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Shito, Chikara*; Kagi, Hiroyuki*; Kakizawa, Sho*; Aoki, Katsutoshi*; Komatsu, Kazuki*; Iizuka, Riko*; Abe, Jun*; Saito, Hiroyuki*; Sano, Asami; Hattori, Takanori
American Mineralogist, 108(4), p.659 - 666, 2023/04
Times Cited Count:0 Percentile:68.97(Geochemistry & Geophysics)The phase relation and crystal structure of FeNiH (D) at high pressures and temperatures up to 12 GPa and 1000 K were clarified by in-situ X-ray and neutron diffraction measurements. Under conditions of the present study, no deuterium atoms occupied tetragonal () sites of face-centered cubic (fcc) FeNiD unlike fcc FeH(D). The deuterium-induced volume expansion per deuterium was determined as 2.45(4) and 3.31(6) for fcc and hcp phases, respectively, which were significantly larger than the corresponding values for FeD. The value slightly increased with increasing temperature. This study suggests that only 10% of nickel in iron drastically changes the behaviors of hydrogen in metal. Assuming that is constant regardless of pressure, the maximum hydrogen content in the Earth's inner core is estimated to be one to two times the amount of hydrogen in the oceans.
Mori, Yuichiro*; Kagi, Hiroyuki*; Kakizawa, Sho*; Komatsu, Kazuki*; Shito, Chikara*; Iizuka, Riko*; Aoki, Katsutoshi*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; et al.
Journal of Mineralogical and Petrological Sciences, 116(6), p.309 - 313, 2021/00
Times Cited Count:0 Percentile:0.02(Mineralogy)The Earth's core is believed to contain some light elements because it is 10% less dense than pure Fe under the corresponding pressure and temperature conditions. Hydrogen, a promising candidate among light elements, has phase relations and physical properties that have been investigated mainly for the Fe-H system. This study specifically examined an Fe-Si-H system using in-situ neutron diffraction experiments to investigate the site occupancy of deuterium of hcp-FezSi hydride at 14.7 GPa and 800 K. Results of Rietveld refinement indicate hcp-FeSi hydride as having deuterium (D) occupancy of 0.24(2) exclusively at the interstitial octahedral site in the hcp lattice. The effect on the site occupancy of D by addition of 2.6 wt% Si into Fe (FeSi) was negligible compared to results obtained from an earlier study of an Fe-D system (Machida et al., 2019).
Saito, Hiroyuki*; Machida, Akihiko*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; Sato, Toyoto*; Orimo, Shinichi*; Aoki, Katsutoshi*
Physica B; Condensed Matter, 587, p.412153_1 - 412153_6, 2020/06
Times Cited Count:2 Percentile:13.29(Physics, Condensed Matter)The site occupancy of deuterium (D) atoms in face-centered-cubic nickel (fcc Ni) was measured along a cooling path from 1073 to 300 K at an initial pressure of 3.36 GPa via in situ neutron powder diffraction. Deuterium atoms predominantly occupy the octahedral (O) sites and slightly occupy the tetrahedral (T) sites of the fcc metal lattice. The O-site occupancy increases from 0.4 to 0.85 as the temperature is lowered from 1073 to 300 K. Meanwhile, the T-site occupancy remains c.a. 0.02. The temperature-independent behavior of the T-site occupancy is unusual, and its process is not yet understood. From the linear relation between the expanded lattice volume and D content, a D-induced volume expansion of 2.09(13) atom was obtained. This value is in agreement with the values of 2.14-2.2 atom previously reported for Ni and Ni Fe alloy.
Saito, Hiroyuki*; Machida, Akihiko*; Iizuka, Riko*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; Sato, Toyoto*; Orimo, Shinichi*; Aoki, Katsutoshi*
Scientific Reports (Internet), 10, p.9934_1 - 9934_8, 2020/06
Times Cited Count:3 Percentile:15.49(Multidisciplinary Sciences)Neutron powder diffraction profiles were collected for iron deuteride (FeDx) while the temperature decreased from 1023 to 300 K for a pressure range of 4-6 GPa. The ' deuteride with a double hexagonal close-packed (dhcp) structure, which coexisted with other stable or metastable deutrides at each temperature and pressure condition, formed solid solutions with a composition of FeD at 673 K and 6.1 GPa and FeD at 603 K and 4.8 GPa. Upon stepwise cooling to 300 K, the D-content x increased to a stoichiometric value of 1.0 to form monodeuteride FeD. In the dhcp FeD at 300 K and 4.2 GPa, dissolved D atoms fully occupied the octahedral interstitial sites, slightly displaced from the octahedral centers in the dhcp metal lattice, and the dhcp sequence of close-packed Fe planes contained hcp-stacking faults at 12%. Magnetic moments with 2.11 0.06 B/Fe-atom aligned ferromagnetically in parallel on the Fe planes.
Machida, Akihiko*; Saito, Hiroyuki*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; Sato, Toyoto*; Orimo, Shinichi*; Aoki, Katsutoshi*
Scientific Reports (Internet), 9(1), p.12290_1 - 12290_9, 2019/08
Times Cited Count:21 Percentile:83.48(Multidisciplinary Sciences)Hexagonal close-packed iron hydride, hcp FeHx, is absent from the conventional phase diagram of the Fe-H system, although hcp metallic Fe exists stably over extensive temperature () and pressure () conditions, including those corresponding to the Earth's inner core. X-ray and neutron diffraction measurements at temperatures ranging from 298 to 1073 K and H pressures ranging from 4 to 7 GPa revealed that the hcp hydride was formed for FeH compositions when . Hydrogen atoms occupied the octahedral interstitial sites of the host metal lattice both partially and randomly. The hcp hydride exhibited a H-induced volume expansion of 2.48(5) /H-atom, which was larger than that of the face-centered cubic (fcc) hydride. The hcp hydride showed an increase in with , whereas the fcc hydride showed a corresponding decrease. The present study provides guidance for further investigations of the Fe-H system over an extensive -- region.
Takagi, Shigeyuki*; Iijima, Yuki*; Sato, Toyoto*; Saito, Hiroyuki; Ikeda, Kazutaka*; Otomo, Toshiya*; Miwa, Kazutoshi*; Ikeshoji, Tamio*; Aoki, Katsutoshi*; Orimo, Shinichi*
Angewandte Chemie; International Edition, 54(19), p.5650 - 5653, 2015/05
Times Cited Count:30 Percentile:67.58(Chemistry, Multidisciplinary)Saito, Hiroyuki; Machida, Akihiko; Matsuoka, Takehiro*; Aoki, Katsutoshi*
Solid State Communications, 205, p.24 - 27, 2015/03
Times Cited Count:8 Percentile:39.05(Physics, Condensed Matter)Aoki, Katsutoshi*; Machida, Akihiko; Saito, Hiroyuki; Hattori, Takanori; Sano, Asami
Hamon, 25(1), p.26 - 31, 2015/02
The deuterization process of fcc Fe to form solid-solution fcc FeD was investigated by in situ neutron diffraction measurements at high temperature and high pressure. In a completely deuterized specimen at 988 K and 6.3 GPa, deuterium atoms occupy the octahedral and tetrahedral interstitial sites with an occupancy of 0.532(9) and 0.056(5), respectively, giving a deuterium composition of 0.64(1). During deuterization, the metal-lattice expands approximately linearly with deuterium composition at a rate of 2.21 per deuterium atom. The minor occupation of tetrahedral site is likely driven by the intersite movement of deuterium atoms along the direction in the fcc metal lattice. These results provide implications for the light elements in the Earth's core and the mechanism of hydrogen embrittlement of ferrous metals.
Aoki, Katsutoshi*; Machida, Akihiko*; Saito, Hiroyuki*; Hattori, Takanori; Sano, Asami
Hamon, 25(1), p.26 - 31, 2015/02
The deuterization process of fcc Fe to form solid1solution fcc FeD was investigated by neutron diffraction measurements at high temperature and high pressure. In a completely deuterized specimen at 988 K and 6.3 GPa, deuterium atoms occupy the octahedral and tetrahedral interstitial sites with an occupancy of 0.532(9) and 0.056(5), respectively, giving a deuterium composition of 0.64(1). During deuterization, the metal-lattice expands approximately linearly with deuterium composition at a rate of 2.21 per deuterium atom. The minor occupation of tetrahedral site is likely driven by the intersite movement of deuterium atoms along the 111 direction in the fcc metal lattice. These results provide implications for the light elements in the Earth's core and the mechanism of hydrogen embrittlement of ferrous metals.
Saito, Hiroyuki; Machida, Akihiko; Aoki, Katsutoshi
Chinese Science Bulletin, 59(36), p.5290 - 5301, 2014/12
Times Cited Count:14 Percentile:54.61(Multidisciplinary Sciences)Machida, Akihiko; Saito, Hiroyuki; Sugimoto, Hidehiko*; Hattori, Takanori; Sano, Asami; Endo, Naruki*; Katayama, Yoshinori; Iizuka, Riko*; Sato, Toyoto*; Matsuo, Motoaki*; et al.
Nature Communications (Internet), 5, p.5063_1 - 5063_6, 2014/09
Times Cited Count:47 Percentile:86.18(Multidisciplinary Sciences)Iron hydride FeH, is thermodynamically stable only at high hydrogen pressure of several GPa. To investigate the hydrogenation process and hydrogen state in iron hydride, it is necessary to carry out the in-situ measurement under high pressure and high temperature. In this study, we performed the in-situ neutron diffraction measurement of Fe-D system using the high pressure neutron diffractometer PLANET in the MLF, J-PARC, and determined the deuterium occupying sites and occupancies in fcc-FeD. We found the minor occupation of tetrahedral sites under high pressure and high temperature. We considered the mechanism of the minor occupation based on the Quantum-mechanical calculation.
Saito, Hiroyuki; Takagi, Shigeyuki*; Matsuo, Motoaki*; Iijima, Yuki*; Endo, Naruki*; Aoki, Katsutoshi*; Orimo, Shinichi*
APL Materials (Internet), 2(7), p.076103_1 - 076103_7, 2014/07
Times Cited Count:23 Percentile:70.61(Nanoscience & Nanotechnology)Machida, Akihiko; Watanuki, Tetsu; Kawana, Daichi*; Aoki, Katsutoshi
Journal of Physics; Conference Series, 500(2), p.022001_1 - 022001_5, 2014/05
Times Cited Count:2 Percentile:51.17We found that LaH decomposed into two different molar-volume phases at 11 GPa at room temperature through synchrotron radiation X-ray diffraction (SR-XRD) measurements. Observed decomposition suggests that the H-poor and H-rich phases are spontaneously formed by pressurization, namely, a pressure-induced disproportionation reaction. Observed disproportionation reaction accompanies the transfer of the H atoms between the interstitial sites. Diffusivity of the H atoms suppresses as the temperature decreases. Hence we have investigated this disproportionation of LaH in the low H diffusivity case at low temperature.SR-XRD measurements at high pressure and low temperature were carried out at BL22XU, SPring-8. We found the disproportionation at 13.5 GPa even at 200 K. The volume fraction of the H-poor phase at 200 K is larger than that at room temperature. The disproportionation at low temperature will be discussed on the basis of the X-ray diffraction data.
Saito, Hiroyuki; Takagi, Shigeyuki*; Aoki, Katsutoshi; Orimo, Shinichi*
Hoshako, 27(1), p.10 - 19, 2014/01
no abstracts in English
Saito, Hiroyuki; Takagi, Shigeyuki*; Endo, Naruki; Machida, Akihiko; Aoki, Katsutoshi; Orimo, Shinichi*; Katayama, Yoshinori
APL Materials (Internet), 1(3), p.032113_1 - 032113_7, 2013/09
Times Cited Count:14 Percentile:54.18(Nanoscience & Nanotechnology)Takagi, Shigeyuki*; Ikeshoji, Tamio*; Matsuo, Motoaki*; Sato, Toyoto*; Saito, Hiroyuki; Aoki, Katsutoshi; Orimo, Shinichi*
Applied Physics Letters, 103(11), p.113903_1 - 113903_4, 2013/09
Times Cited Count:9 Percentile:38.1(Physics, Applied)Machida, Akihiko; Honda, Mitsunori*; Hattori, Takanori; Sano, Asami; Watanuki, Tetsu; Katayama, Yoshinori; Aoki, Katsutoshi; Oshita, Hidetoshi*; Ikeda, Kazutaka*; Otomo, Toshiya*
Hamon, 23(2), p.131 - 136, 2013/05
Recently, we have revealed formation of NaCl-type LaD using synchrotron radiation X-ray diffraction and neutron diffraction measurements under high pressure. Previously, we have found that LaH decomposes into two phases, which have different hydrogen compositions, the H-poor and H-rich phases, at 11 GPa at room temperature by synchrotron radiation X-ray diffraction. Recent neutron diffraction measurements on LaD confirmed the formation of a NaCl-type LaD as the D-poor phase. This is the first observation of a formation of the rare-earth metal monodeuteride. Present result indicates that that rare-earth metal can form a series of stoichiometric hydrides, such as mono-, di-, and trihydride with the fcc metal lattice.
Sato, Ryutaro*; Saito, Hiroyuki; Endo, Naruki; Takagi, Shigeyuki*; Matsuo, Motoaki*; Aoki, Katsutoshi; Orimo, Shinichi*
Applied Physics Letters, 102(9), p.091901_1 - 091901_4, 2013/03
Times Cited Count:23 Percentile:73.58(Physics, Applied)Takagi, Shigeyuki*; Saito, Hiroyuki; Endo, Naruki; Sato, Ryutaro*; Ikeshoji, Tamio*; Matsuo, Motoaki*; Miwa, Kazutoshi*; Aoki, Katsutoshi; Orimo, Shinichi*
Physical Review B, 87(12), p.125134_1 - 125134_6, 2013/03
Times Cited Count:12 Percentile:53.67(Materials Science, Multidisciplinary)Endo, Naruki; Saito, Hiroyuki; Machida, Akihiko; Katayama, Yoshinori; Aoki, Katsutoshi
Journal of Alloys and Compounds, 546, p.270 - 274, 2013/01
Times Cited Count:6 Percentile:35.86(Chemistry, Physical)