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Ekawa, Hiroyuki; Ashikaga, Sakiko; Hasegawa, Shoichi; Hashimoto, Tadashi; Hayakawa, Shuhei; Hosomi, Kenji; Ichikawa, Yudai; Imai, Kenichi; Kimbara, Shinji*; Nanamura, Takuya; et al.
Progress of Theoretical and Experimental Physics (Internet), 2019(2), p.021D02_1 - 021D02_11, 2019/02
Times Cited Count：25 Percentile：83.76(Physics, Multidisciplinary)
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：17 Percentile：67.41(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.
Nakamura, Atsuko*; Ichikawa, Kazuki*; Kojima, Kazuaki*; Ono, Yutaka; Kobayashi, Yasuhiko; Tanaka, Shigeo*; Sakata, Yoichi*
no journal, ,
Phytochelatin (PC) has been shown to play an important role in heavy metal detoxification. However, Arabidopsis transgenic plants overexpressing the PC synthase gene failed to show an increase in Cd tolerance. To explore a novel heavy metal detoxification mechanism, we screened for an Arabidopsis Cd-sensitive mutant (
) by carbon ion beam mutagenesis, which causes large base pair deletions at random loci in the genome. Genetic analyses and GSH synthesis inhibitor studies revealed that the phenotype was different from those of PC synthesis mutants. Moreover, Cd content in shoots of cultured on Cd-containing media was similar to wild type, suggesting that Cd-sensitive phenotype of was not attributed to the Cd transport system from roots to shoots. In the rough mapping, was localized to approximately 300kbp region of chromosome 4. One of the genes was found to have a 2.5 kbp deletion in the promoter region.
Aoki, Katsutoshi; Machida, Akihiko; Honda, Mitsunori; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Komatsu, Kazuki*; Arima, Hiroshi; Otomo, Toshiya*; et al.
no journal, ,
Neutron diffraction measurements have revealed that LaD undergoes phase separation at high pressure with the relocation of deuterium atoms in the interstitial sites of La metal lattice. Deuterium atoms, which occupy the tetrahedral sites of the fcc metal lattice in LaD, move into the empty octahedral sites at 11 GPa to form LaD and LaD
both having fcc metal lattices. Mono-hydride with an NaCl structure, which is common for mono-hydrides of transition metals, is formed in rare-earth metals for the first time. The first-principle calculations showed that LaH is stable at low pressure and it undergoes a phase separation into LaH and LaH at 10 GPa, which is excellent agreement with the experimental results. Enthalpy comparison shows that unusual volume contraction in LaH than LaH explains the phase separation phenomena. Lattice dynamics calculations on these lanthanum hydrides shed light on the detailed mechanism.
Aoki, Katsutoshi; Machida, Akihiko; Honda, Mitsunori; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Komatsu, Kazuki*; Arima, Hiroshi; Otomo, Toshiya*; et al.
no journal, ,
Synchrotron X-ray and neutron diffraction measurements have revealed that LaD undergoes phase separation at high pressure with the relocation of deuterium atoms in the interstitial sites of La metal lattice. Synchrotron X-ray and neutron experiments were made at BL22XU, SPring-8 and a total scattering device, NOVA, J-PARC. Deuterium atoms, which occupy the tetrahedral sites of the fcc metal lattice in LaD, move into the empty octahedral sites at 11 GPa to form LaD and LaD both having fcc metal lattices. Mono-hydride with an NaCl structure, which is common for mono-hydrides of transition metals, is formed in rare-earth metals for the first time. The first-principle calculations showed that LaH is stable at low pressure and it undergoes a phase separation into LaH and LaH at 10 GPa, which is excellent agreement with the experimental results.
Machida, Akihiko; Honda, Mitsunori; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Aoki, Katsutoshi; Komatsu, Kazuki*; Arima, Hiroshi; Oshita, Hidetoshi*; et al.
no journal, ,
Formation of an NaCl-type mono-deuteride LaD has been found by neutron diffraction experiments at high pressure. The NaCl-type structure has been reported for alkaline hydrides and transition metal hydrides, but not for rare-earth metal hydrides. The NaCl-type mono-hydride is formed in rare-earth metals for the first time. Lanthanum mono-deuteride is formed as a result of the phase separation of the di-deuteride under high pressure. This result suggests that the three different hydrides, mono-, di-, and tri-hydrides, with the fcc metal lattice are realized. The hydrogen atoms occupy only O-sites, only T-sites and both O-sites and T-sites in the mono-, di-, and tri-hydrides, respectively. Hence, it is expected that the H-M bonding nature is different for each hydride.
Machida, Akihiko; Honda, Mitsunori; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Aoki, Katsutoshi; Komatsu, Kazuki*; Arima, Hiroshi; Oshita, Hidetoshi*; et al.
no journal, ,
We have investigated the pressure-induced phase separation in rare-earth metal dihydrides by synchrotron radiation X-ray diffraction and neutron diffraction experiments. Rare-earth metal hydrides exhibit the stoichiometoric dihydride and trihydride. The dihydride is a metallic while trihydride is an insulator. Recently, we have found the pressure induced phase separation in the lanthanum dihydride. This phenomenon is understood as the decomposition into the hydrogen-poor and rich phases under high pressure. However, the hydrogen occupancy and position have been unclear yet. Our neutron diffraction experiments have revealed that an NaCl-type mono-deuteride is formed as a counterpart of the deuterium-rich phase.
Aoki, Katsutoshi; Machida, Akihiko; Honda, Mitsunori; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Komatsu, Kazuki*; Arima, Hiroshi; Otomo, Toshiya*; et al.
no journal, ,
Rare-earth metal La forms T-site occupied fcc-LaH and fully occupied fcc-LaH, the former is metallic and the latter is insulating. Our previous synchrotron X-ray and infrared measurements revealed that the dihydride decomposed into hydrogen-rich and hydrogen-poor phases upon compression to 11 GPa at ambient temperature; the hydrogen rich phase was identified as LaH but the hydrogen composition and occupation sites of the hydrogen-poor phase remained undetermined. The crystal structure of the hydrogen-poor phase was investigated for LaD by neutron diffraction measurement with a total diffractometer NOVA at J-PARC. The formation of NaCl-type LaD as a counterpart of LaD by the decomposition was confirmed from the diffraction profiles. First-principle enthalpy and lattice dynamic calculations have demonstrated that the NaCl-type LaH is stabilized at high pressures.
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.
