka, H
    The crystal structure and magnetic properties of the spin-1 triangular-lattice antiferromagnet Ba2La2NiTe2O12 are reported. Its crystal structure is trigonal R¯3, which is the same as that of Ba2La2NiW2O12 [Y. Doi et al., J. Phys.: Condens. Matter 29, 365802 (2017)]. However, the exchange interaction J/kB≃19 K is much greater than that observed in the tungsten system. At zero magnetic field, Ba2La2NiTe2O12 undergoes successive magnetic phase transitions at TN1=9.8 K and TN2=8.9 K. The ground state is accompanied by a weak ferromagnetic moment. These results indicate that the ground-state spin structure is a triangular structure in a plane perpendicular to the triangular lattice owing to the small easy-axis-type anisotropy. The magnetization curve exhibits the one-third plateau characteristic of a two-dimensional triangular-lattice Heisenberg-like antiferromagnet. Exchange constants are also evaluated using density functional theory (DFT). The DFT results demonstrate the large difference in the exchange constants between tellurium and tungsten systems and the good two-dimensionality of the tellurium system. ©2019 American Physical Society