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Machida, Akihiko*; Saito, Hiroyuki*; Aoki, Katsutoshi*; Komatsu, Kazuki*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; Machida, Shinichi*; Sato, Toyoto*; Orimo, Shinichi*
Physical Review B, 111(22), p.224413_1 - 224413_6, 2025/06
The crystal and magnetic structures of antiferromagnetic Mn deuterides formed by hydrogenating Mn metal at high temperature and high pressure, fcc -MnDx and hcp
-MnDx, were investigated by in-situ neutron powder diffraction. Deuterium atoms partially occupied the octahedral interstitial positions of the fcc and hcp metal lattices. The site occupancies increased rapidly with decreasing temperature from
700 to
450 K and remained down to 300 K. N
el temperature of 543(10) K was determined for
-MnD
. For
-MnD
, saturation magnetic moment and N
el temperature were determined to be 0.82(1)
and 347(3) K, respectively. The N
el temperatures determined for
-MnD
and
-MnD
are consistent with those predicted by the respective Slater-Pauling curves proposed in previous studies. The updated N
el temperatures provide insights into the development of more accurate Slater-Pauling curves based on electronic band structure calculations.
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), 15, p.8861_1 - 8861_2, 2024/10
Times Cited Count:0 Percentile:0.00(Multidisciplinary Sciences)In our previous article (Nature Commun. 5, 5063 (2014)), the site occupancies of D atoms dissolved in an fcc Fe metal lattice were investigated via Rietveld refinement of neutron powder diffraction patterns collected at 988 K and 6.3 GPa. The fcc metal lattice has two interstitial sites available for accommodating D atoms: octahedral and tetrahedral sites. The Rietveld refinement revealed that D atoms occupied mainly the octahedral sites with occupancy of 0.532 and slightly the tetrahedral sites with occupancy of 0.056. Subsequent density-functional-theory (DFT) calculations by Antonov (Phys. Rev. Mater. 2019)) showed that the occupation energy on the tetrahedral site was significantly higher than that on the octahedral site; the tetrahedral site occupation was unlikely to occur even at temperatures as high as 988 K. We reexamined the site occupancies of D-atom by Rietveld refinement including extinction correction. As a result, the octahedral occupancy was increased to 0.60 and the tetrahedral occupancy was reduced to zero. The occupation of only the octahedral site for D atom is consistent with the DFT calculation, although in contrast to the previous results.
Mori, Yuichiro*; Kagi, Hiroyuki*; Aoki, Katsutoshi*; Takano, Masahiro*; Kakizawa, Sho*; Sano, Asami; Funakoshi, Kenichi*
Earth and Planetary Science Letters, 634, p.118673_1 - 118673_8, 2024/05
Times Cited Count:1 Percentile:47.42(Geochemistry & Geophysics)To investigate silicon effects on the hydrogen-induced volume expansion of iron, neutron diffraction and X-ray diffraction experiments were conducted to examine hcp-FeSi
under high pressures and high temperatures. Neutron diffraction experiments were performed on the deuterated hcp-Fe
Si
at 13.5 GPa and 900 K, and at 12.1 GPa and 300 K. By combining the P-V-T equation of state of hcp-Fe
Si
, present results indicate that the hydrogen-induced volume expansion of hcp-Fe
Si
is 10% greater than that of pure hcp iron. Using the obtained values, we estimated the hydrogen content that would reproduce the density deficit in the inner core, which was 50% less than that without the effect of silicon. Possible hydrogen content,
, in the inner core and the outer core was calculated to be 0.07 and 0.12-0.15, respectively, when reproducing the density deficit of the inner core with hcp-Fe
Si
Hx.
Takano, Masahiro*; Kagi, Hiroyuki*; Mori, Yuichiro*; Aoki, Katsutoshi*; Kakizawa, Sho*; Sano, Asami; Iizuka-Oku, Riko*; Tsuchiya, Taku*
Journal of Mineralogical and Petrological Sciences (Internet), 119(1), p.240122_1 - 240122_9, 2024/00
Times Cited Count:0 Percentile:0.00(Mineralogy)Hydrogenation of iron sulfide (FeS) under high-pressure and high-temperature conditions has attracted attention because hydrogen and sulfur are promising candidates as light elements in the cores of the Earth and other terrestrial planets. In earlier reports describing the hydrogenation of FeS, the chemical compositions of starting materials were not fully clarified. This study reports in-situ neutron and X-ray diffraction measurements under high-pressure and high-temperature conditions of an Fe-S-H system using a stochiometric Fe1.000S (troilite) as a starting material. The occupancies determined were significantly lower than those reported from earlier studies, indicating that the hydrogenation of FeS can be affected strongly by the stoichiometry of iron sulfide.
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:5 Percentile:71.52(Geochemistry & Geophysics)The phase relation and crystal structure of FeNi
H
(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) Fe
Ni
D
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:2 Percentile:10.84(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-Fe
Si
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 (Fe
Si
) 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:5 Percentile:25.28(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:5 Percentile:19.41(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:31 Percentile:83.40(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:36 Percentile:69.33(Chemistry, Multidisciplinary)Saito, Hiroyuki; Machida, Akihiko; Matsuoka, Takehiro*; Aoki, Katsutoshi*
Solid State Communications, 205, p.24 - 27, 2015/03
Times Cited Count:9 Percentile:36.54(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:19 Percentile:59.63(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:66 Percentile:87.34(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:25 Percentile:68.14(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:4 Percentile:75.11(Physics, Applied)We 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:15 Percentile:52.02(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:36.31(Physics, Applied)