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Nakano, Satoshi*; Sano, Asami; Hattori, Takanori; Machida, Shinichi*; Komatsu, Kazuki*; Fujihisa, Hiroshi*; Yamawaki, Hiroshi*; Goto, Yoshito*; Kikegawa, Takumi*
Inorganic Chemistry, 60(5), p.3065 - 3073, 2021/03
Times Cited Count：10 Percentile：74.02(Chemistry, Inorganic & Nuclear)X-ray and neutron diffraction analyses of ammonia borane were conducted at ambient and high pressures. The H-H distance in dihydrogen bonds was shorter than twice the van der Waals radius (2.4 
). The half of the dihydrogen bonds were broken on phase transition from AP to the first high pressure phase (HP1) at approximately 1.2 GPa as revealed by an increase in the H-H distances. On further pressure increase, all of the H-H distances became shorter than 2.4 again, implying the pressure-induced reformation of the dihydrogen bonds. Furthermore, the HP1 transformed to the second one with the structure of 
(Z = 2) at about 11 GPa. In this phase transition, the inclination of the molecule axis became larger and the number of types of dihydrogen bonds increased from 6 to 11. Just before the third transition at 18.9 GPa, the shortest dihydrogen bond decreased to 1.65 . The present study experimentally first confirmed the breakage and reformation of the dihydrogen bonds by the structural change under pressure.
Matsuoka, Takahiro*; Fujihisa, Hiroshi*; Hirao, Naohisa*; Oishi, Yasuo*; Mitsui, Takaya; Masuda, Ryo; Seto, Makoto*; Yoda, Yoshitaka*; Shimizu, Katsuya*; Machida, Akihiko; et al.
Physical Review Letters, 107(2), p.025501_1 - 025501_4, 2011/07
Times Cited Count：28 Percentile：77.59(Physics, Multidisciplinary)Europium-hydride EuH
exposed to high-pressure H conditions has been found to exhibit structural and valence changes, 
(
=2, divalent) 
63/
(=2, 7.2-8.7 GPa) 
4/
(
2, 8.7-9.7 GPa) 4/
(2, 9.7 GPa-, trivalent). Having trivalent character and distorted cubic fcc structure, the 4/ structure is the 
-phase which has been commonly observed for other rare-earth metal hydrides. Our study clearly demonstrates that EuH is no longer an "irregular" member of the rare earth metal hydrides.
Matsuoka, Takehiro*; Shimizu, Katsuya*; Fujihisa, Hiroshi*; Hirao, Naohisa*; Oishi, Yasuo*; Yoda, Yoshitaka*; Mitsui, Takaya; Masuda, Ryo; Machida, Akihiko; Aoki, Katsutoshi; et al.
no journal, ,
Europium-hydride EuH exposed to high-pressure H conditions has been studied by X-ray diffraction and M
ssbauer spectroscopy measurements up to 50 GPa using synchrotron radiation. We report new structural and valence transitions, Pnma(x=2, divalent) P63/mmc(x=2, 7.2-8.7GPa) I4/m(x2, 8.7-9.7 GPa) I4/mmm(x2, 9.7 GPa, trivalent). The phase of I4/mmm having trivalent character is a small distortion from cubic fcc structure which has been commonly observed for -phase of all other trivalent rare-earth metal hydrides. Our study clearly demonstrates the first observation of -phase of EuH and suggest that the material is no longer an irregular member of the rare earth metal hydrides RH systems.
Honda, Mitsunori*; Machida, Akihiko; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Aoki, Katsutoshi; Arima, Hiroshi*; Komatsu, Kazuki*; Oshita, Hidetoshi*; et al.
no journal, ,
no abstracts in English
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; Hattori, Takanori; Honda, Mitsunori*; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Aoki, Katsutoshi; Komatsu, Kazuki*; Oshita, Hidetoshi*; Otomo, Toshiya*; et al.
no journal, ,
no abstracts in English
