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solution in the gigapascal pressure rangeYamaguchi, Toshio*; Fukuyama, Nami*; Yoshida, Koji*; Katayama, Yoshinori*; Machida, Shinichi*; Hattori, Takanori
Liquids, 3(3), p.288 - 302, 2023/09
We report the structure of an aqueous 2 mol/kg MgCl solution at pressures from 0.1 MPa to 4 GPa and temperatures from 300 to 500 K revealed by X-ray and neutron scattering measurements. The scattering data are analyzed by empirical potential structure refinement (EPSR) modeling to derive the pair distribution functions, coordination number distributions, angle distributions, and spatial density functions as a function of pressure and temperature. Mg
forms rigid solvation shells extended to the third shell; the first solvation shell of six-fold octahedral coordination with about six water molecules at 0 GPa transforms into about five water molecules and one Cl
due to the formation of the contact ion pairs in the GPa pressure range. The Cl solvation shows a substantial pressure dependence; the coordination number of a water oxygen atom around Cl increases from 8 at 0.1 MPa/300 K to 10 at 4 GPa/500 K. The solvent water transforms the tetrahedral network structure at 0.1 MPa/300 K to a densely packed structure in the GPa pressure range; the number of water oxygen atoms around a central water molecule gradually increases from 4.6 at 0.1 MPa/298 K to 8.4 at 4 GPa/500 K.
Yamaguchi, Toshio*; Yoshida, Koji*; Machida, Shinichi*; Hattori, Takanori
Journal of Molecular Liquids, 365, p.120181_1 - 120181_10, 2022/11
Times Cited Count：0 Percentile：0.01(Chemistry, Physical)Neutron scattering measurements were performed on an aqueous 3 mol/kg NaCl solution in DO at temperature and pressure conditions of 0.1 MPa/298K, 1 GPa/298K, 1 GPa/523K, and 4 GPa/523K. The empirical potential structure refinement method was applied to the obtained data to extract the pair correlation function, coordination number distribution, angular distribution (orientation correlation), and spatial density function (3-D structure). From those results, pressure and temperature dependence of solvation and association of ions and solvent-water structure were discussed.
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.
Yamashita, Keishiro*; Komatsu, Kazuki*; Klotz, S.*; Fabelo, O.*; Fern
ndez-D
az, M. T.*; Abe, Jun*; Machida, Shinichi*; Hattori, Takanori; Irifune, Tetsuo*; Shimmei, Toru*; et al.
Proceedings of the National Academy of Sciences of the United States of America, 119(40), p.e2208717119_1 - e2208717119_6, 2022/10
Times Cited Count：1 Percentile：0(Multidisciplinary Sciences)Here we present the first elucidation of the disordered structure of ice VII, the dominant high-pressure form of water, at 2.2 GPa and 298 K from both single-crystal and powder neutron diffraction techniques. We reveal the three-dimensional atomic distributions from the maximum entropy method and unexpectedly find a ring-like distribution of hydrogen in contrast to the commonly-accepted discrete sites. In addition, total scattering analysis at 274 K clarified the difference in the intermolecular structure from ice VIII, the ordered counterpart of ice VII, despite an identical molecular geometry. Our complementary structure analyses robustly demonstrate the unique disordered structure of ice VII. Furthermore, these noble findings are related to the proton dynamics which drastically vary with pressure, and will contribute to an understanding of the structural origin of anomalous physical properties of ice VII under pressures.
Zhang, W. Q.*; Yamaguchi, Toshio*; Fang, C. H.*; Yoshida, Koji*; Zhou, Y. Q.*; Zhu, F. Y.*; Machida, Shinichi*; Hattori, Takanori; Li, W.*
Journal of Molecular Liquids, 348, p.118080_1 - 118080_11, 2022/02
Times Cited Count：1 Percentile：33.21(Chemistry, Physical)The ion hydration and association and hydrogen-bonded water structure in an aqueous 3 mol/kg RbCl solution were investigated at 298 K/0.1 MPa, 298 K/1 GPa, 523 K/1 GPa, and 523 K/4 GPa by neutron diffraction combined with EPSR methods. The second hydration layer of Rb
and Cl becomes evident under elevated pressure and temperature conditions. The average oxygen coordination number of Rb (Cl) in the first hydration layer increases from 6.3 (5.9) ambient pressure to 8.9 (9.1) at 4 GPa, while decreasing coordination distance from 0.290 nm (0.322 nm) to 0.288 nm (0.314 nm). The orientation of the water dipole in the first solvation shell of Rb and a central water molecule is sensitive to pressure, but that in the first solvation shell of Cl does not change very much. The number of contact-ion pairs Rb-Cl decreases with elevated temperature and increases with elevated pressure. Water molecules are closely packed, and the tetrahedral hydrogen-bonded network of water molecules no longer exists in extreme conditions.
Sano, Asami; Kakizawa, Sho*; Shito, Chikara*; Hattori, Takanori; Machida, Shinichi*; Abe, Jun*; Funakoshi, Kenichi*; Kagi, Hiroyuki*
High Pressure Research, 41(1), p.65 - 74, 2021/03
Times Cited Count：2 Percentile：36.98(Physics, Multidisciplinary)We applied Kawai-type multi-anvil assemblies (MA6-8) for time-of-flight neutron-diffraction experiments to achieve high pressures and high temperatures simultaneously. To achieve sufficient signal intensities, the angular access to the sample was enlarged using slits and tapers on the first-stage anvils. Using SiC-binder sintered diamond for the second-stage anvils that transmits neutrons, sufficient signal intensities were achieved at a high-pressure of 
23.1 GPa. A high-temperature experiment was also conducted at 16.2 GPa and 973 K, validating the use of tungsten carbide for the second-stage anvils. The present study reveals the capability of the MA6-8 cells in neutron-diffraction experiments to attain pressures and temperatures beyond the limits of the conventional MA6-6 cells used in the high-pressure neutron diffractometer PLANET at the MLF, J-PARC.
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：8 Percentile：74.78(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.
Miao, P.*; Tan, Z.*; Lee, S. H.*; Ishikawa, Yoshihisa*; Torii, Shuki*; Yonemura, Masao*; Koda, Akihiro*; Komatsu, Kazuki*; Machida, Shinichi*; Sano, Asami; et al.
Physical Review B, 103(9), p.094302_1 - 094302_18, 2021/03
Times Cited Count：1 Percentile：0(Materials Science, Multidisciplinary)The layered perovskite PrBaCo
O
demonstrates a strong negative thermal expansion (NTE) which holds potential for being fabricated into composites with zero thermal expansion. The NTE was found to be intimately associated with the spontaneous magnetic ordering, known as magneto-volume effect (MVE). Here we report with compelling evidences that the continuous-like MVE in PrBaCoO is intrinsically of discontinuous character, originating from an magnetoelectric transition from an antiferromagnetic insulating large-volume (AFILV) phase to a ferromagnetic less-insulating small-volume (FLISV) phase. Furthermore, the magnetoelectric effect (ME) shows high sensitivity to multiple external stimuli such as temperature, carrier doping, hydrostatic pressure, magnetic field etc. In contrast to the well-known ME such as colossal magnetoresistance and multi-ferroic effect which involve symmetry breaking of crystal structure, the ME in the cobaltite is purely isostructural. Our discovery provides a new path way to realizing the ME as well as the NTE, which may find applications in new techniques.
Yamane, Ryo*; Komatsu, Kazuki*; Gochi, Jun*; Uwatoko, Yoshiya*; Machida, Shinichi*; Hattori, Takanori; Ito, Hayate*; Kagi, Hiroyuki*
Nature Communications (Internet), 12, p.1129_1 - 1129_6, 2021/02
Times Cited Count：21 Percentile：84.52(Multidisciplinary Sciences)Ice exhibits extraordinary structural variety in its polymorphic structures. The existence of a new form of diversity in ice polymorphism has recently been debated in both experimental and theoretical studies, questioning whether hydrogen-disordered ice can transform into multiple hydrogen-ordered phases, contrary to the known one-to-one correspondence between disordered ice and its ordered phase. Here we report a new high-pressure phase, ice XIX, which is a second hydrogen-ordered phase of ice VI. This is the first discovery to demonstrate that disordered ice undergoes different manners of hydrogen ordering. Such multiplicity can appear in all disordered ice, and it widely provides a new research approach to deepen our knowledge, for example of the crucial issues of ice: the centrosymmetry of hydrogen-ordered configurations and potentially induced (anti-)ferroelectricity. Ultimately, this research opens up the possibility of completing the phase diagram of ice.
Hattori, Takanori; Sano, Asami; Machida, Shinichi*; Ouchi, Keiichi*; Kira, Hiroshi*; Abe, Jun*; Funakoshi, Kenichi*
High Pressure Research, 40(3), p.325 - 338, 2020/09
Times Cited Count：4 Percentile：43.04(Physics, Multidisciplinary)To understand the practical effects of pressure-transmitting media (PTM) on neutron diffraction using Paris-Edinburgh presses, diffraction patterns of MgO were collected to approximately 20 GPa using PTMs of Pb, AgCl, 4:1 methano-ethanol (ME) mixture with and without heating, N, and Ar. Hydrostaticity in the sample chamber estimated from the MgO 220 peak width improves in the order of Pb, AgCl, Ar, ME mixture, N, and the heated ME mixture. Unlike previous results using a diamond anvil cell, the unheated ME mixture is superior to Ar even after freezing, probably due to the cup on the anvil face. Considering these results and the sizable coherent scattering of Ne, which would show good hydrostaticity, we conclude that the ME mixture (preferably the heated one) is the best PTM in neutron experiments up to 20 GPa, while Ar can be substituted when a sample is reactive to alcohols.
Bauer, R.*; Tse, J. S.*; Komatsu, Kazuki*; Machida, Shinichi*; Hattori, Takanori
Nature, 585(7825), p.E9 - E10, 2020/09
Times Cited Count：4 Percentile：88.42(Multidisciplinary Sciences)Pressure-induced structural transformations in deuterated crystalline ice-Ih were studied in-situ at 100 K using neutron diffraction. Very long relaxation time was allowed between small pressure increments to promote transformations to the thermodynamic stable high pressure crystalline phases. The results contradict a recent report in which measurements under similar temperature and pressure environment show successive crystal-to-crystal transformations (Tulk, et.al., Nature 2019). Instead, ice Ih was found to transform partially to an amorphous form (high density amorphous, HDA) at 1.0 GPa and then ice VII started to emerge at 1.5 GPa, a pressure substantially lower than all earlier studies. During this pressure interval, crystalline ice Ih or ice VII co-exist with HDA. The ice VII formed is stable upon pressure release down to 0.1 GPa. The very low compression rate has a profound effect on the crystallinity in the amorphous regime. Gathering all the existing experimental evidences allows an unambiguous description of the phenomenon of pressure induced amorphization. The onset of the phase transition is triggered by a shear instability of the ice lattice. The co-existence ice VII with HDA, instead of the equilibrium thermodynamic stable and proton-ordered ice-VIII under the same pressure-temperature condition reveals at low temperature there is insufficient thermal energy to overcome the substantial geometrical rearrangement from a single proton disordered H-bond network to an interpenetrating proton ordered H-bond crystalline network. Thus, leaving the proton disordered H-network intact. The analysis shows unequivocally that the structure obtained from the compression of ice is controlled by kinetics and dependent on the temperature.
Akahama, Yuichi*; Miyakawa, Masashi*; Taniguchi, Takashi*; Sano, Asami; Machida, Shinichi*; Hattori, Takanori
Journal of Chemical Physics, 153(1), p.014704_1 - 014704_5, 2020/07
Times Cited Count：7 Percentile：52.07(Chemistry, Physical)The structure refinement of black phosphorus was performed at pressures of up to 3.2 GPa at room temperature by powder neutron diffraction techniques. The bond lengths and bond angles between the phosphorus atoms at pressures were precisely determined and confirmed to be consistent with those of the previous single crystal X-ray analysis [Brown and Randqvist, Acta Cryst. 19, 684 (1965)]. Although lattice parameters exhibited an anisotropic compressibility, the covalent P1-P2 and P1-P3 bond lengths were almost independent of pressure and only the P3-P1-P2 bond angle was reduced significantly. On the basis of our results, the significant discrepancy in the bond length reported by Cartz et al. [J. Chem. Phys. 71, 1718 (1979)] has been solved. Our structural data will contribute to the elucidation of the Dirac semimetal state of black phosphorus under high pressure.
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：15.45(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：18.31(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.
Komatsu, Kazuki*; Klotz, S.*; Machida, Shinichi*; Sano, Asami; Hattori, Takanori; Kagi, Hiroyuki*
Proceedings of the National Academy of Sciences of the United States of America, 117(12), p.6356 - 6361, 2020/03
Times Cited Count：15 Percentile：61.84(Multidisciplinary Sciences)Above 2 GPa the phase diagram of water simplifies considerably and exhibits only two solid phases up to 60 GPa, ice VII and ice VIII. The two phases are related to each other by hydrogen ordering, with the oxygen sub-lattice being essentially the same. Here we present neutron diffraction data to 15 GPa which reveal that the rate of hydrogen-ordering at the ice VII-VIII transition decreases strongly with pressure to reach time scales of minutes at 10 GPa. Surprisingly, the ordering process becomes more rapid again upon further compression. We show that such an unusual change in transition rate can be explained by a slowing-down of the rotational dynamics of water molecules with a simultaneous increase of translational motion of hydrogen under pressure, as previously suspected. The observed crossover in the hydrogen dynamics in ice is likely the origin of various hitherto unexplained anomalies of ice VII in the 10-15 GPa range reported by Raman spectroscopy, X-ray diffraction, and proton conductivity.
Komatsu, Kazuki*; Klotz, S.*; Nakano, Satoshi*; Machida, Shinichi*; Hattori, Takanori; Sano, Asami; Yamashita, Keishiro*; Irifune, Tetsuo*
High Pressure Research, 40(1), p.184 - 193, 2020/02
Times Cited Count：11 Percentile：69.72(Physics, Multidisciplinary)A new high pressure cells for neutron diffraction experiments using nano-polycrystalline anvil is presented. The cell design, off-line pressure generation tests and a gas-loading procedure for this cell are described. The performance is illustrated by powder neutron diffraction patterns of ice VII to 82 GPa. We also demonstrate the feasibility of single crystal neutron diffraction experiments of Fe
O
at ambient conditions using this cell and discuss the current limitation and future developments.
without stacking disorder by evacuating hydrogen from hydrogen hydrateKomatsu, Kazuki*; Machida, Shinichi*; Noritake, Fumiya*; Hattori, Takanori; Sano, Asami; Yamane, Ryo*; Yamashita, Keishiro*; Kagi, Hiroyuki*
Nature Communications (Internet), 11, p.464_1 - 464_5, 2020/02
Times Cited Count：40 Percentile：88.26(Multidisciplinary Sciences)Water freezes below 0
C at ambient pressure ordinarily to ice I
, with hexagonal stacking sequence. Under certain conditions, ice with a cubic stacking sequence can also be formed, but ideal ice I without stacking-disorder has never been formed until recently. Here we demonstrate a route to obtain ice I without stacking-disorder by degassing hydrogen from the high-pressure form of hydrogen hydrate, C, which has a host framework isostructural with ice I. The stacking-disorder free ice I is formed from C via an intermediate amorphous or nano-crystalline form under decompression, unlike the direct transformations occurring in ice XVI from neon hydrate, or ice XVII from hydrogen hydrate. The obtained ice I shows remarkable thermal stability, until the phase transition to ice I at 250 K, originating from the lack of dislocations. This discovery of ideal ice I will promote understanding of the role of stacking-disorder on the physical properties of ice as a counter end-member of ice I.
Klotz, S.*; Komatsu, Kazuki*; Polian, A.*; Machida, Shinichi*; Sano, Asami; Iti
, J.-P.*; Hattori, Takanori
Physical Review B, 101(6), p.064105_1 - 064105_6, 2020/02
Times Cited Count：3 Percentile：23.35(Materials Science, Multidisciplinary)Manganese oxide (MnO) is a prototype of an antiferromagnetic Mott-insulator. Here we investigate the interplay of magnetic ordering and lattice distortion across the Nel temperature 
under pressure using neutron and X-ray diffraction. We find an increase of with a rate of 
= +4.5(5) K/GPa, an increase of the rhombohedral distortion 
by 
= +0.018/GPa, as well as a volume striction which is insensitive to pressure. These results allow to retrieve the dependence of the coupling constants 
and 
on interatomic distances and compare it to first-principles predictions. Antiferromagnetic diffuse scattering was observed up to 1.2 , and long-range magnetic order appears at room temperature at 42 GPa.
X-ray and neutron diffraction methodsYamashita, Keishiro*; Komatsu, Kazuki*; Hattori, Takanori; Machida, Shinichi*; Kagi, Hiroyuki*
Acta Crystallographica Section C; Structural Chemistry (Internet), 75(12), p.1605 - 1612, 2019/12
Times Cited Count：6 Percentile：56.99(Chemistry, Multidisciplinary)A crystal structure of a high-pressure phase of magnesium chloride hexahydrate (MgCl 
6HO-II) and its deuterated counterpart (MgCl 6DO-II) have been identified for the first time by in-situ single-crystal X-ray and powder neutron diffraction. The crystal structure was analyzed by the Rietveld method for the neutron diffraction pattern based on the initial structure determined by single-crystal X-ray diffraction. This high-pressure phase has a similar framework to that in the known ambient-pressure phase, but exhibits some structural changes with symmetry reduction caused by a subtle modification in the hydrogen-bond network around the Mg(HO)
octahedra. These structural features reflect the strain in the high-pressure phases of MgCl hydrates.
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：83.11(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.
