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Ikeda, Kazutaka*; Sashida, Sho*; Otomo, Toshiya*; Oshita, Hidetoshi*; Honda, Takashi*; Hawai, Takafumi*; Saito, Hiraku*; Ito, Shinichi*; Yokoo, Tetsuya*; Sakaki, Koji*; et al.
International Journal of Hydrogen Energy, 51(Part A), p.79 - 87, 2024/01
Times Cited Count：0 Percentile：0.01(Chemistry, Physical)Sakaki, Koji*; Kim, H.*; Majzoub, E. H.*; Machida, Akihiko*; Watanuki, Tetsu*; Ikeda, Kazutaka*; Otomo, Toshiya*; Mizuno, Masataka*; Matsumura, Daiju; Nakamura, Yumiko*
Acta Materialia, 234, p.118055_1 - 118055_10, 2022/08
Times Cited Count：9 Percentile：83.6(Materials Science, Multidisciplinary)
as the origin of volume collapseYu, R.*; Hojo, Hajime*; Watanuki, Tetsu; Mizumaki, Masaichiro*; Mizokawa, Takashi*; Oka, Kengo*; Kim, H.*; Machida, Akihiko; Sakaki, Koji*; Nakamura, Yumiko*; et al.
Journal of the American Chemical Society, 137(39), p.12719 - 12728, 2015/10
Times Cited Count：34 Percentile：70.17(Chemistry, Multidisciplinary)no abstracts in English
Sn
by time resolved X-ray diffractionMachida, Akihiko; Higuchi, Kensuke*; Katayama, Yoshinori; Sakaki, Koji*; Kim, H.*; Nakamura, Yumiko*
Nihon Kinzoku Gakkai-Shi, 79(3), p.124 - 130, 2015/03
Times Cited Count：4 Percentile：22.77(Metallurgy & Metallurgical Engineering)Structural changes on hydrogen absorption process of hydrogen absorbing alloy LaNiSn have been investigated by time-resolved X-ray diffraction measurements using synchrotron radiation source. We have found the transient intermediate phase between the solid solution and hydride phases of LaNiSn under non-equilibrium hydrogen pressure condition at room temperature. LaNiSn has transformed into the hydride through three phase co-existing state. The hydrogen content of the intermediate phase estimated from the unit cell volume is independent of the induced hydrogen gas pressure. The variation of lattice constants indicate that the hydrogen atoms are located at the La
Ni(Ni,Sn) octahedron and La(Ni,Sn) tetrahedron in the intermediate phase.
(Fe
Mn
)
(
, 
)Sakaki, Koji*; Kim, H.*; Machida, Akihiko; Watanuki, Tetsu; Nakamura, Yumiko*
Nihon Kinzoku Gakkai-Shi, 79(3), p.112 - 117, 2015/03
Times Cited Count：3 Percentile：17.9(Metallurgy & Metallurgical Engineering)no abstracts in English
Ti
Zr
Kim, H.*; Sakaki, Koji*; Asano, Kota*; Ikeda, Kazutaka*; Otomo, Toshiya*; Machida, Akihiko; Watanuki, Tetsu; Nakamura, Yumiko*
Nihon Kinzoku Gakkai-Shi, 79(3), p.131 - 136, 2015/03
Times Cited Count：0 Percentile：0.01(Metallurgy & Metallurgical Engineering)no abstracts in English
PrNi
by Changing Mg/Pr ratioSakaki, Koji*; Terashita, Naoyoshi*; Kim, H.*; Majzoub, E. H.*; Proffen, T.*; Machida, Akihiko; Watanuki, Tetsu; Tsunokake, Shigeru*; Nakamura, Yumiko*; Akiba, Etsuo*
Sumato Purosesu Gakkai-Shi, 3(6), p.359 - 366, 2014/11
no abstracts in English
Ti
during hydrogen cyclingKim, H.*; Sakaki, Koji*; Saita, Itoko*; Enoki, Hirotoshi*; Noguchi, Kazuo*; Machida, Akihiko; Watanuki, Tetsu; Nakamura, Yumiko*
International Journal of Hydrogen Energy, 39(20), p.10546 - 10551, 2014/07
Times Cited Count：13 Percentile：32.39(Chemistry, Physical)The effect of the vanadium content on the cyclic stability of V-Ti binary alloys was investigated. VTi, 
0.2 and 0.5 samples were hydrogenated and dehydrogenated at 410 K and 553 K respectively, for more than 100 times. During hydrogen cycling, reduction in the reversible hydrogen storage capacity was clearly observed from both samples. In addition, the shape of the pressure-composition-isotherm curves was significantly altered over the testing cycle period; the absorption and desorption plateaus got markedly inclined and the hysteresis became evidently smaller. We found that even after the hydrogen storage capacity of VTi was significantly reduced, at low enough temperature VTi was able to absorb hydrogen as much as it did at the first cycle.
PrNi
(
= 0.6 and 1.0)Sakaki, Koji*; Terashita, Naoyoshi*; Kim, H.*; Majzoub, E. H.*; Machida, Akihiko; Watanuki, Tetsu; Tsunokake, Shigeru*; Nakamura, Yumiko*; Akiba, Etsuo*
Journal of Physical Chemistry C, 118(13), p.6697 - 6705, 2014/04
Times Cited Count：21 Percentile：55.49(Chemistry, Physical)We present an investigation of the degradation mechanism against hydrogenation cycles in MgPrNi ( = 0.6 and 1.0). Mg
PrNi shows significant degradation and loss of capacity after only a few cycles, while Mg
Pr
Ni did not show any reduction of hydrogen storage capacity until 100 cycles. The peak broadening of X-ray diffraction patterns and accumulation of lattice strain were observed concomitantly with an increase of hydrogenation cycles only in MgPrNi. These changes were not observed in MgPrNi. In pair distribution function patterns, 
-dependent peak broadening was observed and it became significant with an increasing number of cycles in MgPrNi, suggesting an increase of the dislocation density. MgPrNi showed higher hardness and more pulverization upon hydrogenation than MgPrNi.
Fe M
ssbauer spectroscopy of RFe (R = Y, Gd) hydrides synthesized under ultra-high-pressure hydrogenMitsui, Takaya; Masuda, Ryo*; Seto, Makoto; Hirao, Naohisa*; Matsuoka, Takehiro*; Nakamura, Yumiko*; Sakaki, Koji*; Enoki, Hirotoshi*
Journal of Alloys and Compounds, 580(Suppl.1), p.S264 - S267, 2013/12
Times Cited Count：8 Percentile：42.73(Chemistry, Physical)Ti alloys from the atomic pair distribution function analysisKim, H.*; Sakaki, Koji*; Ogawa, Hiroshi*; Nakamura, Yumiko*; Nakamura, Jin*; Akiba, Etsuo*; Machida, Akihiko; Watanuki, Tetsu; Proffen, T.*
Journal of Physical Chemistry C, 117(50), p.26543 - 26550, 2013/12
Times Cited Count：41 Percentile：75.8(Chemistry, Physical)Reduction in reversible hydrogen storage capacity with increasing hydrogenation and dehydrogenation cycle number is observed in numerous hydrogen storage materials, but the mechanism behind this unfavorable change has not been elucidated yet. In this study, we have investigated the development of structural defects or disorders in VTiH
, = 0, 0.2, and 0.5, during the first 15 hydrogen absorption and desorption cycles using the atomic pair distribution function (PDF) analysis of synchrotron X-ray total scattering data to find out the possible structural origin of the poor cyclic stability of VTi alloys.
ssbauer study using synchrotron radiationMasuda, Ryo; Mitsui, Takaya; Ito, Keiji*; Sakaki, Koji*; Enoki, Hirotoshi*; Nakamura, Yumiko*; Seto, Makoto
Hyperfine Interactions, 204(1-3), p.139 - 142, 2012/03
Times Cited Count：2 Percentile：76.72(Physics, Atomic, Molecular & Chemical)We have been developing a system for in situ Mssbauer studies using synchrotron radiation (SR) to elucidate the mechanism of hydrogenation processes. In the system, samples reacts in an atmosphere chamber and SR-based Mssbauer spectra using variable-frequency nuclear monochromator and energy spectra of inelastic nuclear resonant scattering (NRS) of SR are measured. As a feasibility study, the temperature dependence of the Mssbauer and inelastic NRS spectra of Fe in 
-GdFeH
under vacuum were measured. In both spectra, clear differences were observed between 373 K and 573 K. These differences can be interpreted by the change of microscopic environment around Fe at the dehydrogenation. Thus, it is confirmed that this system works well enough to perform the in-situ Mssbauer study on the dehydrogenation of -GdFeH.
Ito, Kenji*; Oka, Toshitaka*; Kobayashi, Yoshinori*; Shirai, Yasuharu*; Wada, Kenichiro*; Matsumoto, Masataka*; Fujinami, Masanori*; Hirade, Tetsuya; Honda, Yoshihide*; Hosomi, Hiroyuki*; et al.
Materials Science Forum, 607, p.248 - 250, 2009/00
So far no standard procedure for the positron annihilation lifetime (PAL) technique has been established. A lack of the standards has led to difficulty in ensuring the equivalency and reliability of data from different laboratories. As a first, we conducted an interlaboratory comparison of PAL measurements for metal, polymer and silica glass with agreed procedures for data recording and analysis. The PAL data recorded at different laboratories were analyzed with a single lifetime component for the metal sample and with three components for the others, respectively. Based on the results of the reported positron and ortho-positronium lifetimes, the possible sources of the uncertainties in the PAL measurements are discussed. To reduce the effect of scattered 
rays, a lead shield was placed between the detectors. The uncertainty was significantly decreased, signifying that placing lead shields between the detectors effectively reduced the false signals due to the scattered rays.
Ito, Kenji*; Oka, Toshitaka*; Kobayashi, Yoshinori*; Shirai, Yasuharu*; Wada, Kenichiro*; Matsumoto, Masataka*; Fujinami, Masanori*; Hirade, Tetsuya; Honda, Yoshihide*; Hosomi, Hiroyuki*; et al.
Journal of Applied Physics, 104(2), p.026102_1 - 026102_3, 2008/07
Times Cited Count：48 Percentile：83.5(Physics, Applied)Interlaboratory comparison of positron annihilation lifetime measurements using synthetic fused silica and polycarbonate was conducted with the participation of 12 laboratories. By regulating procedures for the measurement and data analysis the uncertainties of the positron lifetimes obtained at different laboratories were significantly reduced in comparison with those reported in the past.
; *; *; ; *; Yoshikawa, Hiroshi; ; Sakaki, Hironao; *; Yokomizo, Hideaki
JAERI-M 94-078, 29 Pages, 1994/06
no abstracts in English
Kobayashi, Yoshinori*; Ito, Kenji*; Oka, Toshitaka*; Sakaki, Koji*; Shirai, Yasuharu*; Honda, Yoshihide*; Shimazu, Akira*; Fujinami, Masanori*; Hirade, Tetsuya; Saito, Haruo*; et al.
no journal, ,
For making a standard sample of positron annihilation measurement, quartz glass and polycarbonate were measured with 12 apparatus at AIST, Chiba Univ., Tokyo Univ., Tsukuba Univ., Touhoku Univ., Tokyo Gakugei Univ. JAEA, Nitto Denko, and Toray Research Center. By regulating procedure for the measurement and data analysis the uncertainties of the positron annihilation lifetime obtained at different laboratories were significantly reduced.
Ito, Kenji*; Oka, Toshitaka*; Kobayashi, Yoshinori*; Shirai, Yasuharu*; Wada, Kenichiro*; Matsumoto, Masataka*; Fujinami, Masanori*; Hirade, Tetsuya; Honda, Yoshihide*; Hosomi, Hiroyuki*; et al.
no journal, ,
So far no standard procedure for the positron annihilation lifetime (PAL) technique has been established. A lack of the standards has led to difficulty in ensuring equivalency and reliability of data from different laboratories. Recently, as a first step toward the standardization of the PAL technique, we conducted an interlaboratory comparison of PAL measurements for fused silica, polycarbonate and metal with agreed procedures for data recording and analysis. Based on the results of the reported lifetimes, possible sources of the uncertainties in the PAL measurements is probably caused by the backscattered -rays by other detectors. We succeeded to show that inserting shields between detectors can reduce the uncertainty.
Ito, Kenji*; Oka, Toshitaka*; Kobayashi, Yoshinori*; Shirai, Yasuharu*; Wada, Kenichiro*; Matsumoto, Masataka*; Fujinami, Masanori*; Hirade, Tetsuya; Honda, Yoshihide*; Hosomi, Hiroyuki*; et al.
no journal, ,
An interlaboratory comparison for positron annihilation lifetime measurements for pure nickel, polycarbonate (PC) and fused silica was performed. Based on the reported data of positron (for nickel) and positronium (for PC and fused silica) components, the uncertainties in the PAL measurements were estimated and their possible source was discussed.
Higuchi, Kensuke; Machida, Akihiko; Katayama, Yoshinori; Sakaki, Koji*; Nakamura, Yumiko*
no journal, ,
no abstracts in English
Higuchi, Kensuke; Machida, Akihiko; Katayama, Yoshinori; Sakaki, Koji*; Nakamura, Yumiko*
no journal, ,
no abstracts in English
