Browsing by Author "Ishikawa, Y"

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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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    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)