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and TiH
up to 21 GPa by incoherent inelastic neutron scatteringHattori, Takanori; Nakamura, Mitsutaka; Iida, Kazuki*; Machida, Akihiko*; Sano, Asami; Machida, Shinichi*; Arima, Hiroshi*; Oshita, Hidetoshi*; Honda, Takashi*; Ikeda, Kazutaka*; et al.
Physical Review B, 106(13), p.134309_1 - 134309_9, 2022/10
Times Cited Count：0 Percentile：0(Materials Science, Multidisciplinary)Hydrogen vibration excitations of fluorite-type ZrH and TiH were investigated up to 21 GPa and 4 GPa, respectively, by incoherent inelastic neutron scattering experiments. The first excitation energies increased with pressure, as described by the equations 
(meV) = 141.4(2) + 1.02(2)
(GPa) and (meV) = 149.4(1) + 1.21(8)(GPa) for ZrH and TiH, respectively. Coupling with pressure dependence of lattice parameters, the relations between metal-hydrogen distance (
) and are found to be well described by the equations (meV) = 1.62(9)
10
(
(meV) = 1.47(21) 10 
(AA), respectively. The slopes of these curves are much steep compared to the previously reported trend in various fluorite-type metal hydrides at ambient pressure. The hydrogen wave function spreading showed that the local potential field for a hydrogen atom shrinks more intensively than the tetrahedral site. These behavior is likely caused by the rigid metal ion core and the resulting confinement of the hydrogen atom in the narrower potential field at high pressures.
Nakajima, Kenji; Kawakita, Yukinobu; Ito, Shinichi*; Abe, Jun*; Aizawa, Kazuya; Aoki, Hiroyuki; Endo, Hitoshi*; Fujita, Masaki*; Funakoshi, Kenichi*; Gong, W.*; et al.
Quantum Beam Science (Internet), 1(3), p.9_1 - 9_59, 2017/12
The neutron instruments suite, installed at the spallation neutron source of the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC), is reviewed. MLF has 23 neutron beam ports and 21 instruments are in operation for user programs or are under commissioning. A unique and challenging instrumental suite in MLF has been realized via combination of a high-performance neutron source, optimized for neutron scattering, and unique instruments using cutting-edge technologies. All instruments are/will serve in world-leading investigations in a broad range of fields, from fundamental physics to industrial applications. In this review, overviews, characteristic features, and typical applications of the individual instruments are mentioned.
Machida, Akihiko; Honda, Mitsunori*; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Aoki, Katsutoshi; Komatsu, Kazuki*; Arima, Hiroshi*; Oshita, Hidetoshi*; et al.
Physical Review Letters, 108(20), p.205501_1 - 205501_5, 2012/05
Times Cited Count：15 Percentile：65.67(Physics, Multidisciplinary)Hydrogen atoms absorbed in a metal occupy the interstitial sites of the metal lattice. In an fcc metal lattice, each metal atom has two tetrahedral (T) and one octahedral (O) sites that can accommodate hydrogen. Rare-earth metal La forms T-site occupied LaH
and fully occupied LaH
. O-site occupied or NaCl-type monohydride has yet to be reported for rare-earth metals. Previous X-ray diffraction measurements revealed the pressure-induced decomposition of an fcc-LaH
into H-rich and H-poor phases around 11 GPa. The present neutron diffraction measurements on LaD confirm the formation of NaCl-type LaD as a counterpart of the D-rich LaD
by disproportionation. First-principle calculations demonstrate that the NaCl-type LaH is stabilized at high pressures. Finding the NaCl-type LaH will pave the way for investigations on the site-dependent nature of hydrogen-metal interactions.
-Al(OH)
; Neutron diffraction measurements and ab initio calculationsMatsui, Masanori*; Komatsu, Kazuki*; Ikeda, Emi*; Sano, Asami; Goto, Hirotada*; Yagi, Takehiko*
American Mineralogist, 96(5-6), p.854 - 859, 2011/05
Times Cited Count：12 Percentile：37.48(Geochemistry & Geophysics)Neutron powder diffraction analyses of -Al(OD) revealed that the crystals are orthorhombic with space group 
2
22, but not 
as reported previously by X-ray diffraction data. The initial lattice parameters and the atomic positions of both Al and O were taken from previous X-ray structural analyses for the structure, while the H atom positions were determined using ab initio calculations. The -Al(OH) structure possesses one relatively long and two short O-H...O hydrogen bonds. Ab initio calculations are also used to find that -Al(OH) with space group 222 transforms to another high pressure polymorph with space group at around 67 GPa, and that the two short hydrogen bonds in -Al(OH) become both symmetric through the transformation, in which the protons are located at the midpoints of the O...O hydrogen bonds.
Ikeda, Kazuki*; Orimo, Shinichi*; Saito, Hiroyuki; Machida, Akihiko; Katayama, Yoshinori; Aoki, Katsutoshi
Suiso Seizo, Kyuzo, Chozo Zairyo To Anzenka, p.317 - 327, 2010/08
AlH is a metal hydride with a large gravimetric and volumetric hydrogen content (10.1 wt.% and 149kgH/m
, respectively), and therefore it is promising as a hydrogen storage material. The high capacity and low desorption temperature (80
150
C) have attracted much attention. In situ X-ray diffraction measurements for the Al-H binary system at high pressures and temperatures were performed to investigate the hydrogenation of aluminum metal immersed in hydrogen fluid as well as the phase stability of the aluminum hydride formed.
Hayashi, Takao; Tobita, Kenji; Nishio, Satoshi; Ikeda, Kazuki*; Nakamori, Yuko*; Orimo, Shinichi*; DEMO Plant Design Team
Fusion Engineering and Design, 81(8-14), p.1285 - 1290, 2006/02
Times Cited Count：20 Percentile：79.64(Nuclear Science & Technology)Neutron transport calculations were carried out to evaluate the capability of metal hydrides and borohydrides as an advanced shielding material. Some hydrides indicated considerably higher hydrogen content than polyethylene and solid hydrogen. The hydrogen-rich hydrides show superior neutron shielding capability to the conventional materials. From the temperature dependence of dissociation pressure, ZrH and TiH can be used without releasing hydrogen at the temperature of less than 640 C at 1 atm. ZrH and Mg(BH
) can reduce the thickness of the shield by 30% and 20% compared to a combination of steel and water, respectively. Mixing some hydrides with F82H produces considerable effects in 
-ray shielding. The neutron and -ray shielding capabilities decrease in order of ZrH 
Mg(BH) and F82H TiH and F82H water and F82H.
) observed by dispersive XAFSOyama, Takahiro; Matsumura, Daiju; Okajima, Yuka; Nishihata, Yasuo; Li, H.-W.*; Ikeda, Kazuki*; Orimo, Shinichi*; Takahashi, Isao*
no journal, ,
Complex bronhydride Mg(B) is known to have lower dehydrogenation temperature by doping Ti chloride or Ti oxide. In this study, we observed real-time local structural transformation around Ti atoms during temperature induced dehydrogenation by dispersive XAFS method. For the case of Ti chloride doping, it is revealed that Ti atoms form bronhydride complex before temperature heating. Adrupt hydrogen desorption from Ti bronhydride makes the dehydrogenation temperature small. On the other hand, in the case of Ti oxide doping, Ti keeps its structure before heating. As temperature is raised, Ti slowly changes to TiB with catalytic behavior for dehydrogenation of Mg(BH).
on the hydrogen storage property of Mg(BH)Matsumura, Daiju; Oyama, Takahiro*; Okajima, Yuka; Nishihata, Yasuo; Li, H.-W.*; Ikeda, Kazuki*; Orimo, Shinichi*
no journal, ,
Mg(BH) shows 14.9% mass density of hydrogen and has attracted much attention in many years. Recently, it was reported that the hydrogen desorption temperature decreases from 530 K to 360 K by TiCl doping. In this study, we applied the X-ray absorption fine structure spectra to the static and dynamic observations in order to understand the local structure around doped Ti atoms. It has been revealed that the hydrogen desorption around 420 K is induced by the resolution of Ti(BH) generated from the reaction of TiCl and Mg(BH). Another hydrogen desorption reaction over 470 K was considered to be induced by the catalytic reaction of TiB.
Machida, Akihiko; Hattori, Takanori; Honda, Mitsunori*; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Aoki, Katsutoshi; Komatsu, Kazuki*; Arima, Hiroshi*; Oshita, Hidetoshi*; et al.
no journal, ,
We have investigated the structural properties of rare-earth metal hydrides under high pressure. LaH has the CaF type structure in which the H atoms locate at the tetrahedral interstitial sites (T-sites) of the fcc metal lattice. Synchrotron radiation X-ray diffraction and infrared reflection experiments revealed disproportionation reaction of LaH into the H-poor and H-rich phases around 11 GPa. Before the disproportionation reaction, we have found that the fcc metal lattice transformed into tetragonal lattice. The ordering of the H atoms in the octahedral-sites (O-sites) causes the tetragonal distortion of LaH. The tetragonal transformation and successive disproportionation reaction of LaH would closely relate to the inter-site transfer of the H atoms between the T- and O-sites. We have performed the neutron diffraction experiments of LaD to investigate the change of the positions and occupancies of the hydrogen atoms under high pressure.
Machida, Akihiko; Honda, Mitsunori*; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Aoki, Katsutoshi; Komatsu, Kazuki*; Arima, Hiroshi*; Oshita, Hidetoshi*; et al.
no journal, ,
Hydrogen atoms absorbed in a metal occupy the interstitial sites of the metal lattice. In an fcc metal lattice, each metal atom has two tetrahedral (T) and one octahedral (O) sites that can accommodate hydrogen. Rare-earth metal La forms T-site occupied LaH and fully occupied LaH. Previous X-ray diffraction measurements revealed the pressure-induced decomposition of an fcc-LaH into H-rich and H-poor phases around 11 GPa. We performed the neutron diffraction measurements on LaD, and found the formation of NaCl-type LaD as a phase separation products. We have first found the NaCl-type rare-earth metal monohydride.
Hirouchi, Daisuke*; Matsuta, Nobuhisa*; Ishiyama, Tatsuya*; Sugito, Nobuhiko*; Takeshita, Yoshihiro*; Mizutani, Kotaro*; Yasue, Kenichi*; Fujita, Natsuko; Sawa, Sho*; Doke, Ryosuke*; et al.
no journal, ,
no abstracts in English
Mizutani, Kotaro*; Hirouchi, Daisuke*; Matsuta, Nobuhisa*; Ishiyama, Tatsuya*; Sugito, Nobuhiko*; Yasue, Kenichi*; Takeshita, Yoshihiro*; Fujita, Natsuko; Sawa, Sho*; Doke, Ryosuke*; et al.
no journal, ,
no abstracts in English
Hattori, Takanori; Nakamura, Mitsutaka; Iida, Kazuki*; Machida, Akihiko*; Sano, Asami; Machida, Shinichi*; Arima, Hiroshi*; Oshita, Hidetoshi*; Honda, Takashi*; Ikeda, Kazutaka*; et al.
no journal, ,
Recently, the high-pressure state of metal hydrides has attracted much attention due to the discovery of superhydrides with high-
near room temperature under ultra-high pressure. The vibrational state of hydrogen is important to understand the origin of high and to search for materials with higher . Incoherent Inelastic Neutron Scattering (IINS) is a powerful tool to study the vibrational excitations of hydrogen. Therefore, vibrational excitations of various metal hydrides have been investigated, but a unified understanding is still lacking due to the differences in the lattice size and electronic states. Pressure allows us to investigate the nature of the lattice more rationally because the lattice size can be changed continuously. In the present work, we have developed an apparatus for IINS under high pressure, and succeeded in observing vibrational excitations of hydrogen in ZrH and TiH up to 21 GPa. In this talk, we will introduce the principle of IINS, the experiments, and the results obtained.
