Updated on 2024/04/23

写真a

 
IIZUKA, Riko
 
Affiliation
Faculty of Education and Integrated Arts and Sciences, School of Education
Job title
Associate Professor

Research Experience

  • 2023.04
    -
    Now

    Waseda University   Faculty of Education and Integrated Arts and Sciences

  • 2020.10
    -
    Now

    The University of Tokyo   Graduate School of Science Laboratory for Earthquake Chemistry   Visiting Collaborative Researcher

  • 2021.11
    -
    2023.03

    Harvard University   Department of Earth and Planetary Sciences   Research Associate

  • 2017.01
    -
    2023.03

    Geochemical Journal   Editing secretary

  • 2016.12
    -
    2020.09

    The University of Tokyo   Graduate School of Science Laboratory for Earthquake Chemistry   Project assistant professor

  • 2013.04
    -
    2016.11

    Ehime University   Institute for Promotion of Science and Technology Geodynamics Research Center

  • 2012.04
    -
    2013.03

    The University of Tokyo   Graduate School of Science Laboratory for Earthquake Chemistry

▼display all

Professional Memberships

  • 2010
    -
    Now

    American Geophysical Union

  • 2007
    -
    Now

    日本地球惑星科学連合

  • 2007
    -
    Now

    日本地球化学会

  • 2007
    -
    Now

    日本高圧力学会

 

Papers

  • Hydrogen occupation and hydrogen-induced volume expansion in Fe<inf>0.9</inf>Ni<inf>0.1</inf>D<inf>x</inf>at high P-T conditions

    Chikara Shito, Hiroyuki Kagi, Sho Kakizawa, Katsutoshi Aoki, Kazuki Komatsu, Riko Iizuka-Oku, Jun Abe, Hirioyuki Saitoh, Asami Sano-Furukawa, Takanori Hattori

    American Mineralogist   108 ( 4 ) 659 - 666  2023.04

     View Summary

    The density of the Earth's core is several percent lower than that of iron-nickel alloy under conditions of pressure and temperature equivalent to the Earth's core. Hydrogen is one of the most promising constituents accounting for the density deficit, but hydrogen occupation sites and density decrease of iron-nickel alloy caused by hydrogenation have never been investigated. In this study, the phase relation and crystal structure of Fe0.9Ni0.1Hx(Dx) at high pressures and temperatures up to 12 GPa and 1000 K were clarified by in situ X-ray diffraction and neutron diffraction measurements. Under the P-T conditions of the present study, no deuterium atoms occupied tetragonal (T) sites of face-centered cubic (fcc) Fe0.9Ni0.1Dx, although the T-site occupation was previously reported for fcc FeHx(Dx). The deuterium-induced volume expansion per deuterium vD was determined to be 2.45(4) and 3.31(6) Å3 for fcc and hcp Fe0.9Ni0.1Dx, respectively. These vD values are significantly larger than the corresponding values for FeDx. The vD value for fcc Fe0.9Ni0.1Dx slightly increases with increasing temperature. This study suggests that only 10% of nickel in iron drastically changes the behaviors of hydrogen in metal. Assuming that vD 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.

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  • In-situ X-ray diffraction and radiography of iron–silicate–water–sulfur system simulating behaviors of light elements during early Earth’s core–mantle segregation

    Riko Iizuka-Oku, Hirotada Gotou, Akio Suzuki, Hiroyuki Kagi

    High Pressure Research   42 ( 4 ) 349 - 363  2022

     View Summary

    The Earth’s iron-rich core contains light elements. Studying the interaction of multiple light elements with iron and silicates during core–mantle segregation process in early Earth evolution has become important. In-situ X-ray diffraction and imaging observations of the iron–silicate–water–sulfur system at 5–10 GPa, up to approximately 1900°C, were used to elucidate sequential reactions: phase transformation and hydrogenation of iron, and formation of iron sulfide and silicates. The newly constructed X-ray imaging system achieved spatial resolution of approx. 10 μm for this study to show iron blob formation and motion. Sulfur distorted the iron blob shape and affected blob growth during heating by reducing the interfacial energy between molten iron and silicates. Light elements in the molten iron and the remaining silicate grains affected core–mantle segregation in the primitive Earth as temperatures increased. Carbon and silicon were incorporated into liquid Fe during later processes at higher temperatures.

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  • Behavior of light elements in iron-silicate-water-sulfur system during early Earth’s evolution

    Riko Iizuka-Oku, Hirotada Gotou, Chikara Shito, Ko Fukuyama, Yuichiro Mori, Takanori Hattori, Asami Sano-Furukawa, Ken ichi Funakoshi, Hiroyuki Kagi

    Scientific Reports   11 ( 1 )  2021.12

     View Summary

    Hydrogen (H) is considered to be one of the candidates for light elements in the Earth’s core, but the amount and timing of delivery have been unknown. We investigated the effects of sulfur (S), another candidate element in the core, on deuteration of iron (Fe) in iron–silicate–water system up to 6–12 GPa, ~ 1200 K using in situ neutron diffraction measurements. The sample initially contained saturated water (D2O) as Mg(OD)2 in the ideal composition (Fe–MgSiO3–D2O) of the primitive Earth. In the existence of water and sulfur, phase transitions of Fe, dehydration of Mg(OD)2, and formation of iron sulfide (FeS) and silicates occurred with increasing temperature. The deuterium (D) solubility (x) in iron deuterides (FeDx) increased with temperature and pressure, resulting in a maximum of x = 0.33(4) for the hydrous sample without S at 11.2 GPa and 1067 K. FeS was hardly deuterated until Fe deuteration had completed. The lower D concentrations in the S-containing system do not exceed the miscibility gap (x < ~ 0.4). Both H and S can be incorporated into solid Fe and other light elements could have dissolved into molten iron hydride and/or FeS during the later process of Earth’s evolution.

    DOI PubMed

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  • Neutron diffraction study of hydrogen site occupancy in Fe0.95Si0.05 at 14.7 GPa and 800 K

    Yuichiro Mori, Hiroyuki Kagi, Sho Kakizawa, Kazuki Komatsu, Chikara Shito, Riko Iizuka-Oku, Katsutoshi Aoki, Takanori Hattori, Asami Sano-Furukawa, Ken Ichi Funakoshi, Hirouyki Saitoh

    Journal of Mineralogical and Petrological Sciences   116 ( 6 ) 309 - 313  2021

     View Summary

    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-Fe0.95Si0.05 hydride at 14.7 GPa and 800 K. To date, this pressure condition is the highest for neutron diffraction experiments conducted at high pressure and high temperature, where crystal structure analysis has been conducted. Results of Rietveld refinement indicate hcp-Fe0.95Si0.05 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 (Fe0.95Si0.05) was negligible compared to results obtained from an earlier study of an Fe-D system (Machida et al., 2019).

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  • Crystal and Magnetic Structures of Double Hexagonal Close-Packed Iron Deuteride

    Hiroyuki Saitoh, Akihiko Machida, Riko Iizuka-Oku, Takanori Hattori, Asami Sano-Furukawa, Ken ichi Funakoshi, Toyoto Sato, Shin ichi Orimo, Katsutoshi Aoki

    Scientific Reports   10 ( 1 )  2020.12

     View Summary

    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 gigapascal (GPa). The ε′ 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 FeD0.68(1) at 673 K and 6.1 GPa and FeD0.74(1) 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 FeD1.0. In the dhcp FeD1.0 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 μB/Fe-atom aligned ferromagnetically in parallel on the Fe planes.

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  • High-pressure responses of alkali metal hydrogen carbonates, RbHCO<inf>3</inf> and CsHCO<inf>3</inf>: Findings of new phases and unique compressional behavior

    Riko Iizuka-Oku, Weibin Gui, Kazuki Komatsu, Takehiko Yagi, Hiroyuki Kagi

    Journal of Solid State Chemistry   283  2020.03

     View Summary

    High-pressure responses of RbHCO3 and CsHCO3 were characterized by in situ Raman spectroscopy and X-ray and neutron diffraction observations. RbHCO3 exhibited a monoclinic (phase IV) and a triclinic (phase V) high-pressure phase at ~0.5 ​GPa and room temperature. Increasing compression induced unique behavior in a specific cell parameter (a in phase IV or c in phase V), which first increased, and then decreased at ~1 ​GPa, likely owing to the rearrangement of Rb+ and reconfiguration of the ordered (HCO3−)2 dimers. Deuterium positions in phase IV of RbDCO3 were determined. The hydrogen bonding remained moderately strong, and possibly did not affect the phase transition despite the accompanying disordering and ordering of the dimers. CsHCO3 showed no structural change up to 5 ​GPa, suggesting that its ambient phase (isostructural to phase IV of KHCO3) was already stable at high pressure. The structural stability appeared to be systematically related to the cation size.

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  • Experimentally deformed lawsonite at high pressure and high temperature: Implication for low velocity layers in subduction zones

    Riko Iizuka-Oku, Vincent Soustelle, Nobuyoshi Miyajima, Nicolas P. Walte, Daniel J. Frost, Takehiko Yagi

    Physics of the Earth and Planetary Interiors   295  2019.10

     View Summary

    Lawsonite is considered to be one of the most likely hydrous minerals to explain the persistence of seismic low-velocity layers (LVLs) atop subducted slabs to depths of 100–250 km due mainly to the fact that it can persist to these depths, in contrast to other hydrous minerals such as antigorite. However, as it is highly anisotropic and subjected to intense deformation during subduction, further constrains on the development of lawsonite crystal preferred orientation (CPO) at high pressure and temperature are required in order to evaluate its role in slowing seismic waves. We have deformed lawsonite aggregates at 5 GPa and 500–800 °C corresponding to 150 km depth and covering temperatures for both cold and hot subduction zones. In this study, we report a new lawsonite CPO pattern resulting from dislocation creep deformation that has not been previously observed. The [100] axes concentrate into the shear direction and the [010] axes are normal to the shear plane, respectively (we refer to this as “type-1” CPO). Such CPO is consistent with our transmission electron microscope (TEM) observations identifying (010)[100] as a dominant dislocation slip-system. The seismic properties resulting from this CPO show the fast P-wave direction to be parallel to the shear direction, and the slow P-wave direction and maximum S-wave anisotropy normal to the shear plane. We performed calculation of omphacite-lawsonite aggregates using our experimental data and varied both the lawsonite contents and the slab dipping angle. Our results show that a reasonable amount of lawsonite can explain Vs reduction in the LVLs, but cannot explain the Vp reduction. However, the presence of lawsonite would induce a rotation of the fast S-wave polarization toward the trench direction as the S-wave anisotropy increases or decreases according to the lawsonite proportion, its CPO strength and the slab dipping angle. We believe that our calculation can now be used for investigation of lawsonite effect in various subductions zones.

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  • Neutron diffraction experiments on beta-CrOOD at high pressure and temperature

    Shito Chikara, Suzuki Akio, Kagi Hiroyuki, Sano―Furukawa Asami, Kakizawa Sho, Komatsu Kazuki, Aoki Katsutoshi, Iizuka Riko, Machida Shinichi, Furukawa Noboru

    Abstracts of Annual Meeting of the Geochemical Society of Japan   66 ( 0 ) 205 - 205  2019  [Refereed]

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  • Hydrogenation of iron in the early stage of Earth's evolution

    Riko Iizuka-Oku, Takehiko Yagi, Hirotada Gotou, Takuo Okuchi, Takanori Hattori, Asami Sano-Furukawa

    Nature Communications   8  2017.01

     View Summary

    Density of the Earth's core is lower than that of pure iron and the light element(s) in the core is a long-standing problem. Hydrogen is the most abundant element in the solar system and thus one of the important candidates. However, the dissolution process of hydrogen into iron remained unclear. Here we carry out high-pressure and high-temperature in situ neutron diffraction experiments and clarify that when the mixture of iron and hydrous minerals are heated, iron is hydrogenized soon after the hydrous mineral is dehydrated. This implies that early in the Earth's evolution, as the accumulated primordial material became hotter, the dissolution of hydrogen into iron occurred before any other materials melted. This suggests that hydrogen is likely the first light element dissolved into iron during the Earth's evolution and it may affect the behaviour of the other light elements in the later processes.

    DOI PubMed

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  • Development of new WC-Ni hardmetals for use in high pressure experiments

    Kouhei Wada, Takehiko Yagi, Hirotada Gotou, Riko Iizuka, Masaru Kawakami, Kozo Kitamura, Koji Hayashi

    High Pressure Research   35 ( 3 ) 263 - 272  2015.07

     View Summary

    Ultrafine-grained (0.2-0.3μm) WC-Ni hardmetals with a low Ni content (3-5wt%) were developed using new production techniques based on adding an appropriate amount of VC and Cr3C2, combined with the strong mixing of raw materials. Their uniaxial compressibility was subsequently compared with that of existing WC-Ni and WC-Co hardmetals to assess their suitability for use as anvils in various high pressure experiments, particularly those associated with neutron or magnetic studies. The ultimate compressive strength of the newly developed hardmetals was over 7.7GPa, which was higher by 1.2GPa than that of the existing WC-Ni hardmetal MF10. When these hardmetals were used as anvils, a pressure of approximately 16GPa was generated using a Paris-Edinburgh-type apparatus with φ8mm culet, thereby proving that they can allow the physical properties of various materials to be measured at higher pressures than is possible with existing hardmetals.

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  • Application of X-ray radiography to study the segregation process of iron from silicate under high pressure and high temperature

    Hirotada Gotou, Takehiko Yagi, Riko Iizuka, Akio Suzuki

    High Pressure Research   35 ( 2 ) 130 - 138  2015.04

     View Summary

    X-ray radiography was applied to observe the segregation process of iron from silicate at high pressure and high temperature in mixtures containing light elements. As the temperature of the hydrogen-containing sample increases, the molten iron becomes coherent. Small droplets of iron sink to the bottom of the chamber, where they merge into a single, large droplet. The small iron droplets exhibit complex motion, moving in random directions. Markedly different behavior is found in the sulfur-containing sample, where no clear motion of the molten iron is observed. Instead, as the sample temperature is increased, the concentration of iron near the wall of the sample chamber gradually increases. These observations demonstrate that the behavior of molten iron changes according to the dissolved elements. This X-ray radiography experiment represents a powerful technique to study the segregation process of molten iron from solid or partially molten silicate, particularly when combined with high-resolution tomography techniques.

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  • Performance of ceramic anvils for high pressure neutron scattering

    Kazuki Komatsu, Stefan Klotz, Ayako Shinozaki, Riko Iizuka, Livia E. Bove, Hiroyuki Kagi

    High Pressure Research   34 ( 4 ) 494 - 499  2014.10

     View Summary

    Three kinds of ceramics, zirconia-toughened alumina (ZTA), alumina-toughened zirconia (ATZ) and yttria-stabilized zirconia (YSZ), were tested as anvil materials, mainly for the purpose of neutron scattering study under high pressure. ZTA with non-toroidal anvil profile, having the same sample volume as conventionally used double toroidal anvils, sustained pressures up to 11.9GPa. This is comparable to anvils made of tungsten carbide (TC) with Ni binder with the same dimensions. ATZ would also be an alternative material to TC with pressure performance comparable to ZTA, whereas YSZ is much weaker than the other two ceramics. The attenuation coefficient for YSZ is significantly smaller than that of TC and similar to ZTA and ATZ, the latter being estimated by attenuation calculations. Neutron diffraction on a sample of lead in YSZ anvils as well as quasi-elastic neutron scattering on liquid water in ZTA also demonstrate the outstanding neutron transparency of these ceramics. The gain factor in count rate is up to one order of magnitude.

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    13
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  • Phase transitions and hydrogen bonding in deuterated calcium hydroxide: High-pressure and high-temperature neutron diffraction measurements

    Riko Iizuka, Kazuki Komatsu, Hiroyuki Kagi, Takaya Nagai, Asami Sano-Furukawa, Takanori Hattori, Hirotada Gotou, Takehiko Yagi

    Journal of Solid State Chemistry   218   95 - 102  2014.10

     View Summary

    In situ neutron diffraction measurements combined with the pulsed neutron source at the Japan Proton Accelerator Research Complex (J-PARC) were conducted on high-pressure polymorphs of deuterated portlandite (Ca(OD)2) using a Paris-Edinburgh cell and a multi-anvil press. The atomic positions including hydrogen for the unquenchable high-pressure phase at room temperature (phase II′) were first clarified. The bent hydrogen bonds under high pressure were consistent with results from Raman spectroscopy. The structure of the high-pressure and high-temperature phase (Phase II) was concordant with that observed previously by another group for a recovered sample. The observations elucidate the phase transition mechanism among the polymorphs, which involves the sliding of CaO polyhedral layers, position modulations of Ca atoms, and recombination of Ca-O bonds accompanied by the reorientation of hydrogen to form more stable hydrogen bonds. © 2014 Elsevier Inc.

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  • Site occupancy of interstitial deuterium atoms in face-centred cubic iron

    Akihiko Machida, Hiroyuki Saitoh, Hidehiko Sugimoto, Takanori Hattori, Asami Sano-Furukawa, Naruki Endo, Yoshinori Katayama, Riko Iizuka, Toyoto Sato, Motoaki Matsuo, Shin Ichi Orimo, Katsutoshi Aoki

    Nature Communications   5  2014

     View Summary

    Hydrogen composition and occupation state provide basic information for understanding various properties of the metal-hydrogen system, ranging from microscopic properties such as hydrogen diffusion to macroscopic properties such as phase stability. Here the deuterization process of face-centred cubic Fe to form solid-solution face-centred cubic FeD x is investigated using in situ neutron diffraction at high temperature and pressure. In a completely deuterized specimen at 988 K and 6.3 GPa, deuterium atoms occupy octahedral and tetrahedral interstitial sites with an occupancy of 0.532(9) and 0.056(5), respectively, giving a deuterium composition x of 0.64(1). During deuterization, the metal lattice expands approximately linearly with deuterium composition at a rate of 2.21 Å3 per deuterium atom. The minor occupation of the tetrahedral site is thermally driven by the intersite movement of deuterium atoms along the 111 direction in the face-centred cubic metal lattice.

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  • Crystal structure of the high-pressure phase of calcium hydroxide, portlandite: In situ powder and single-crystal X-ray diffraction study

    Riko Iizuka, Takehiko Yagi, Kazuki Komatsu, Hirotada Gotou, Taku Tsuchiya, Keiji Kusaba, Hiroyuki Kagi

    American Mineralogist   98 ( 8-9 ) 1421 - 1428  2013

     View Summary

    The crystal structure of a high-pressure phase of calcium hydroxide, Ca(OH)2 (portlandite), was clarified for the first time using the combination of in situ single-crystal and powder X ray diffraction measurements at high pressure and room temperature. A diamond-anvil cell with a wide opening angle and cell-assembly was improved for single-crystal X ray diffraction experiments, which allowed us to successfully observe Bragg reflections in a wide range of reciprocal space. The transition occurred at 6 GPa and the crystal structure of the high-pressure phase was determined to be monoclinic at 8.9 GPa and room temperature [I121; a = 5.8882(10), b = 6.8408(9), c = 8.9334(15) Å, β = 104.798(15)°]. The transition involved a decrease in molar volume by approximately 5.8%. A comparison of the structures of the low- and high-pressure phases indicates that the transition occurs by a shift of CaO 6 octahedral layers in the a-b plane along the a-axis, accompanied by up-and-down displacements of Ca atoms from the a-b plane. The crystal structure of this high-pressure phase is considered to be an intermediate state between the low-pressure phase and the high-pressure-high-temperature phase. The complicated diffraction patterns of the high-pressure phase suggest that the phase transition occurred toward three directions around the c-axis of the low-pressure phase. This explains the difficulties encountered in previous structural analyses. The present results will provide key information for discussing the behavior of hydrogen bonds in these hydrous minerals under pressure.

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  • An opposed-anvil-type apparatus with an optical window and a wide-angle aperture for neutron diffraction

    Riko Iizuka, Takehiko Yagi, Hirotada Gotou, Kazuki Komatsu, Hiroyuki Kagi

    High Pressure Research   32 ( 3 ) 430 - 441  2012.09

     View Summary

    We designed new anvil assemblies for acquiring high-quality neutron diffraction data and ruby fluorescence spectra inside a sample chamber. The conical aperture of Ni-binded WC anvils was expanded by a factor of two. A hybrid gasket made of TiZr- and Al-alloy was developed to prevent outward extrusion. A small and optically transparent window of moissanite was introduced to allow for the determination of pressure and hydrostaticity by measurement of ruby fluorescence spectra. High pressure-generation tests that make use of Bi electrical conductivity and ruby pressure markers revealed that pressure could be determined over 10GPa. In situ synchrotron X-ray diffraction experiments were also carried out using NaCl as the pressure calibrants. The maximum pressure achieved was approximately 13GPa. The neutron diffraction intensity from the newly generated anvil assemblies was 2.5-3.0 times greater than that using the standard toroidal anvil assemblies used previously. © 2012 Copyright Taylor and Francis Group, LLC.

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  • Pressure responses of portlandite and H-D isotope effects on pressure-induced phase transitions

    Riko Iizuka, Hiroyuki Kagi, Kazuki Komatsu, Daichi Ushijima, Satoshi Nakano, Asami Sano-Furukawa, Takaya Nagai, Takehiko Yagi

    Physics and Chemistry of Minerals   38 ( 10 ) 777 - 785  2011.12

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    The pressure responses of portlandite and the isotope effect on the phase transition were investigated at room temperature from single-crystal Raman and IR spectra and from powder X-ray diffraction using diamond anvil cells under quasi-hydrostatic conditions in a helium pressure-transmitting medium. Phase transformation and subsequent peak broadening (partial amorphization) observed from the Raman and IR spectra of Ca(OH)2 occurred at lower pressures than those of Ca(OD)2. In contrast, no isotope effect was found on the volume and axial compressions observed from powder X-ray diffraction patterns. X-ray diffraction lines attributable to the high-pressure phase remained up to 28.5 GPa, suggesting no total amorphization in a helium pressure medium within the examined pressure region. These results suggest that the H-D isotope effect is engendered in the local environment surrounding H(D) atoms. Moreover, the ratio of sample-to-methanol-ethanol pressure medium (i.e., packing density) in the sample chamber had a significant effect on the increase in the half widths of the diffraction lines, even at pressures below the hydrostatic limit of the pressure medium. © 2011 Springer-Verlag.

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  • A simple opposed-anvil apparatus for high pressure and temperature experiments above 10 GPa

    Hirotada Gotou, Takehiko Yagi, Taku Okada, Riko Iizuka, Takumi Kikegawa

    High Pressure Research   31 ( 4 ) 592 - 602  2011.12

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    A new opposed-anvil high pressure and temperature apparatus was developed based on the Drickamer-type apparatus. Various improvements were made to increase the sample volume and to generate high pressure and temperature stably and easily. By optimizing components such as the anvil, heater, and gasket, large sample volumes of about 4mm 3 (∼10 3 times more than that previously obtained with our previous apparatus) were achieved, with compact and light apparatus (outer diameter φ 40mm; height 31mm; weight 300g). Pressures and temperatures up to about 15GPa and 1700K can routinely and stably be achieved by using this assembly. In order to extend the pressure range further, sintered diamond was used as an anvil material. As a result, pressures and temperatures of around 38GPa and 1400K were achieved, although the sample volume was decreased to about 1.3∼10 -1mm 3. © 2011 Taylor and Francis.

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  • A design of backing seat and gasket assembly in diamond anvil cell for accurate single crystal x-ray diffraction to 5 GPa

    K. Komatsu, H. Kagi, T. Yasuzuka, T. Koizumi, R. Iizuka, K. Sugiyama, Y. Yokoyama

    Review of Scientific Instruments   82 ( 10 )  2011.10

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    We designed a new cell assembly of diamond anvil cells for single crystal x-ray diffraction under pressure and demonstrate the application of the cell to the crystallographic studies for ice VI and ethanol high-pressure (HP) phase at 0.95(5) GPa and 1.95(2) GPa, respectively. The features of the assembly are: (1) the platy anvil and unique-shaped backing seat (called as Wing seat) allowing the extremely wide opening angle up to ±65°, (2) the PFA-bulk metallic glass composite gasket allowing the easy attenuation correction and less background. Thanks to the designed assembly, the Rint values after attenuation corrections are fairly good (0.0125 and 0.0460 for ice VI and ethanol HP phase, respectively), and the errors of the refined parameters are satisfactory small even for hydrogen positions, those are comparable to the results which obtained at ambient conditions. The result for ice VI is in excellent agreement with the previous study, and that for ethanol HP phase has remarkable contributions to the revision to its structure; the H12 site, which makes gauche molecules with O1, C2, and C3 sites, may not exist so that only trans conformers are present at least at 1.95(2) GPa. The accurate intensities using the cell assembly allow us to extract the electron density for ethanol HP phase by the maximum entropy method. © 2011 American Institute of Physics.

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  • Hydrogen motions of Mg(OD)(2) and Ca(OD)(2) at several temperatures

    Takaya Nagai, Asami Sano-Furukawa, Riko Iizuka, Bryan C. Chakoumakos, Jaime A. Fernandez-Baca

    ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES   67   C241 - C241  2011

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  • Infrared absorption spectra of δ-AlOOH and its deuteride at high pressure and implication to pressure response of the hydrogen bonds

    H. Kagi, D. Ushijima, A. Sano-Furukawa, K. Komatsu, R. Iizuka, T. Nagai, S. Nakano

    Journal of Physics: Conference Series   215  2010

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    Infrared absorption spectra of δ-AlOOH and its deuterated form (δ-AlOOD) were measured at high pressure using a diamond anvil cell under a quasi-hydrostatic pressure condition using helium as a pressure-transmitting medium. Two absorption bands at 1180 cm-1and 1330 cm-1 involving vibrations of hydrogen and oxygen atoms shifted to higher frequencies with increasing pressure up to 10 and 12 GPa for δ-AlOOH and δ-AlOOD, respectively. In contrast, at higher pressures the two bands did not shift so much. The pressure-response on the infrared spectra has a close relationship to the symmetrization of the hydrogen bonds and change in the compressibility which was observed from X-ray diffraction measurements. © 2010 IOP Publishing Ltd.

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  • Comparing ruby fluorescence spectra at high pressure in between methanol-ethanol pressure transmitting medium and its deuteride

    R. Iizuka, H. Kagi, K. Komatsu

    Journal of Physics: Conference Series   215  2010

     View Summary

    Ruby fluorescence spectra were statistically compared in between a 4:1 methanol-ethanol and its deuterated mixture under high pressure in the DAC. It was confirmed that the isotope substitution in the pressure transmitting media results in no distinctive difference in the peak shape and pressure shift of the R1 and R2 lines in the ruby fluorescence spectra up to around 25 GPa. These results suggest that the pressure-induced solidification/glass transition between these hydrogenated and deuterated liquids has no isotopic effect within experimental uncertainties. © 2010 IOP Publishing Ltd.

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  • Experimental observations of H-bonding symmetrization of delta-AIOOH

    H. Kagi, D. Ushijima, A. Sano-Furukawa, K. Komatsu, R. Iizuka, T. Nagai, S. Nakano

    GEOCHIMICA ET COSMOCHIMICA ACTA   73 ( 13 ) A613 - A613  2009.06

  • 含水地球深部鉱物の高圧下での水素結合対称化と同位体効果

    鍵 裕之, 牛嶋 大地, 佐野 亜沙美, 小松 一生, 飯塚 理子, 中野 智志

    日本地球化学会年会要旨集   56   315 - 315  2009

     View Summary

    下部マントルまで水を運搬する可能性が示唆されている、含水アルミニウム水酸化物delta-AlOOHについて、疑似静水圧条件で圧縮率の精密測定と赤外吸収スペクトルの観察を行い、水素結合の対称化の兆候を観察した。また、圧力応答に水素の同位体効果が見られた。

    DOI CiNii

  • Change in compressibility of δ-AlOOH and δ-AlOOD at high pressure: A study of isotope effect and hydrogen-bond symmetrization

    Asami Sano-Furukawa, Hiroyuki Kagi, Takaya Nagai, Satatoshi Nakano, Satatoshi Fukura, Daichi Ushijima, Riko Iizuka, Eiji Ohtahtahtani, Takehehiko Yagi

    American Mineralogist   94 ( 8-9 ) 1255 - 1261  2009

     View Summary

    The compression behaviors of δ-AlOOH and δ-AlOOD were investigated under quasi-hydrostatic conditions at pressures up to 63.5 and 34.9 GPa, respectively, using results from synchrotron X-ray diffraction experiments conducted at ambient temperature. Because of the geometric isotope effect, at ambient pressure, the a and b axes of δ-AlOOD, which define the plane in which the hydrogen bond lies, are longer than those of δ-AOOH. Under increasing pressure, the a and b axes of δ-AlOOH stiffen at 10 GPa, although the c axis shows no marked change. Identical behavior was found in δ-AlOOD, but the change in compressibility was observed at a slightly higher pressure of 12 GPa. Axial ratios a/c and b/c first decrease rapidly with increasing pressure, then begin to increase at pressures >10 GPa in δ-AlOOH and >12 GPa in δ-AlOOD. At these pressures, the pressure dependence of a/b also changes from increasing to decreasing. The unit-cell volumes of δ-AlOOH and δ-AlOOD become slightly less compressible at high pressures. Assuming K0' = 4, the calculated bulk moduli of δ-AlOOH below and above 10 GPa are 152(2) and 219(3) GPa, respectively. Those of δ-AlOOD below and above 12 GPa are 151(1) and 207(2) GPa, respectively.

    DOI

    Scopus

    85
    Citation
    (Scopus)
  • Micro-pellet method for infrared absorption spectroscopy using a diamond anvil cell under a quasi-hydrostatic condition

    Hiroyuki Kagi, Daichi Ushijima, Riko Iizuka, Satoshi Nakano, Takaya Nagai

    High Pressure Research   28 ( 3 ) 299 - 306  2008.09

     View Summary

    A method was proposed for measuring infrared absorption spectra at high pressure under quasi-hydrostatic pressure conditions. Two KBr micro-pellets were prepared as samples, and reference materials were charged in a diamond anvil cell, applying helium as the pressure-transmitting medium. Using this method, the quasi-hydrostatic pressure condition was retained up to approximately 20GPa. Furthermore, hydrostaticity was much better than conventional pressure-transmitting media used for infrared spectroscopy. Infrared absorption spectra of α -FeOOH at high pressure were measured using the KBr micro-pellet method with a helium pressure-transmitting medium. Downshift of the OH stretching vibration was observed with increasing pressure. Use of the KBr micro-pellet method for infrared absorption spectroscopy at high pressure is a complementary experimental technique to neutron diffraction at high pressure for studying the pressure response of hydrogen bonds.

    DOI

    Scopus

    6
    Citation
    (Scopus)

▼display all

Presentations

  • Neutron diffraction experiments on beta-CrOOD at high pressure and temperature

    Shito Chikara, Suzuki Akio, Kagi Hiroyuki, Sano―Furukawa Asami, Kakizawa Sho, Komatsu Kazuki, Aoki Katsutoshi, Iizuka Riko, Machida Shinichi, Furukawa Noboru

    Abstracts of Annual Meeting of the Geochemical Society of Japan  GEOCHEMICAL SOCIETY OF JAPAN

    Presentation date: 2019

    Event date:
    2019
     
     

     View Summary

    <p></p>

  • In-situ synchrotron X-ray imaging on Fe-hydrous silicate under high pressure and high temperature: Implication for Earth's evolution process

    Iizuka―Oku Riko, Gotou Hirotada, Suzuki Akio, Kagi Hiroyuki

    Abstracts of Annual Meeting of the Geochemical Society of Japan  GEOCHEMICAL SOCIETY OF JAPAN

    Presentation date: 2019

    Event date:
    2019
     
     
  • Pressure-induced Phase Transition of Alkali Metal Hydrogen Carbonates

    Gui Weibin, Iizuka-Oku Riko, Kagi Hiroyuki

    Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences  Japan Association of Mineralogical Sciences

    Presentation date: 2017

    Event date:
    2017
     
     

     View Summary

    Crystal structures of alkali metal hydrogen carbonates are affected by pressure. Previous studies showed that KHCO3 has a phase transition at around 2.8 GPa, room temperature. This study discovered that RbHCO3 transformed into a high-pressure phase at around 0.5 GPa, room temperature. As for CsHCO3, no phase transition was observed up to 5 GPa. These results suggested that the pressure-induced behaviors of alkali metal hydrogen carbonates were systematically related to their cation radii.

  • Studies on thermal expansion mechanism of portlandite by neutron diffraction measurements

    Nagai Takaya, Sano-Furukawa Asami, Iizuka Riko, Kagi Hiroyuki

    Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences  Japan Association of Mineralogical Sciences

    Presentation date: 2012

    Event date:
    2012
     
     

     View Summary

    Mechanism of thermal expansion of portlandite will be discussed on the basis of the crystal struture parameters determinded by Rietveld analysis for powder neutron diffraction data obtained at the US-Japan Wide-Angle Neutron Diffractometer (WAND) of the High Flux Isotope Reactor in Oak Ridge National Laboratory, USA.

  • Isotope effects on pressure-response of dense hydrous materials

    Kagi Hiroyuki, Iizuka Riko, Komatsu Kazuki, Sano Asami

    Abstracts of Annual Meeting of the Geochemical Society of Japan  GEOCHEMICAL SOCIETY OF JAPAN

    Presentation date: 2011

    Event date:
    2011
     
     
  • Neutron diffraction studies on Mg(OD)2 at high temperature

    NAGAI TAKAYA, SANO-FURUKAWA ASAMI, IIZUKA RIKO, KAGI HIROYUKI

    Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences  Japan Association of Mineralogical Sciences

    Presentation date: 2011

    Event date:
    2011
     
     

     View Summary

    We carried out in situ neutron diffraction measurements on Mg(OD)2 at several temperatures from 200 K to 600 K. Since no diffraction peaks of MgO could be observed in obtained neutron diffraction patterns in this study, the samples of Mg(OD)2 were stable up to 600 K under the present conditions. Both unit-cell parameters of a- and c-axis anisotropically increase on heating. The detailed structure parameters such as atomic coordinates were refined by the Rietveld method by using a program GSAS. Calculated selected bond lengths change monotonically with increasing temperature, but the data obtained at 600 K which is the maximum temperature in this study seem to apart from those trends.

  • Pressure-induced changes of hydrogen bonding and crystal structure of hemimorphite

    YAMAGUCHI Yu, IIZUKA Riko, KOMATSU Kazuki, KAGI Hiroyuki

    Presentation date: 2010.10

    Event date:
    2010.10
     
     
  • Pressure-induced changes of hydrogen bonding and crystal structure of hemimorphite

    YAMAGUCHI YU, IIZUKA RIKO, KOMATSU KAZUKI, KAGI HIROYUKI

    Abstracts of Annual Meeting of the Geochemical Society of Japan  GEOCHEMICAL SOCIETY OF JAPAN

    Presentation date: 2010

    Event date:
    2010
     
     
  • 炭酸水素カリウムの圧力誘起構造相転移のその場観察と同位体効果の探索

    飯塚 理子, 小松 一生, 鍵 裕之

    日本地球化学会年会要旨集  一般社団法人日本地球化学会

    Presentation date: 2007

    Event date:
    2007
     
     

     View Summary

    含水鉱物の圧縮挙動は物質の構造変化に直接的に関連し、地球内部での大規模現象における有用な情報を与えうることから、近年、水素結合を含む物質の圧力応答に関する研究が進められてきた。常圧でも強い水素結合をもつ炭酸水素カリウムKHCO3は、結晶構造中で2つのHCO3イオンが水素結合によって二量体を形成している。この二量体の配向秩序が変化することで、圧力や温度誘起による相転移が起こる。しかし、この物質の相転移圧力への同位体効果はいまだ明らかではない。本研究では、DACを用いた、単結晶KHCO3とKDCO3の圧力相転移前後のラマンスペクトルと結晶の外形の変化の精密なその場観察から、圧力誘起相転移における同位体効果の存在の確認と相転移メカニズムの検証を行った。

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Research Projects

  • アルカリケイ酸塩を介した下部マントル深部への希ガス貯蔵

    日本学術振興会  科学研究費助成事業 基盤研究(C)

    Project Year :

    2023.04
    -
    2026.03
     

    飯塚 理子

  • Material Science of Hydrogen in the deep earth and planets

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)

    Project Year :

    2018.06
    -
    2023.03
     

  • Behaviors of light elements during early Earth's formation from high-pressure and high-temperature experiments

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Early-Career Scientists

    Project Year :

    2018.04
    -
    2022.03
     

    Iizuka Riko

     View Summary

    The Earth’s core mainly consists of iron (Fe) and is considered to contain light elements (H, C, O, Si, S) to explain the density deficit compared to pure iron. Hydrogen (H) is one of the promising candidates. However, its amount dissolved in the core and the process are still unknown due to the difficulty in detecting the lightest element via X-ray and obtaining the unquenchable hydrides.
    In this study, we investigated the effect of sulfur (S) on the hydrogenation of iron using in-situ neutron diffraction observations at high pressure and high temperature. The obtained H solubility of Fe and FeS in the sample simulating the primitive Earth indicated that iron hydride was formed by the reaction of Fe and water, while FeS is hardly hydrogenated. Both H and S can be incorporated into solid iron, whereas the other light elements could have dissolved into molten iron hydrides and FeS during the later process of the Earth’s evolution.

  • 中性子回折用超高圧装置の開発と高圧下における水素結合系物質の挙動の解明

    日本学術振興会  科学研究費助成事業 特別研究員奨励費

    Project Year :

    2013.04
    -
    2017.03
     

    飯塚 理子

     View Summary

    地球深部に遍在する水(水素)の存在状態を明らかにすることは、地球内部のダイナミクスや物質循環を理解する上で非常に重要である。本研究では水素を観察できる中性子線を用いることにより、地球深部に相当する高圧条件下において水や水素がどのような振る舞いをするのかを観察し、地球内部物質に対するこれらの影響を明らかにする手がかりを得ることを目的として、高温高圧中性子回折実験用に新たに開発したセルを導入し、研究を遂行した。
    最終年度(出産育児により一時中断後研究を再開した残り2ヶ月間)は、主に解析と今後に向けた追試実験を行った。水素の振る舞いを直接観察できる中性子回折の手法を用いて鉄-シリケイト-水系の地球形成初期に集積した物質をモデル化した出発試料に対して高温高圧下その場観察を行い、高温高圧下で含水鉱物が脱水してできた水と固体の鉄とが反応して、鉄水素化物が生成する様子をリアルタイムでとらえることに成功した。これにより、鉄と鉄が水素化物となって有意に水を取り込むことが明らかになり、原始地球で始源物質が集積していく初期段階で、水素は鉄へと溶け込み始めていたことが示唆された。この研究結果は学術雑誌に論文として出版され、地球核に取り込まれた軽元素の問題に対して、これまで種々の実験が行われてきた純鉄とケイ酸塩の系だけではなく、水素化した鉄とケイ酸塩間での軽元素の分配を調べていくことの重要性を投げかけた。高圧下での中性子その場観察では、高温高圧が長時間安定に発生でき、かつ、大容量の試料でシグナル強度を稼げることが望ましい。そのためには、本研究で開発・導入した新型6-6セルに対して、高温高圧下での圧力抜け及びアンビルセルからの中性子の吸収を軽減などの課題を克服していく必要がある。今後の展望として、更なるセルの改良によりアセンブリの最適化を図っていくための基礎固めが本研究によってなされたと言える。

  • Study of hydrogen in the Earth's core based on the high-pressure neutron experiments

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

    Project Year :

    2013.04
    -
    2016.03
     

    Yagi Takehiko, IIZUKA-OKU Riko, GOTOU Hirotada, OKUCHI Takuo, INOUE Toru, HATTORI Takanori, SANO Asami

     View Summary

    In order to clarify the behavior of hydrogen in the early stage of Earth’s evolution, which is regarded as one of the strong candidates of light elements in the core, a first neutron experiments under high pressures and temperatures on a mixture of iron and hydrous minerals were performed at J-PARC, Ibaraki. The results suggest that when primordial materials such as hydrous meteorite and siderites were accumulated, molten iron hydride was formed first with increasing temperature. It is likely that other light elements were dissolved into molten iron hydride after that.

  • Synthesis and search of a new functional diamond using ultra-high pressure and temperature synthesis method.

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Project Year :

    2012.04
    -
    2015.03
     

    GOTOU Hirotada, HAMANE Daisuke, ISOBE Masahiko, IIZUKA Riko

     View Summary

    In this study, impurity-doped diamonds were synthesized using high pressure and temperature synthesis method with pressure higher than that employed conventionally. Li- and Mg- doped diamonds were successfully prepared; however, to synthesize Li-doped diamond, Li-GIC (Graphite intercalation compound) is need as a starting material, while the synthesis of the Mg-doped diamond requires the use of a catalyst. In addition, the formation mechanism of Mg-doped diamond was investigated by in-situ X-ray diffraction experiment.

  • 高圧下中性子回折その場観察による金属水酸化物の水素結合の圧力応答の解明

    日本学術振興会  科学研究費助成事業 研究活動スタート支援

    Project Year :

    2012.08
    -
    2014.03
     

    飯塚 理子

     View Summary

    本研究は、大強度陽子加速器施設J-PARC(茨城県東海村)にある高圧中性子回折実験用ビームラインにおいて、含水鉱物の高圧下における水素結合の挙動と水素原子の位置を明らかにすることが目的である。そこで、まず短時間で高S/N比を持つ良質な中性子回折パターンを得ることができる高圧発生装置を改良し、含水鉱物のアナログ物質として知られる水酸化カルシウムCa(OD)2の新高圧相について、高圧下での中性子その場観察を世界で初めて試みた。
    平成24年度は主に装置の開発を進めてきた。中性子実験のスケジュール調整と装置開発面での計画延長の必要が生じたことから、平成24年度経費の一部を25年度に繰越した。これにより、2013年内に申請者自身が実験責任者として採択された実験課題に沿って、J-PARCにある高温高圧ビームラインPLANET(BL11)にて中性子実験が実現した。また2013年夏には、フランスの中性子実験施設に遠征し、開発された本装置の一部をさらなる改良・実用化した実験にも参加し、非常に有益な機会も得た。J-PARCの実験では、申請者がこれまでに開発してきた高圧発生装置を持ち込み、この装置の有用性を示すことができたと同時に、Ca(OD)2の室温高圧相の回折パターンを測定することに初めて成功し、結晶構造と水素原子位置の詳細が明らかになった。また、別に6軸プレスを用いた中性子実験から得られたCa(OD)2の高温高圧相の結果も併せて、高圧相の相関係と水素結合の変化について考察し、同等の構造をもつ水酸化物の高圧下での振る舞いに関して、体系的な理解につながる知見を得た。この成果報告として、国内外の学会で発表を行った。さらに、学術雑誌Journal of Solid State Chemistryに論文を投稿し、非常によいコメントをいただき、現在そのリバイス段階にある。

  • 中性子回析用超高圧セルの開発と水素結合の圧力応答のその場観察

    日本学術振興会  科学研究費助成事業 特別研究員奨励費

    Project Year :

    2010
    -
    2011
     

    飯塚 理子

     View Summary

    水素結合を基調とする物質の圧力誘起相転移における結晶構造変化を詳細に調べることは、物質科学の分野に新しい知見を与えるだけでなく、地球内部の理解を深めることにもつながる。本研究では、地球深部まで水を運搬する含水鉱物のモデル物質とされている、水酸化カルシウムに着目し、この物質の未知の室温高圧相の構造を同定することを目的として、ダイヤモンドアンビルセルを用いた単結晶X線回折実験による高圧下その場観察を行った。また、解析に必要な十分な数の反射をより多く得るために、広い開口角を持つダイヤモンドアンビルセルへの改良も行った。
    片方のダイヤモンドの先端面中心にエキシマレーザーを用いて底面が平らな凹みを掘った、"Radial-DAC"を開発し実験を行った。この凹みの中に単結晶試料を入れ、加圧軸に垂直に開いた窓を通して、入射X線を照射し回折X線を検出する測定系で、イメージングプレートを用いて高圧相のブラッグ反射を測定した。この新しい高圧装置と高輝度なX線を組み合わせて得られた振動写真の解析から、室温高圧相の構造とその相転移メカニズムが明らかになった。これは、これまでの先行研究では非晶質化すると考えられていた水酸化カルシウムの圧縮挙動における新しい発見であり、大変重要な成果であると言える。
    将来的には、この水酸化カルシウムの高圧相の水素位置と低圧相からの水素結合の変化の詳細を知るために、大強度陽子加速器施設J-PARCのパルス中性子を利用した、高圧下での粉末中性子回折実験の実現を目指している。昨年度、および本年度前期には、中性子回折と分光測定の同時観察を可能にするためのアンビルとガスケット部分の改良も行った。これにより、静水圧のよい条件下で、水酸化カルシウムの室温高圧相の回折パターンをより短時間で測定することが可能なセルの準備が整った。

  • Materials science study of the Earth's core based on the high-pressure and high-temperature experiments under core condition using polycrystalline diamond

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

    Project Year :

    2007
    -
    2009
     

    YAGI Takehiko, OKADA Taku, SUEDA Yuichiro, IRIFUNE Tetsuo

     View Summary

    Experimental techniques to make X-ray diffraction study under the condition of the Earth's core was developed using diamond anvil by employing both nanocrystalline diamond and single crystal diamond as anvil materials. Reaction of iron and xenon was studied up to 155GPa and 3000K using this technique. No reaction between these two materials was observed up to the highest pressure, which suggest that the origin of the "missing xenon" should be found somewhere outside of the core.

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Misc

  • Effect of Sulfur on Hydrogenation of Metallic Iron and Evolution of the Earth's Core

    Riko Iizuka-Oku, Hiroyuki Kagi

    Materia Japan   61 ( 4 ) 202 - 209  2022.04

    Article, review, commentary, editorial, etc. (scientific journal)  

    DOI

  • In-Situ Neutron Diffraction of Iron Hydride in Iron-silicate-water System under High Pressure and High Temperature Condition

    Riko Iizuka-Oku, Takehiko Yagi, Hirotada Gotou, Takuo Okuchi, Takanori Hattori, Asami Sano-Furukawa

    hamon   27 ( 3 ) 104 - 108  2017

    Article, review, commentary, editorial, etc. (scientific journal)  

    DOI

  • Development of opposed-type anvils with wide-angle aperture and investigation of pressure-induced phase transition of Ca(OD)<inf>2</inf>

    Riko Iizuka-Oku

    Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu   26 ( 2 ) 128 - 139  2016

    Book review, literature introduction, etc.  

     View Summary

    Newly designed opposed-type anvil assemblies were developed for acquiring high signal intensity of neutron diffraction data and ruby fluorescence spectra. Ni-binded WC anvils with a wide aperture angle, which were combined with a hybrid gasket made of TiZr and Al-alloy, achieved nearly ~15 GPa at room temperature. The neutron diffraction intensity was 2.5-3.0 times greater than that using the conventional toroidal anvil assemblies. The performance test of these new anvil assemblies confirms that sufficient quality diffraction data can be obtained. Using these assemblies, high-pressure behavior of hydrogen bond in Ca(OD)2was investigated at PLANET beamline, J-PARC.

    DOI

  • 世界に羽ばたく理学博士 第10回

    飯塚, 理子, 岡, 光夫

    東京大学理学系研究科・理学部ニュース   45 ( 2 ) 8 - 9  2013.07

     View Summary

    ドイツ バイロイトより地球科学の調べ/カリフォルニアで宇宙科学探査を楽しむ

    CiNii

  • Pressure Responses of Hydrogen Bonds in Hydrous Minerals –Pressure-induced Phase Transition in Ca(OH)2 and Technical Development of High Pressure Neutron Experiments–

    Iizuka Riko

    Chikyukagaku   46 ( 3 ) 186 - 187  2012

    DOI CiNii

  • Report on Study of High-Pressure Geophysics at American Geophysical Union 2010 Fall Meeting

    IIZUKA Riko

    The Review of High Pressure Science and Technology   21 ( 3 ) 232 - 233  2011

    DOI CiNii

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Syllabus

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Sub-affiliation

  • Faculty of Science and Engineering   Graduate School of Creative Science and Engineering

Internal Special Research Projects

  • 高温高圧下での中性子回折実験による原始地球の軽元素取り込みの解明

    2023  

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    本課題では、地球深部に存在する鉄化合物の中に取り込まれる軽水素の挙動を探究することを主な目的としている。地球の核を構成する重要な要素である鉄と軽元素との相互作用は、地球の内部構造やダイナミクスに関する理解を深める上で重要な意味を持つ。特に、地球コアに溶け込んでいる軽元素の中で水素は最も有力な候補の一つとされており、その存在形態を解明することは、地球の磁場生成や深部における物質循環の理解に対して新たな視点を提供する。本研究では、放射光X線とパルス中性子線を組み合わせたマルチ量子ビーム技術を用いた実験的アプローチにより、高温高圧条件下での鉄と水素の反応機構についての詳細なデータを取得し、地球内部における軽水素の存在形態を明らかにすることを目指した。具体的な実験手法として、まず放射光を用いた高温高圧下でのX線回折その場観察を行った。ダイヤモンドアンビルセルやマルチアンビルプレスを用いて、10-15 GPa、1000-3000Kの極端な環境下で水や水酸化物を水素源にして、炭酸鉄と水(水素)との反応を調査した。この過程で、未知の副生成物の出現を観測し、さらに回収した試料を電子顕微鏡で観察することで、金属化した形跡や鉄の酸化還元状態の変化による析出などの現象を確認した。これまでの結果から、地球深部の条件下で鉄がどのように水素と反応するか、そしてその過程でどのような物質が生成されるのかについて、貴重な洞察を得ることができた。しかし、新たに観測された生成物の詳細な結晶構造や組成については、まだ同定されていない。そのため、今後はさらなる分析と実験を重ね、未知の化合物の特定を進める予定である。最終目標として、高温高圧下でのその場観察により、鉄と水素の相互作用に他の軽元素がどのように影響を及ぼすかを明らかにする。本研究は、地球惑星科学や物質科学の分野においても重要な意義を持つと期待される。