Browsing by Author "Sakuma, T"

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    Crystal structure of R10Mo6O33 (R = Nd, Pr) from 3 K to 973 K by neutron powder diffraction
    (Elsevier, 2016-05-01) Ishikawa, Y; Danilkin, SA; Avdeev, M; Voronkova, VI; Sakuma, T
    Oxygen ionic conductors, R10Mo6O33 (R = Nd, Pr), were investigated by neutron powder diffraction in the wide temperature range from 3 K to 973 K. The Rietveld analyses and peak profile examination confirmed that there are no structural phase transitions in whole temperature range, keeping a cubic structure. The nuclear density distribution calculated by maximum entropy method and the Bond Valence Sum mapping analysis shows that a possible diffusion pathway connects the neighboring 48i oxygen ions at general positions. These results are consistent with the previous results of a one-particle Coulomb potential calculation and electric conductivity measurements. © 2015 Elsevier B.V.
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    Derivation of inter-atomic force constants of Cu2O from diffuse neutron scattering measurement
    (Atom Indonesia, 2013-04-15) Makhsun, T; Sakuma, T; Kartini, E; Takahashi, H; Igawa, N; Danilkin, SA; Sakai, R
    Neutron scattering intensity from Cu2O compound has been measured at 10 K and 295 K with High Resolution Powder Diffractometer at JRR-3 JAEA. The oscillatory diffuse scattering related to correlations among thermal displacements of atoms was observed at 295 K. The correlation parameters were determined from the observed diffuse scattering intensity at 10 and 295 K. The force constants between the neighboring atoms in Cu2O were estimated from the correlation parameters and compared to those of Ag2O. (c) 2016 Atom Indonesia.
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    Estimation of force constants of Al from diffuse neutron scattering measurement
    (The Physical Society of Japan, 2014-06-19) Makhsun; Hashimoto, T; Takahashi, H; Kamishima, O; Igawa, N; Danilkin, SA; Sakuma, T
    Neutron diffraction measurement of an aluminum powder sample at 290 K was carried out at the high resolution powder diffractometer installed at JRR-3. Broad oscillations of the diffuse scattering intensity were observed and explained by the correlation effects among the thermal displacements of atoms. The interatomic force constants were determined from the correlation effects using a newly introduced equation. The derived force constants and the crystal structure of Al were used to estimate the phonon dispersion relations, phonon density of states, and specific heat by computer simulation. The calculated phonon dispersion relations and specific heat of Al are similar to those obtained from inelastic neutron scattering and specific heat measurements, respectively.© 2014, The Physical Society of Japan.
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    Inter-atomic force constants of Ag2O from diffuse neutron scattering measurement
    (Elsevier Science BV., 2012-10-04) Wada, T; Sakuma, T; Sakai, R; Uehara, H; Xianglian; Takahashi, H; Kamishima, O; Igawa, N; Danilkin, SA
    Diffuse neutron scattering measurements have been performed on powder Ag(2)O at 8 and 295 K with the use of High Resolution Powder Diffractometer installed at JRR-3 in Japan Atomic Energy Agency. Oscillatory diffuse scattering intensities are clearly observed at 8 and 295 K. The observed diffuse scattering intensities are explained by including the correlation effects among thermal displacements of atoms. The force constants among neighboring atoms in Ag(2)O are obtained from the values of correlation effects and Debye-Waller temperature parameters at 295 K. © 2012, Elsevier Ltd.
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    Neutron diffraction study of diffuse scattering in Cu2−δSe superionic compounds
    (Elsevier, 2011-05-05) Danilkin, SA; Avdeev, M; Sakuma, T; Macquart, RB; Ling, CD
    Crystal structure and short-range order in Cu2-delta Se compounds were studied in superionic and non-superionic phases using high-resolution neutron diffractometer Echidna at ANSTO. In diffraction patterns of beta-Cu-1.98 Se (ordered phase at ambient T), both Bragg peaks and diffuse background change sharply through the beta -> alpha structural phase transition at T = 414K during heating. In case of alpha-Cu1.75Se (disordered superionic phase at ambient T) the changes are monotonic, showing gradual shifts of Bragg peaks and increased intensity of the diffuse background as a function of temperature. On cooling, both compounds undergo a beta -> beta ' transformation. Diffuse scattering in the alpha-phase shows an oscillating dependence on wavevector, with broad peaks centred at Q similar to 3, 5.5 and 8 angstrom(-1). The measurements taken in energy dispersive mode show that the oscillating diffuse background arises from correlated thermal displacements of the ions. Diffuse scattering is higher for compositions close to stoichiometry and increases with temperature. Theoretical calculations show that the increase in diffuse intensity both with temperature and Cu content is related to correlated thermal vibrations of Se and Cu atoms, with Se-Cu(8c, 32f) and Cu(8c)-Cu(8c) correlations being the most important. (C) 2011 Elsevier B.V.
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    Neutron scattering study of ionic diffusion in Cu–Se superionic compounds
    (Elsevier Science BV, 2012-10-04) Danilkin, SA; Avdeev, M; Sale, M; Sakuma, T
    Paper reports the results of the neutron scattering study of crystal structure and diffusion of Cu2 − δSe compounds in superionic α-phase. We found that the crystallographic model with Cu atoms in the 8c (0.25, 0.25, 0.25) and 32f (x, x, x) (x = 0.33–0.39) sites in fluorite lattice provides the best description of the average structure. The quasi-elastic neutron scattering data reveal the decrease of the self-diffusion coefficient with the deviation from the stoichiometry due to the longer residence time of Cu atoms between diffusion hops. Combination of neutron diffraction, quasi-elastic scattering experimental data with the Bond-Valence Method simulations strongly suggests that the Cu atoms diffuse between the nearest 8c sites through the 32f sites. © 2012, Elsevier Ltd.
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    Neutron scattering study of short-range correlations and ionic diffusion in copper selenide
    (Springer, 2011-02-01) Danilkin, SA; Avdeev, M; Sakuma, T; Macquart, RB; Ling, CD; Russina, M; Izaola, Z
    The paper reports the results of a neutron scattering study of Cu(2-delta)Se superionic compounds. The crystallographic model fitted to the diffraction data shows the occupation of 8c and 32f sites by Cu atoms. Observed diffuse background is related to correlated thermal vibrations of Se and Cu atoms, with Sea dagger"Cu (8c,32f) and Cu (8c)a dagger"Cu (8c) correlations being most important. The quasi-elastic neutron experiments show the decrease of the self-diffusion coefficient with the deviation from the stoichiometry due to the longer residence time of Cu ions between diffusion hops. Combination of neutron diffraction, diffuse scattering and quasi-elastic scattering experimental data suggests that the Cu atoms diffuse between the nearest 8c sites through the 32f sites. © 2011, Springer.
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    Pressure dependence of crystal structure of Cu2O by TOF powder neutron diffraction
    (Elsevier, 2014-09-01) Ishikawa, Y; Sakuma, T; Takahashi, H; Danilkin, SA
    Neutron diffraction measurements were performed on powder Cu2O with different samples that are pressure released after a pressing force of 295 K with iMATERIA (IBARAKI Materials Designed Diffractometer) installed at MLF in J-PARC. Peak widths of Bragg lines increased depending on the pressing force. To clarify the relation between the crystallite size and the microstrain effect, Rietveld refinement analysis on a TOF neutron diffraction pattern of Cu2O was performed by assuming a cubic cuprite type structure (space group Pn-3m). Strain and crystallite size effects were estimated from Lorentzian terms in the Pseudo-Voigt profile function with a pair of Back-to-Back exponential types based on the Stephenes model. It is considered that the increasing peak width according to the dependence of pressing force is mainly derived from strain effects. And this result is consistent with the previous studies of Ag2O where the Williamson–Hall plot method by X-ray diffraction was applied. © 2013, Elsevier B.V.
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    Thermal expansion properties of Ag2O crystal structure by powder neutron diffraction
    (The Physical Society of Japan, 2015-7-12) Ishikawa, Y; Danilkin, SA; Avdeev, M; Kamiyama, T; Sakuma, T
    Thermal expansion property of Silver(I)-Oxide (Ag2O) was structurally investigated by neutron powder diffraction from 3 to 400 K, and measured by X-ray powder diffraction from 20 to 498 K. Temperature dependency of lattice parameter by neutron diffraction indicates the negative thermal expansion (NTE) below room temperature, and it changes to positive thermal expansion (PTE) from 300 to 400 K. And this result is consistent with X-ray diffraction and TMA measurement. Moreover, the result by X-ray diffraction shows that lattice parameter significantly decreases above 400 K. Since the result by TG measurement shows the mass loss remarkably in this temperature region, it is considered that decreasing lattice parameter above 400 K is caused from thermal decomposition. ©2015 The Physical Society of Japan, Creative Commons Attribution 4.0 (CC-BY 4.0)