Researcher Profile and Settings

Affiliation

• Faculty of Science　Earth and Planetary Sciences　Earth and Planetary System Science

Job Title

• Professor

Degree

• Doctor of Science（The University of Tokyo）

URL

http://www.sci.hokudai.ac.jp/nagai-t-web1/

Research funding number

• 20243131

J-Global ID

• 200901080785443260

Research Interests

• 中性子回折   X線回折   反応速度   固溶体   ペロブスカイト   Hydrous minerals   High pressure and high temperature   Physics and Chemistry of Minerals   Crystallography   Mineralogy   

Research Areas

• Natural sciences / Solid earth science
• Nanotechnology/Materials / Crystal engineering
• Nanotechnology/Materials / Basic physical chemistry

Educational Organization

•  Bachelor's degree program　School of Science
•  Master's degree program　Graduate School of Science
•  Doctoral (PhD) degree program　Graduate School of Science

Academic & Professional Experience

• 2023/03 - Today Hokkaido University Graduate School of Science Dean of Graduate School of Science
• 2011/10 - Today Hokkaido University Faculty of Science Professor
• 2021/04 - 2023/03 Hokkaido University Graduate School of Science Dean of Graduate School of Science
• 2007/04 - 2011/09 Hokkaido University Faculty of Science, Department of Natural History Sciences
• 2003/11 - 2007/03 北海道大学大学院理学研究科 助教授
• 1996/04 - 2003/10 Osaka University Graduate School of Science
• 1994/04 - 1996/03 Osaka University School of Science
• 1992/02 - 1994/03 大阪大学教養部 助手

Education

• 1990/04 - 1992/01  The University of Tokyo
• 1988/04 - 1990/03  The University of Tokyo
• 1984/04 - 1988/03  The University of Tokyo  Faculty of Science  Department of Geological Sciences

Association Memberships

• Mineralogical Society of America   The Japanese scoeity of neutron science   JAPAN ASSOCIATION OF MINERALOGICAL SCIENCES   THE JAPAN SOCIETY OF HIGH PRESSURE SCIENCE AND TECHNOLOGY   American Geophysical Union   

Research Activities

Published Papers

• Phase Relation and Reactivity of 1-Hexene under High-Pressure and High-Temperature Conditions

  Ayako Shinozaki, Jun Kawano, Takaya Nagai

  The Journal of Physical Chemistry C 1932-7447 2024/03/29
• Mineral Components of Scleractinian Coral Skeletons Cultured Without Symbionts

  S. Motai, J. Kawano, S. Harii, Y. Seto, T. Watanabe, T. Nagai

  JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES 127 (2) 2169-8953 2022/02 [Refereed]
   

  Skeletons of contemporary reef-building scleractinian corals are formed of aragonite, a polymorph of the calcium carbonate (CaCO3), notwithstanding calcite being a more stable phase under the condition of coral habitats. Circumstances developing aragonite in coral calcification have been addressed currently. Considering that the symbiotic relationship between the coral host and dinoflagellate algae (zooxanthellae) is perhaps relevant to coral calcification, we studied the impact of these symbiotic relationships on CaCO3 polymorph selection. Juvenile scleractinian corals (Acropora tenuis and Acropora digitifera) absent symbionts were cultured in seawaters with varied Mg/Ca molar ratios (mMg/Ca), and the mineral phases of the skeletons were detected employing X-ray diffraction. The findings revealed that diminutive quantities of calcite precipitated as coral skeleton in Acropora digitifera surprisingly in pseudo-present seawater (mMg/Ca similar to 5). Additionally, coral developed skeletons from only calcite in seawater with an mMg/Ca < 1. The evidence gathered in this investigation suggests that the symbiotic relationship affects the establishment of aragonite skeletons in the course of coral calcification.
• Pressure-induced irreversible amorphization of naphthalene and nitrogen-containing heteroaromatic compounds at room temperature

  Ayako Shinozaki, Takaya Nagai, Hiroyuki Kagi, Satoshi Nakano

  Chemical Physics Letters 739 0009-2614 2019/11 [Refereed][Not invited]
   

  Pressure-induced irreversible chemical reactions of naphthalene, 2,3-naphthyridine (2,3-Nap), and 1,5-naphthyridine (1,5-Nap) were observed after compression (> 16-18 GPa) at room temperature. Regardless of the initial materials, amorphous products in which sp(3) carbon was formed were obtained after the samples were recovered at ambient pressure. The X-ray photoelectron spectroscopy (XPS) of the product from naphthalene indicated that the carbon sp(3)/sp(2) ratio was much lower than that of benzene nanothreads. Nitrogen remained in the amorphous products from 1,5-Nap and 2,3-Nap and bonded to both sp(3) and sp(2) carbons.
• Direct Two-Dimensional Time Series Observation of pH Distribution around Dissolving Calcium Carbonate Crystals in Aqueous Solution

  Kawano Jun, Toyofuku Takashi, Nishimura Kaede, Ueda Akiyuki, Nagai Yukiko, Kawada Sachiko, Teng Henry, Nagai Takaya

  CRYSTAL GROWTH & DESIGN 19 (8) 4212 - 4217 1528-7483 2019/08 [Refereed][Not invited]
   

  Copyright © 2019 American Chemical Society. Monitoring in situ local pH changes to dissolving/growing crystal surfaces is critical to decipher the related mechanisms. To date, however, reliable techniques to acquire such measurements remain under-developed. Here we report the first successful attempt to observe time-resolved, two-dimensional distribution of pH around crystals dissolving in aqueous solutions. The local pH change around dissolving calcium carbonate polymorphs (calcite and aragonite) was visualized by using the fluorescent probe 8-hydroxypyrene-1,3,6-trisul-fonic acid HPTS under an optical microscope. The observations unambiguously showed that pH increased and saturated rapidly immediately adjacent to the reactive surfaces on the cleavage rhombs of calcite. Approximately 1 mm away, however, the increase slowed down significantly, generating a steep pH gradient at the crystal-water interface. Aragonite, which has rough fractured surfaces in contrast to the well cleaved calcite, dissolved much faster and showed a stronger tendency for the pH profile to trace the outer shape of crystal grains. These results indicate that this technique is sensitive enough to detect small differences in dissolution between polymorphs and surface conditions and may be used as an effective tool to visualize and understand various reactions in aqueous solutions including environmental weathering and material erosion. ©
• Transformation process of amorphous magnesium carbonate in aqueous solution

  Tanaka Jun-ya, Kawano Jun, Nagai Takaya, Teng Henry

  JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES 114 (2) 105 - 109 1345-6296 2019/04 [Refereed][Not invited]
   

  Amorphous magnesium carbonate (AMC) is an important phase in the early formation stage of magnesium carbonate. In this study, precipitation experiments were conducted to clarify the formation and transformation process of AMC in aqueous solution. Fine AMC particles precipitated, immediately after mixing of Na2CO3 and MgCl2 solutions. Chemical composition of the AMC was determined to be approximately MgCO3 center dot 2H(2)O although two hydration states were expected to exist for AMCs. Subsequently, the AMC transformed in aqueous solutions into needle-like crystals of nesquehonite (MgCO3 center dot 3H(2)O), eventually to tiny polycrystalline particles of dypingite [Mg-5(CO3)(4)(OH)(2)center dot 5H(2)O] via a solvent-mediated processes.
• Structural variations accompanied by thermal expansion of diaspore: in-situ single-crystal and powder X-ray diffraction study

  Teruki Sugiura, Hiroshi Arima, Takaya Nagai, Kazumasa Sugiyama

  PHYSICS AND CHEMISTRY OF MINERALS 45 (10) 1003 - 1010 0342-1791 2018/11 [Refereed][Not invited]
   

  In-situ single-crystal and powder X-ray diffraction (XRD) experiments were performed on diaspore at high temperatures. The powder XRD experiments showed that the dehydration reaction from diaspore to corundum occurs between 703 and 733K. The in-situ single-crystal XRD measurements of diaspore could successfully determine the cell parameters, fractional atomic coordinates and anisotropic displacement parameters at high temperatures, i.e., from 295 to 698K. Temperature variations in the cell parameters indicate that thermal expansion of the alpha-axis is a little higher than those of the b-axis and the c-axis. However, the axial thermal expansivity is not as anisotropic as was previously suggested. The results of structure refinements indicate that such lattice expansion behavior is the result of thermal expansion of the tunnels through O2-H center dot center dot center dot O1 hydrogen-bond separation in the diaspore structure. To the best of our knowledge, this is the first time that the thermal expansion of diaspore has been investigated at an atomic level by in-situ single-crystal XRD experiments at high temperatures.
• Direct observation of symmetrization of hydrogen bond in delta-AlOOH under mantle conditions using neutron diffraction

  Sano-Furukawa Asami, Hattori Takanori, Komatsu Kazuki, Kagi Hiroyuki, Nagai Takaya, Molaison Jamie J, dos Santos, Antonio M, Tulk Christopher A

  SCIENTIFIC REPORTS 8 (1) 2045-2322 2018/10/19 [Refereed][Not invited]
   

  At ambient pressure, the hydrogen bond in materials such as ice, hydrates, and hydrous minerals that compose the Earth and icy planets generally takes an asymmetric O-H center dot center dot center dot O configuration. Pressure significantly affects this configuration, and it is predicted to become symmetric, such that the hydrogen is centered between the two oxygen atoms at high pressure. Changes of physical properties of minerals relevant to this symmetrization have been found; however, the atomic configuration around this symmetrization has remained elusive so far. Here we observed the pressure response of the hydrogen bonds in the aluminous hydrous minerals delta-AlOOH and delta-AlOOD by means of a neutron diffraction experiment. We find that the transition from P2(1)nm to Pnnm at 9.0 GPa, accompanied by a change in the axial ratios of delta-AlOOH, corresponds to the disorder of hydrogen bond between two equivalent sites across the center of the O center dot center dot center dot O line. Symmetrization of the hydrogen bond is observed at 18.1 GPa, which is considerably higher than the disorder pressure. Moreover, there is a significant isotope effect on hydrogen bond geometry and transition pressure. This study indicates that disorder of the hydrogen bond as a precursor of symmetrization may also play an important role in determining the physical properties of minerals such as bulk modulus and seismic wave velocities in the Earth's mantle.
• Dehydroxylation Kinetics of Clay Minerals and Its Application to Friction Heating Along an Imbricate Thrust in an Accretionary Prism

  Hirokazu Masumoto, Jun Kameda, Hiroshi Arima, Kazumasa Sugiyama, Takaya Nagai, Yuzuru Yamamoto

  GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 19 (9) 2991 - 3003 1525-2027 2018/09 [Refereed][Not invited]
   

  Dehydroxylation of clay minerals within fault gouges is significant for assessing transient thermogenesis due to high-velocity, frictional slip along fault zones. The clay minerals kaolinite and chlorite are common in fault zones hosted in sedimentary rocks at subduction margins. To better understand the dehydroxylation processes of these clay minerals, high-temperature X-ray diffraction analyses were carried out by using a 1:1 mixture of kaolinite and chlorite standard samples. We evaluated the kinetic parameters of each dehydroxylation reaction by thermogravimetric analysis using the Friedman method. For kaolinite, the thermogravimetric data are fitted with a one and a half order equation (F-3/2) with an activation energy of 171 kJ/mol and a frequency factor of 5.6 x 10(8) s(-1). The data for chlorite are analyzed by the geometrical contracting model equation (R-2) with an activation energy of 197 kJ/mol and a frequency factor of 4.5 x 10(9) s(-1). Thermal models of frictional heating employing this calibration show that the frictional heating can explain the reported clay mineralogy in a fossil imbricate thrust from a shallow part in an ancient accretionary prism (Shirako Fault, Japan). This result supports the previous assertion, and the observed temperature anomaly appears to demonstrate the frictional heating caused by coseismic slip on this fault.
• Precipitation of halite during calcification of the massive reef-building coral Porites lobata

  Satoko Motai, Jun Kawano, Takaya Nagai, Kohki Sowa, Tsuyoshi Watanabe

  EUROPEAN JOURNAL OF MINERALOGY 28 (2) 265 - 271 0935-1221 2016/03 [Refereed][Not invited]
   

  Detailed observations of mineral phases in the skeleton of a massive reef-building coral were performed at nano- to micrometer scales using an analytical transmission electron microscope. The most notable result is the discovery of a nanosized halite (NaCl) phase coexisting with aragonite (CaCO3) in the coral skeleton. The halite grains are scattered not only along grain boundaries but also inside aragonite grains. The specific relationship of crystallographic orientations and microstructural features between halite and surrounding aragonite suggest that halite precipitated simultaneously with aragonite during calcification. The primary deposition of a mineral phase other than aragonite in a coral skeleton is confirmed for the first time.
• The effect of Mg2+ incorporation on the structure of calcium carbonate clusters: investigation by the anharmonic downward distortion following method

  Jun Kawano, Satoshi Maeda, Takaya Nagai

  PHYSICAL CHEMISTRY CHEMICAL PHYSICS 18 (4) 2690 - 2698 1463-9076 2016/01 [Refereed][Not invited]
   

  Mg2+ is considered to play an important role in the formation of calcium carbonate polymorphs; however, how it affects polymorph selection during the early stages of CaCO3 formation is not yet well understood. In the present study, in order to clarify the effect of Mg2+ on the nucleation of calcium carbonate polymorphs, the stable structures of anhydrous additive-free and Mg-containing calcium carbonate clusters are derived using the anharmonic downward distortion following method, based on quantum chemical calculations. Optimization is performed at the B3LYP/6-31+G(d) level and the solvent effect is induced by the self-consistent reaction field method using the conductor-like polarized continuum calculation model. Calculation results show that incorporating Mg2+ into clusters can change the clusters' stable configuration. In the case of dimers and trimers, a Mg ion strongly prefers to locate at the centre of the clusters, which suggests that Mg is easy to incorporate into the clusters once it is released from its tight hydration shell. Notably, structures similar to the crystalline phase appear when only four CaCO3 units aggregate into the cluster: in the stable structure of the additive-free CaCO3 tetramer, the arrangement of Ca and CO3 ions is almost the same as that of the calcite structure, while the structure of the Mg-containing CaCO3 tetramer resembles the aragonite structure in the way that CO3 ions are stacked. These results indicate that Mg can play a key role in aragonite formation not only by inhibiting calcite growth but also by directly promoting aragonite nucleation in the early stages of CaCO3 formation.
• Incorporation of Mg2+ in surface Ca2+ sites of aragonite: an ab initio study

  Jun Kawano, Hiroshi Sakuma, Takaya Nagai

  PROGRESS IN EARTH AND PLANETARY SCIENCE 2 (Apr) 2:7 (WEB ONLY)  2197-4284 2015/04 [Refereed][Not invited]
   

  First-principles calculations of Mg2+-containing aragonite surfaces are important because Mg2+ can affect the growth of calcium carbonate polymorphs. New calculations that incorporate Mg2+ substitution for Ca2+ in the aragonite {001} and {110} surfaces clarify the stability of Mg2+ near the aragonite surface and the structure of the Mg2+-containing aragonite surface. The results suggest that the Mg2+ substitution energy for Ca2+ at surface sites is lower than that in the bulk structure and that Mg2+ can be easily incorporated into the surface sites; however, when Mg2+ is substituted for Ca2+ in sites deeper than the second Ca2+ layer, the substitution energy approaches the value of the bulk structure. Furthermore, Mg2+ at the aragonite surface has a significant effect on the surface structure. In particular, CO3 groups rotate to achieve six-coordinate geometry when Mg2+ is substituted for Ca2+ in the top layer of the {001} surface or even in the deeper layers of the {110} surface. The rotation may relax the atomic structure around Mg2+ and reduces the substitution energy. The structural rearrangements observed in this study of the aragonite surface induced by Mg2+ likely change the stability of aragonite and affect the polymorph selection of CaCO3.
• Design and performance of high-pressure PLANET beamline at pulsed neutron source at J-PARC

  T. Hattori, A. Sano-Furukawa, H. Arima, K. Komatsu, A. Yamada, Y. Inamura, T. Nakatani, Y. Seto, T. Nagai, W. Utsumi, T. Iitaka, H. Kagi, Y. Katayama, T. Inoue, T. Otomo, K. Suzuya, T. Kamiyama, M. Arai, T. Yagi

  NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 780 55 - 67 0168-9002 2015/04 [Refereed][Not invited]
   

  PLANET is a time (ToF) neutron beamline dedicated to high-pressure and high temperature experiments. The large six axis multi anvil high-pressure press designed for ToF neutron diffraction experiments enables routine data collection at high pressures and high temperatures up to 10 GPa and 2000 K, respectively. To obtain clean data, the beamline is equipped with the incident slits and receiving collimators to eliminate parasitic scattering from the high-pressure cell assembly. The high performance of the diffractometer for the resolution (Delta d/d similar to 0.6%) and the accessible d-spacing range (0.2-8.4 angstrom) together with low parasitic scattering characteristics enables precise structure determination of crystals and liquids under high pressure and temperature conditions. (C) 2015 Elsevier B.V. All rights reserved.
• Superior solid solubility of MnSiO3 in CaSiO3 perovskite

  Lin Li, Takaya Nagai, Yusuke Seto, Kiyoshi Fujino, Jun Kawano, Shoich Itoh

  PHYSICS AND CHEMISTRY OF MINERALS 42 (2) 123 - 129 0342-1791 2015/02 [Refereed][Not invited]
   

  The silicate perovskite phase relation between CaSiO3 and MnSiO3 was investigated at 35-52 GPa and at 1,800 K using laser-heated diamond anvil cells combined with angle-dispersive synchrotron X-ray diffraction and energy-dispersive X-ray spectroscopic chemical analyses with scanning or transmission electron microscopy. We found that MnSiO3 can be incorporated into CaSiO3 perovskite up to 55, and 20 mol % of CaSiO3 is soluble in MnSiO3 perovskite. The range of 55-80 mol % of MnSiO3 in the CaSiO3-MnSiO3 perovskite system could be immiscible. We also observed that the two perovskite structured phases of the Mn-bearing CaSiO3 and the Ca-bearing MnSiO3 coexisted at these conditions. The Mn-bearing CaSiO3 perovskite has non-cubic symmetry and the Ca-bearing MnSiO3 perovskite has an orthorhombic structure with space group Pbnm. All the perovskite structured phases in the CaSiO3-MnSiO3 system convert to the amorphous phase during pressure release. MnSiO3 is the first chemical component confirmed to show such a superior solid solubility in CaSiO3 perovskite.
• 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 0022-4596 2014/10 [Refereed][Not invited]
   

  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. (C) 2014 Elsevier Inc. All rights reserved.
• Formation of a solid solution in the MgSiO3-MnSiO3 perovskite system

  Lin Li, Takaya Nagai, Tomoki Ishido, Satoko Motai, Kiyoshi Fujino, Shoichi Itoh

  PHYSICS AND CHEMISTRY OF MINERALS 41 (6) 431 - 437 0342-1791 2014/06 [Refereed][Not invited]
   

  Experiments using laser-heated diamond anvil cells combined with synchrotron X-ray diffraction and SEM-EDS chemical analyses have confirmed the existence of a complete solid solution in the MgSiO3-MnSiO3 perovskite system at high pressure and high temperature. The (Mg, Mn)SiO3 perovskite produced is orthorhombic, and a linear relationship between the unit cell parameters of this perovskite and the proportion of MnSiO3 components incorporated seems to obey Vegard's rule at about 50 GPa. The orthorhombic distortion, judged from the axial ratios of a/b and monotonically decreases from MgSiO3 to MnSiO3 perovskite at about 50 GPa. The orthorhombic distortion in (Mg-0.5, Mn-0.5)SiO3 perovskite is almost unchanged with increasing pressure from 30 to 50 GPa. On the other hand, that distortion in (Mg-0.9, Mn-0.1)SiO3 perovskite increases with pressure. (Mg, Mn)SiO3 perovskite incorporating less than 10 mol% of MnSiO3 component is quenchable. A value of the bulk modulus of 256(2) GPa with a fixed first pressure derivative of four is obtained for (Mg-0.9, Mn-0.1)SiO3. MnSiO3 is the first chemical component confirmed to form a complete solid solution with MgSiO3 perovskite at the P-T conditions present in the lower mantle.
• Spin transition, substitution, and partitioning of iron in lower mantle minerals

  Kiyoshi Fujino, Daisuke Nishio-Hamane, Takaya Nagai, Yusuke Seto, Yasuhiro Kuwayama, Matthew Whitaker, Hiroaki Ohfuji, Toru Shinmei, Tetsuo Irifune

  PHYSICS OF THE EARTH AND PLANETARY INTERIORS 228 186 - 191 0031-9201 2014/03 [Refereed][Not invited]
   

  Spin transition and substitution of Fe3+ in Fe3+AlO3-bearing MgSiO3 perovskite (Pv) and post-perovskite (PPv) were examined up to 200 and 165 GPa, respectively, at room temperature by X-ray emission spectroscopy (XES) and XRD. The results of XES and XRD indicate that in Pv high spin (HS) Fe3+ at the dodecahedral (A) site replaces Al at the octahedral (B) site and becomes low spin (LS) between 50 and 70 GPa with pressure, while in PPv LS Fe3+ occupies the B-site and Al occupies the A-site above 80-100 GPa. The Fe3+ Al coupled substitution seems to be at work in both Pv and PPv. Combining these results on Fe3+ with the recent first-principles calculations on Fe2+ in Pv and PPv, the spin transition and substitution of iron in pyrolitic lower mantle minerals are proposed. Further, their effects on iron-partitioning among the lower mantle minerals are discussed. (C) 2013 Elsevier B.V. All rights reserved.
• Needle-like grains across growth lines in the coral skeleton of Porites lobata.

  Satoko Motai, Takaya Nagai, Kohki Sowa, Tsuyoshi Watanabe, Naoya Sakamoto, Hisayoshi Yurimoto, Jun Kawano

  Journal of structural biology 180 (3) 389 - 93 1047-8477 2012/12 [Refereed][Not invited]
   

  The skeletal texture and crystal morphology of the massive reef-building coral Porites lobata were observed from the nano- to micrometer scale using an analytical transmission electron microscope (ATEM). The skeletal texture consists of centers of calcification (COCs) and fiber area. Fiber areas contain bundles of needle-like aragonite crystals that are elongated along the crystallographic c-axis and are several hundred nanometers to one micrometer in width and several micrometers in length. The size distribution of aragonite crystals is relatively homogeneous in the fibers. Growth lines are observed sub-perpendicular to the direction of aragonite growth. These growth lines occur in 1-2 μm intervals and reflect a periodic contrast in the thickness of an ion-spattered sample and pass through the interior of some aragonite crystals. These observations suggest that the medium filled in the calcification space maintains a CaCO₃-supersaturated state during fiber growth and that a physical change occurs periodically during the aragonite crystals of the fiber area.
• Spin transition of ferric iron in Al-bearing Mg-perovskite up to 200 GPa and its implication for the lower mantle

  Kiyoshi Fujino, Daisuke Nishio-Hamane, Yusuke Seto, Nagayoshi Sata, Takaya Nagai, Toru Shinmei, Tetsuo Irifune, Hirofumi Ishii, Nozomu Hiraoka, Yong Q. Cai, Ku-Ding Tsuei

  EARTH AND PLANETARY SCIENCE LETTERS 317 407 - 412 0012-821X 2012/02 [Refereed][Not invited]
   

  There are still large discrepancies among the previous reports on the spin transition of iron in Mg-perovskite (Pv). To alleviate this problem, we examined the spin state of Fe3+ in Mg0.85Fe0.153+Al0.15Si0.85O3 Pv up to 200 GPa by X-ray emission spectroscopy (XES) and X-ray diffraction (XRD). The gradual decrease of the high spin (HS) ratio of Fe3+ by low temperature annealing of the samples above similar to 60 GPa in XES and the change of the trend of unit cell volumes with pressure by annealing at 50-60 GPa in XRD indicate that Fe3+ occupies the A-site and is HS below similar to 50 GPa but above 50-60 GPa it gradually replaces Al at the B-site through cation exchange reaction by annealing and becomes low spin (LS), while Fe3+ remaining at the A-site is HS up to 200 GPa. This means that the spin state of Fe3+ depends on Fe3+ occupancies between the A- and B-sites and these Fe3+ occupancies are strongly controlled by the synthesis condition and annealing temperature of the samples through the cation exchange reaction. The present results combined with the previous reports indicate that in Al-bearing Mg-Pv in the lower mantle Fe2+ occupies the A-site and remains HS for the whole lower mantle, while Fe3+ occupies the A-site and is HS below similar to 50 GPa but above 50-60 GPa it replaces Al at the B-site and becomes LS, on the assumption that spin transition pressure of Fe2+ at the A-site is higher than that of Fe3+ at the same site. (C) 2011 Elsevier B.V. All rights reserved.
• 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 0342-1791 2011/12 [Refereed][Not invited]
   

  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.
• Permanent El Nino during the Pliocene warm period not supported by coral evidence

  Tsuyoshi Watanabe, Atsushi Suzuki, Shoshiro Minobe, Tatsunori Kawashima, Koji Kameo, Kayo Minoshima, Yolanda M. Aguilar, Ryoji Wani, Hodaka Kawahata, Kohki Sowa, Takaya Nagai, Tomoki Kase

  NATURE 471 (7337) 209 - 211 0028-0836 2011/03 [Refereed][Not invited]
   

  The El Nino/Southern Oscillation (ENSO) system during the Pliocene warm period (PWP; 3-5 million years ago) may have existed in a permanent El Nino state with a sharply reduced zonal sea surface temperature (SST) gradient in the equatorial Pacific Ocean(1). This suggests that during the PWP, when global mean temperatures and atmospheric carbon dioxide concentrations were similar to those projected for near-term climate change(2), ENSO variability-and related global climate teleconnections-could have been radically different from that today. Yet, owing to a lack of observational evidence on seasonal and interannual SST variability from crucial low-latitude sites, this fundamental climate characteristic of the PWP remains controversial(1,3-10). Here we show that permanent El Nino conditions did not exist during the PWP. Our spectral analysis of the delta(18)O SST and salinity proxy, extracted from two 35-year, monthly resolved PWP Porites corals in the Philippines, reveals variability that is similar to present ENSO variation. Although our fossil corals cannot be directly compared with modern ENSO records, two lines of evidence suggest that Philippine corals are appropriate ENSO proxies. First, delta(18)O anomalies from a nearby live Porites coral are correlated with modern records of ENSO variability. Second, negative-delta(18)O events in the fossil corals closely resemble the decreases in delta(18)O seen in the live coral during El Nino events. Prior research advocating a permanent El Nino state may have been limited by the coarse resolution of many SST proxies, whereas our coral-based analysis identifies climate variability at the temporal scale required to resolve ENSO structure firmly.
• Mechanism of Solid Solution and Crystal Chemistry in MgSiO3-FeAlO3 Perovskite

  NAGAI TAKAYA, HAMANE DAISUKE, FUJINO KIYOSHI

  日本結晶学会誌 The Crystallographic Society of Japan 53 (1) 8 - 12 0369-4585 2011/02 [Refereed][Not invited]
   

  MgSiO₃ dominant perovskite is believed to be the most abundant constituent mineral in the Earth's lower mantle. Generally minerals form solid solutions and their nature should affect on physical properties of minerals. In this paper, we will introduce our recent studies about incorporation mechanism of FeAlO₃ component into MgSiO₃ perovskite and its crystal chemistry.
• 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 2053-2733 2011
• Pressure-induced amorphization of albitic plagioclase in an externally heated diamond anvil cell

  Naotaka Tomioka, Hitomi Kondo, Atsushi Kunikata, Takaya Nagai

  GEOPHYSICAL RESEARCH LETTERS 37 (21) L21301  0094-8276 2010/11 [Refereed][Not invited]
   

  High-pressure and high-temperature experiments of albitic plagioclase up to 41 GPa and 270 degrees C were carried out using an externally heated diamond anvil cell. Raman spectroscopy and transmission electron microscopy of the recovered samples revealed that the amorphization of albite was complete at similar to 37 GPa and room temperature. The amorphization pressure at 170 degrees C was nearly the same as that at room temperature. In contrast, the pressure largely decreased to similar to 31 GPa at 270 degrees C. In comparison with the amorphization pressure of albite in laboratory shock experiments, that in the present static compression experiments is significantly lower (>10 GPa) even at room temperature. This suggests that shorter pressure duration results in a lower degree of amorphization of plagioclase. The formation of maskelynite in shocked meteorites does not necessarily require the very high shock pressure (30-90 GPa) that was previously estimated on the basis of shock recovery experiments. Citation: Tomioka, N., H. Kondo, A. Kunikata, and T. Nagai (2010), Pressure-induced amorphization of albitic plagioclase in an externally heated diamond anvil cell, Geophys. Res. Lett., 37, L21301, doi:10.1029/2010GL044221.
• Synchrotron X-ray diffraction study for crystal structure of solid carbon dioxide CO2-V

  Seto Y, Nishio-Hamane D, Nagai T, Sata N, Fujino K

  INTERNATIONAL CONFERENCE ON HIGH PRESSURE SCIENCE AND TECHNOLOGY, JOINT AIRAPT-22 AND HPCJ-50 215 1742-6588 2010 [Refereed][Not invited]
  
• Development of a software suite on X-ray diffraction experiments

  Yusuke Seto, Daisuke Nishio-Hamane, Takaya Nagai, Nagayoshi Sata

  Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 20 (3) 269 - 276 0917-639X 2010 [Refereed][Not invited]
   

  Angle dispersive powder X-ray diffraction experiments using a flat imaging plate (IP) are one of the most popular methods in high-pressure material science. In order to support such experiments, we developed two software, IPAnalyzer and PDIndexer. IPAnalyzer can convert a two-dimensional Debye-ring pattern to one-dimensional (Bragg-Brentano) geometry. IPAnalyzer can also calibrate experimental parameters (wave length, camera length, and so on) automatically. PDIndexer can display the converted pattern(s) and diffraction peaks calculated for any crystals.
• Pressure-induced spin transition in FeCO3-siderite studied by X-ray diffraction measurements

  T. Nagai, T. Ishido, Y. Seto, D. Nishio-Hamane, N. Sata, K. Fujino

  INTERNATIONAL CONFERENCE ON HIGH PRESSURE SCIENCE AND TECHNOLOGY, JOINT AIRAPT-22 AND HPCJ-50 215 -  1742-6588 2010 [Refereed][Not invited]
   

  We have collected synchrotron X-ray diffraction patterns of FeCO3-siderite after or in-situ laser heating at high pressures to 66 GPa. Diffraction peaks of FeCO3 in all diffraction patterns obtained can be indexed as a trigonal cell. However, calculated cell volumes show an abrupt decrease (about 6.5%) between 47 and 50 GPa at room temperature. This abrupt change of the cell volume on FeCO3 is possibly due to a pressure-induced spin transition of ferrous Fe (HS: high-spin -> LS: low-spin). Because cell parameters obtained at high temperature and at pressures above 50 GPa suggest HS state rather than LS state, the Clapeyron slope of the HS-to-LS transition of FeCO3 should be positive.
• Stability of the perovskite structure and possibility of the transition to the post-perovskite structure in CaSiO3, FeSiO3, MnSiO3 and CoSiO3

  Kiyoshi Fujino, Daisuke Nishio-Hamane, Keisuke Suzuki, Hiroyuki Izumi, Yusuke Seto, Takaya Nagai

  PHYSICS OF THE EARTH AND PLANETARY INTERIORS 177 (3-4) 147 - 151 0031-9201 2009/12 [Refereed][Not invited]
   

  High pressure and high temperature experiments on CaSiO3, FeSiO3, MnSiO3 and CoSiO3 using a laser-heated diamond anvil cell combined with synchrotron X-ray diffraction were conducted to explore the perovskite structure of these compounds and the transition to the post-perovskite structure. The experimental results revealed that MnSiO3 has a perovskite structure from relatively low pressure (ca. 20 GPa) similarly to CaSiO3, while the stable forms of FeSiO3 and CoSiO3 are mixtures of mono-oxide (NaCl structure) + high pressure polymorph of SiO2 even at very high pressure and temperature (149 GPa and 1800 K for FeSiO3 and 79 GPa and 2000 K for CoSiO3). This strongly suggests that the crystal field stabilization energy (CFSE) of Fe2+ with six 3d electrons and Co2+ with seven 3d electrons at the octahedral site of mono-oxides favors a mixture of mono-oxide + SiO2 over perovskite where Fe2+ and Co2+ would occupy the distorted dodecahedral sites having a smaller CFSE (Mn2+ has five 3d electrons and has no CFSE). The structural characteristics that the orthorhombic distortion of MnSiO3 perovskite decreases with pressure and the tolerance factor of CaSiO3 perovskite (0.99) is far from the orthorhombic range suggest that both MnSiO3 and CaSiO3 perovskites will not transform to the CalrO(3)-type post-perovskite structure even at the Earth's core-mantle boundary conditions, although CaSiO3 perovskite has a potentiality to transform to the CalrO(3)-type post-perovskite structure at still higher pressure as long as another type of transformation does not occur. (C) 2009 Elsevier B.V. All rights reserved.
• Change in compressibility of delta-AlOOH and delta-AlOOD at high pressure: A study of isotope effect and hydrogen-bond symmetrization

  Asami Sano-Furukawa, Hiroyuki Kagi, Takaya Nagai, Satoshi Nakano, Satoshi Fukura, Daichi Ushijima, Riko Iizuka, Eiji Ohtani, Takehiko Yagi

  AMERICAN MINERALOGIST 94 (8-9) 1255 - 1261 0003-004X 2009/08 [Refereed][Not invited]
   

  The compression behaviors of delta-AlOOH and delta-AlOOD were investigated under quasi-hydrostatic conditions at pressures Lip 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 delta-AlOOD, which define the plane in which the hydrogen bond lies, are longer than those of delta-AOOH. Under increasing pressure, the a and b axes of delta-AlOOH stiffen at 10 GPa, although the c axis shows no marked change. Identical behavior was found in delta-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 delta-AlOOH and >12 GPa in delta-AlOOD. At these pressures, the pressure dependence of a/b also changes from increasing to decreasing. The unit-cell volumes of delta-AlOOH and delta-AlOOD become slightly less compressible at high pressures. Assuming K(0)(') = 4, the calculated bulk moduli of delta-AlOOH below and above 10 GPa are 152(2) and 219(3) GPa, respectively. Those of delta-AlOOD below and above 12 GPa are 151(1) and 207(2) GPa, respectively.
• Neutron powder diffraction under high pressure at J-PARC

  Wataru Utsumi, Hiroyuki Kagi, Kazuki Komatsu, Hiroshi Arima, Takaya Nagai, Takuo Okuchi, Takashi Kamiyama, Yoshiya Uwatoko, Kazuyuki Matsubayashi, Takehiko Yagi

  NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 600 (1) 50 - 52 0168-9002 2009/02 [Refereed][Not invited]
   

  It is expected that high-pressure material science and the investigation of the Earth's interior will progress greatly using the high-flux pulse neutrons of J-PARC. In this article, we introduce our plans for in situ neutron powder diffraction experiments under high pressure at J-PARC. The use of three different types of high-pressure devices is planned; a Paris-Edinburgh cell, a new opposed-anvil cell with a nano-polycrystalline diamond, and a cubic anvil high-pressure apparatus. These devices will be brought to the neutron powder diffraction beamlines to conduct a "day-one" high-pressure experiment. For the next stage of research, we propose construction of a dedicated beamline for high-pressure material science. Its conceptual designs are also introduced here. (C) 2008 Elsevier B.V. All rights reserved.
• Introduction of the high pressure neutron diffraction projects in J-PARC

  Takaya Nagai, Hiroshi Arima, Takuo Okuchi, Hiroyuki Kagi, Takehiko Yagi

  Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 19 (1) 15 - 23 0917-639X 2009 [Refereed][Not invited]
   

  It is great exciting news for our high pressure science community in Japan that the first pulsed neutron beams were delivered to J-PARC Materials & Life Science Experimental Facility (MLF) on May 30th, 2008. We believe that the newly dedicated pulsed neutron beams will open a new window in the high-pressure science world. Over the past 7 years, we have prepared some projects to build a high pressure and high temperature material science beamline in the MLF. In this article, we will give a brief overview of the progress of those projects and also introduce a newly designed high-pressure cell and a neutron focusing mirror for in-situ neutron diffraction experiments at high pressure and high temrjerature.
• Fate of carbonates within oceanic plates subducted to the lower mantle, and a possible mechanism of diamond formation

  Yusuke Seto, Daisuke Hamane, Takaya Nagai, Kiyoshi Fujino

  PHYSICS AND CHEMISTRY OF MINERALS 35 (4) 223 - 229 0342-1791 2008/05 [Refereed][Not invited]
   

  We report on high-pressure and high-temperature experiments involving carbonates and silicates at 30-80 GPa and 1,600-3,200 K, corresponding to depths within the Earth of approximately 800-2,200 km. The experiments are intended to represent the decomposition process of carbonates contained within oceanic plates subducted into the lower mantle. In basaltic composition, CaCO3 (calcite and aragonite), the major carbonate phase in marine sediments, is altered into MgCO3 (magnesite) via reactions with Mg-bearing silicates under conditions that are 200-300C colder than the mantle geotherm. With increasing temperature and pressure, the magnesite decomposes into an assemblage of CO2 + perovskite via reactions with SiO2. Magnesite is not the only host phase for subducted carbon-solid CO2 also carries carbon in the lower mantle. Furthermore, CO2 itself breaks down to diamond and oxygen under geotherm conditions over 70 GPa, which might imply a possible mechanism for diamond formation in the lower mantle.
• High-pressure phase relation of MnSiO3 up to 85 GPa: Existence of MnSiO3 perovskite

  Kiyoshi Fujino, Keisuke Suzuki, Daisuke Hamane, Yusuke Seto, Takaya Nagai, Nagayoshi Sata

  AMERICAN MINERALOGIST 93 (4) 653 - 657 0003-004X 2008/04 [Refereed][Not invited]
   

  The high-pressure phase relation of MnSiO3 was examined up to 85 GPa and 2600 K using a laser-heateddiamond-anvil cell combined with synchrotron radiation. MnSiO3 garnet decomposes into a mixture of MnO with a rock-salt structure (B1) + SiO2 stishovite at pressures higher than similar to 20 GPa and temperatures higher than similar to 1200 K. However, MnO (B1) + SiO2 stishovite further transforms to a perovskite structure with increasing pressure. The phase boundary between these structures is positive in the pressure-temperature diagram. The triple point of garnet, MnO + SiO2 and perovskite in the pressure-temperature diagram is similar to 20 CiPa and 1200 K. MnSiO3 perovskite is orthorhombic, and consistent with space group Pbnm, both at high pressure and high temperature and at high pressure and room temperature, but becomes amorphous during decompression. The refined cell parameters of MnSiO3 perovskite at 85 GPa and 2600 K are a = 4.616(2) angstrom, b = 4.653(2) angstrom, c = 6.574(3) angstrom, and V = 141.2(2) angstrom(3). The a/b ratio increases (approaches 1) with pressure and temperature, while the root 2a/c ratio remains nearly constant (<1). This indicates that the orthorhombic distortion decreases and the structure tends toward a tetragonal perovskite with increasing pressure and temperature.
• Effect of FeAlO3 incorporation into MgSiO3 on the bulk modulus of perovskite

  NISHIO-HAMANE DAISUKE, SETO YUSUKE, FUJINO KIYOSHI, NAGAI TAKAYA

  Phys Earth Planet Interiors 166 (3-4) 219 - 225 0031-9201 2008/02 [Refereed][Not invited]
   

  The effect of FeAlO3 incorporation into MgSiO3 On the bulk modulus of perovskite has been investigated in Mg0.85Fe0.15Al0.15Si0.85O3 on the basis of high-pressure and high-temperature in-situ X-ray diffraction measurements in a laser-heated diamond anvil cell. The Birch-Murnaghan equation of state (K-0' = 4) yields zero-pressure bulk moduli of 252(1) GPa and 259(1) GPa for Mg0.85Fe0.15Al0.15Si0.85O3 perovskite and MgSiO3 perovskite, respectively, using Tsuchiya's pressure scale. The effect of the FeAlO3 is a decrease in the bulk modulus. This effect is not explained by the compression mechanism of the oxygen vacancy or partial amorphisation. Rather, the decrease of the bulk modulus may be associated with high-pressure behavior of the perovskite structure that is distorted by the coupled substitution of Mg + Si = Fe + Al. Mg0.85Fe0.15Al0.15Si0.85O3 perovskite was also found to be stable up to 143 GPa and 2500 K based on Tsuchiya's pressure scale. The other effect of the addition of FeAlO3 is an expansion of the perovskite stability field towards higher pressures. There may be an empirical relation between the bulk modulus decrease and the post-perovskite transition pressure increase on incorporation of trivalent cations into perovskite by mechanisms other than the oxygen vacancy compression. (C) 2008 Elsevier B.V. All rights reserved.
• What Kind of Information in Mineralogy can be Expected by a New Intense Pulsed Neutron Source?

  NAGAI TAKAYA, INOUE TOORU, YAGI TAKEHIKO

  日本結晶学会誌 The Crystallographic Society of Japan 50 (1) 109 - 113 0369-4585 2008/02 [Refereed][Not invited]
   

  It is great pleasure that the first pulsed neutron beam will be delivered to Materials and Life Science Facility in J-PARC on May, 2008. In the last quarter of a century, synchrotron radiation has opened new scientific windows of mineralogy, especially a field of mineral physics at high pressure. In the next several 10 years, we believe that the newly dedicated pulsed neutron source facility in J-PARC will provide us many opportunities to explore the next new world of mineralogy. In this paper we will give a brief overview of mineral sciences by neutron scattering and introduce our research project about the water-mineral interaction in the Earth by using the pulsed neutron source.
• 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 0895-7959 2008 [Refereed][Not invited]
   

  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 20 GPa. Furthermore, hydrostaticity was much better than conventional pressure-transmitting media used for infrared spectroscopy. Infrared absorption spectra of alpha-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.
• Comparative Raman spectroscopic study on ilmenite-type MgSiO3 (akimotoite), MgGeO3, and MgTiO3 (geikielite) at high temperatures and high pressures

  Taku Okada, Toshiharu Narita, Takaya Nagai, Takamitsu Yamanaka

  AMERICAN MINERALOGIST 93 (1) 39 - 47 0003-004X 2008/01 [Refereed][Not invited]
   

  The Raman spectra Of MgXO3-ilmenites (X = Si, Ge, Ti) were recorded up to 773 K at ambient pressure and up to 20-30 GPa at room temperature. Temperature and pressure dependence of the force constant of X-O stretching bands revealed that the expansion and compression behavior of XO6 octahedra differed in the three ilmenites. For SiO6 and GeO6 octahedra, the shorter Si-O or Ge-O bonds became more lengthened with temperature and more shortened with pressure than did the longer Si-O or Ge-O bonds. In contrast, for TiO6 octahedra, the longer Ti-O bonds became more lengthened with temperature and more shortened with pressure than did the shorter Ti-O bonds. For SiO6 and GeO6 at high temperatures and TiO6 at high pressures, the cation positions moved in the direction of the c axis and tended to approach the center of the octahedra, decreasing the distortion Of XO6. For SiO6 and GeO6 at high pressures and TiO6 at high temperatures, the cations moved away from the center, increasing the distortion of XO6. One of the anharmonic correction terms on isochoric specific heat was also elucidated. The anharmonic effects were related to the elastic Debye temperature of the three ilmenites.
• Urric iron and aluminum partitioning between MgSiO3- and CaSiO3-perovskites under oxidizing conditions

  Daisuke Nishio-Hamane, Yusuke Seto, Takaya Nagai, Kiyoshi Fujino

  JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES 102 (5) 291 - 297 1345-6296 2007/10 [Refereed][Not invited]
   

  Ferric iron and aluminum partitioning between MgSiO3-dominant perovskite (Mg-Pv) and CaSiO3-dominant perovskite (Ca-Pv) was investigated at 27-100 GPa and 1600-2500 K under oxidizing conditions using a starting composition of 0.85CaMgSi(2)O(6) + 0.15Fe(3+)AlO(3) employing a combined laser-heated diamond anvil cell, synchrotron radiation, and analytical transmission electron microscopy. The product phases were Mg-Pv, Ca-Pv, and a small amount of stishovite at pressures below 30 GPa, while a two-phase assemblage of Mg-Pv and Ca-Pv was identified at pressures above 30 GPa. The appearance of stishovite below 30 GPa indicates the partial formation of an oxygen-deficient perovskite from 2ASiO(3) + Fe3+AlO3 = 2AFe(0.5)(3+)Al(0.5)O(2.5)(oxygen-deficient perovskite) + 2SiO(2) (stishovite), where A = Mg or Ca. The composition of Mg-Pv and Ca-Pv show that ferric iron and aluminum were predominantly incorporated into Mg-Pv under oxidizing conditions, indicating that Mg-Pv is the dominant host phase for ferric iron and aluminum even under highly oxidizing lower mantle conditions.
• Static amorphization of plagioclase: Comparison to the formation pressure of diaplectic glass in shock experiments

  N. Tomioka, A. Kunikata, H. Kondo, T. Nagai, T. Narita, T. Yamanaka

  METEORITICS & PLANETARY SCIENCE 42 A148 - A148 1086-9379 2007/08 [Refereed][Not invited]
  
• Single-crystal X-ray diffraction study of high-pressure phases of KHCO3

  K. Komatsu, H. Kagi, T. Nagai, T. Kuribayashi, J. B. Parise, Y. Kudoh

  AMERICAN MINERALOGIST 92 (8-9) 1270 - 1275 0003-004X 2007/08 [Refereed][Not invited]
   

  Monoclinic and triclinic high-pressure phases of KHCO3 were identified using in situ high-pressure single-crystal X-ray analysis. These monoclinic and triclinic phases, designated as phases IV and V, respectively, differ from three previously identified phases: I-III. The lattices of the two phases are superimposed along a(IV)(*) = 2 x a(v)(*) and hk0 and h0l nets of both phases lie on the same plane, i.e., the (100) plane is common in both lattices in real space. The space group of phase IV is P2(1),/b11 with lattice constants of a = 10.024(3) angstrom, b = 6.912(5) angstrom, c = 4.1868(11) angstrom, alpha = 115.92(4)degrees, and V = 260.9(2) angstrom(3). The crystal structure of phase IV, excluding the hydrogen atoms, was successfully determined by direct methods and is isostructural with a cesium hydrogen carbonate CSHCO3.
• Effect of the incorporation of FeAlO3 into MgSiO3 perovskite on the post-perovskite transition

  Daisuke Nishio-Hamane, Kiyoshi Fujino, Yusuke Seto, Takaya Nagai

  GEOPHYSICAL RESEARCH LETTERS 34 (12) L12307  0094-8276 2007/06 [Refereed][Not invited]
   

  Effect of the incorporation of FeAlO3 into MgSiO3 perovskite on post-perovskite transition was investigated in Mg0.85Fe0.15Al0.15Si0.85O3 on the basis of high pressure and temperature in-situ X-ray diffraction experiments using a laser heated diamond anvil cell. Results demonstrate that single perovskite is stable up to 143 GPa and 2500 K and perovskite and post-perovskite coexist at 157- 162 GPa and 1600 - 2500 K for the pressure scales by Tsuchiya ( 2003). Post-perovskite formed as single phase at 176 - 178 GPa and 1600 - 2600 K. The post-perovskite transition pressure in Mg0.85Fe0.15Al0.15Si0.85O3 was much higher than that in MgSiO3. The present experimental study indicates that the incorporation of FeAlO3 component expands the stability region of perovskite toward high pressure. The FeAlO3 concentration may strongly influence the thickness of the D '' layer at the lowermost of the lower mantle.
• Ferric iron and aluminum partitioning between MgSiO3- and CaSiO3- perovskites under oxidizing conditions

  Nishio-Hamane D, Seto Y, Nagai T, Fujino K

  Journal of Mineralogical and Petrological Sciences 102 (10) 291 - 297 0342-1791 2007 [Refereed][Not invited]
  
• Decarbonation reaction of magnesite in subducting slabs at the lower mantle

  N. Takafuji, K. Fujino, T. Nagai, Y. Seto, D. Hamane

  PHYSICS AND CHEMISTRY OF MINERALS 33 (10) 651 - 654 0342-1791 2006/12 [Refereed][Not invited]
   

  High-pressure and temperature experiments (28-62 GPa, and 1,490-2,000 K, corresponding to approximately 770-1,500 km depth in the mantle) have been conducted on a MgCO3 + SiO2 mixture using a laser-heated diamond anvil cell combined with analytical transmission electron microscope observation of the product phases to constrain the fate of carbonates carried on the subducting basalt into the lower mantle. At these conditions, the decarbonation reaction MgCO3 (magnesite) + SiO2 (stishovite) -> MgSiO3 (perovskite) + CO2 (solid) has been recognized. This indicates that above reaction takes place as a candidate for decarbonation of the carbonated subducting mid ocean ridge basalts in the Earth's lower mantle.
• The phase transitions of KNbO3 under high pressure

  Y. Nakamoto, K. Ohi, T. Okada, T. Nagai, T. Yamanaka

  FERROELECTRICS 337 1361 - 1367 0015-0193 2006 [Refereed][Not invited]
   

  A ferroelectric KNbO3 has been investigated to 11.4 GPa at room temperature by angle-dispersive powder diffraction with diamond anvil cell using synchrotron radiation, which was performed by a high-resolution evaluation setting. KNbO3 transforms from orthorhombic to tetragonal lattice at around 6 GPa, and further transforms to a cubic lattice at about 9.2 GPa. Single-crystal X-ray diffraction studies under pressures clarified the space groups of the three phases and their lattice constants. The extinction rule of the observed reflections and diffraction intensity distribution proved Cm2m, P4mm and Pm3m for orthorhombic, tetragonal and cubic polymorphs, respectively.
• A new polymorph of FeAlO3 at high pressure

  T Nagai, D Hamane, PS Devi, N Miyajima, T Yagi, T Yamanaka, K Fujino

  JOURNAL OF PHYSICAL CHEMISTRY B 109 (39) 18226 - 18229 1520-6106 2005/10 [Refereed][Not invited]
   

  Synchrotron X-ray diffraction measurements confirmed that a new polymorph of FeAlO3 could be synthesized at about 1800 K and 72 GPa. This phase can be indexed on an orthorhombic cell and transforms into the trigonal form on release of pressure. The cla ratio of about 2.71 of the trigonal phase suggests corundum structure of FeAlO3 rather than LiNbO3 or ilmenite structure. This conclusion also suggests that the high-pressure orthorhombic phase could be the Rh2O3(II) structure rather than the GdFeO3-type perovskite structure.
• Structure change of MgSiO3, MgGeO3, and MgTiO3 ilmenites under compression

  T Yamanaka, Y Komatsu, M Sugahara, T Nagai

  AMERICAN MINERALOGIST 90 (8-9) 1301 - 1307 0003-004X 2005/08 [Refereed][Not invited]
   

  Compression mechanisms of A(2+)B(4+)O(3) ilmenites with compositions MgSiO3 (stable at high pressures), MgGeO3 (stable at moderate pressures), and MgTiO3 (stable at ambient pressure) were investigated at high pressure by single-crystal structure analysis, using both synchrotron radiation and an MoK alpha rotating-anode X-ray generator. The distortions of AO(6) (A:Mg) and BO6 (B: Si, Ge, Ti) octahedra under pressure were parameterized by bond length, shared-face area, site-volume ratio, and A(2+)-B4+ interatomic distance across the shared edges and shared face. The AO(6) octahedral volume is much more compressive than the BO6 octahedral volume. Of the three samples, both the AO(6) and BO6 octahedra are most rigid in MgSiO3. The A(2+)-B4+ interatomic distance becomes more shortened with increasing pressure than do the A(2+)-A(2+) and B4+-B4+ distances. The compression of Mg-Si is more remarkable than that of Mg-Ge and Mg-Ti. The A-B interatomic distance along c is more compressed with increasing pressure than A-A and B-B along a. The short A-B distance across the shared face becomes more shortened than the A-A and B-B distances across the shared edge. The cation position moves in the direction of c with pressure and tends to approach the center of the AO(6) and BO3 octahedra with increasing pressure. The regularity of the octahedra is enhanced at higher pressure. Both quadratic elongation and bond angle variance verify the reduction of the deformation of AO(6) and BO6 octahedra with pressure.
• Fe(3+) and Al solubilities in MgSiO(3) perovskite: implication of the Fe(3+)AlO(3) substitution in MgSiO(3) perovskite at the lower mantle condition

  D Nishio-Hamane, T Nagai, K Fujino, Y Seto, N Takafuji

  GEOPHYSICAL RESEARCH LETTERS 32 (16) L16306.1-L16306.4  0094-8276 2005/08 [Refereed][Not invited]
   

  Perovskite in the starting composition of Mg(3)Fe(3+)AlSi(3)O(12) was investigated at 24 and 51 GPa and 2100 K using a laser-heated diamond anvil cell (LHDAC) and an analytical transmission electron microscopy ( ATEM) to understand the solubilities of Fe(3+) and Al into MgSiO(3)-dominated perovskite. A single phase of orthorhombic perovskite was formed at 51 GPa and 2100 K and the Fe(3+) AlO(3) bearing perovskite showed no structural change during decompression. The samples synthesized at 24 GPa and 2100 K showed minor amounts of magnesioferrite and stishovite phases in spaces along the perovskite grain boundaries. These results indicate that the solubility of ferric iron incorporated as the Fe(3+) AlO(3) component in MgSiO(3)-based perovskite is higher and slightly lower than 25 mole % at 51 and 24 GPa, respectively.
• Pressure response on hydrogen bonds in potassium hydrogen carbonate and sodium hydrogen carbonate

  H. Kagi, T. Nagai, K. Komatsu, T. Okada, C. Wada, J. S. Loveday, J. B. Parise

  Journal of Neutron Research 13 (1-3) 21 - 26 1477-2655 2005 [Refereed][Not invited]
   

  Pressure responses of hydrogen bonding interactions were compared between potassium hydrogen carbonate (KHCO3) and sodium hydrogen carbonate (NaHCO3). KHCO3 undergoes a pressure-induced structural change at 2.8 GPa and room temperature whereas no phase transition has been found so far for NaHCO3 up to 11 GPa. KHCO3 exhibits a substantial decrease in the OZH … O angle with increasing pressure. This change could be a trigger for the phase transition at 2.8 GPa. By contrast, no significant change in OZH … O angle was observed for NaHCO3 up to 7 GPa. Based on the observations using neutron diffraction, X-ray diffraction and vibrational spectroscopy at high pressure, a possible mechanism for the phase transition of KHCO3 is suggested. In addition, the phase boundary of KHCO3 caused by the pressure-induced transition was determined using in situ Raman spectroscopy at high pressure. © 2004 Taylor & Francis Ltd.
• Structure change of Mn2O3 under high pressure and pressure-induced transition

  T Yamanaka, T Nagai, T Okada, T Fukuda

  ZEITSCHRIFT FUR KRISTALLOGRAPHIE 220 (11) 938 - 945 0044-2968 2005 [Refereed][Not invited]
   

  Bixbyite (Mn,Fe)(2)O-3 has a C-type rare-earth oxide structure with space group of Ia (3) over bar and different from corundum structure R (3) over barc. Single-crystal structure analyses and powder diffraction experiments were carried out using synchrotron radiation under high pressures up to 41.21 GPa. Lattice constants and bond distances were elucidated as a function of pressure. Single crystal structure analyses under high pressures up to 9.64 GPa have been executed using DAC. There are two octahedral Mn3+ sites: M1 ((3) over bar) and M2 (.2.). M1O(6) and M2O(6) octahedral volumes and void space of vacant sites show different compression curves. M1O(6) octahedron is less compressive than M2O(6) octahedron. The former is a little deformed from an ideal octahedron with m (3) over barm of MnO6 but the latter is a largely distorted octahedron. The quadratic elongation is applied in order to comprehend the polyhedral distortion and finite homogeneous strain. Both octahedra do not show a noticeable Jahn-Teller distortion induced from Mn3+. Six bond lengths Of M1O(6) are equivalent but the octahedron more elongates along the direction of (3) over bar axis with increasing pressure and is more deformed from the regular octahedron. The M2O(6) octahedron has two long bond distances among six bonds, which are most compressive. The octahedral deformations seem to reduce the Jahn-Teller effect due to the compression. The bulk modulus: Ko = 169.1(4.9) GPa and Ko' = 7.35(0.99), was observed from the volume change with pressure. Pressure-induced phase transition was confirmed at about 21 GPa with a large hysteresis. The transition is reversible and non-quenchable. Powder indexing of the high-pressure phase was carried out using diffraction pattern taken at 35.06 GPa. It has a monoclinic symmetry and is not a corundum, Rh2O3(II) or perovskite structure.
• Raman spectroscopy of cubic boron nitride under high temperature and pressure conditions: A new optical pressure marker

  T Kawamoto, KN Matsukage, T Nagai, K Nishimura, T Mataki, S Ochiai, T Taniguchi

  REVIEW OF SCIENTIFIC INSTRUMENTS 75 (7) 2451 - 2454 0034-6748 2004/07 [Refereed][Not invited]
   

  The pressure dependence of Raman peaks of cubic boron nitride (cBN) is determined at 100, 200 and 300 degreesC using pressure scales of ruby and gold. At pressures lower than 6 GPa, the pressure dependences of cBN Raman determined with the ruby pressure scale for transverse-optical (TO) and longitudinal-optical modes are 3.45+/-0.02 and 3.36+/-0.02 cm(-1) /GPa at 100 degreesC and 3.43+/-0.02 and 3.44+/-0.07 cm(-1)/GPa at 300 degreesC, respectively. These values are consistent with those in a previous study conducted at room temperature using the ruby pressure scale. Synchrotron x-ray diffraction experiments using a gold pressure marker also yield 3.45+/-0.03 cm(-1) /GPa for TO mode at 200 degreesC in a range of pressure up to 32 GPa. Under the present pressure and temperature conditions, the pressure dependence of Raman peaks of cBN seems to be independent of the temperature conditions. cBN can be used as an optical pressure marker under high temperature conditions. (C) 2004 American Institute of Physics.
• Looking into the Deep Earth with Neutron

  Kagi Hiroyuki, Nagai Takaya

  hamon 日本中性子科学会 14 (1) 32 - 34 1349-046X 2004 [Refereed][Not invited]
   

  Water is a key material for the dynamics of the earth such as volcanic eruption and earthquakes. In particular, significant change in the mineral properties induced by the addition of water (hydrogen) is an intriguing research area closely related to behavior of hydrogen bonding at high pressure. Our recent progress on this field and future perspective are reviewed.
• Intense pulsed neutron sources open a new window of mineralogy

  Takaya Nagai, Hiroyuki Kagi

  Japanese Magazine of Mineralogical and Petrological Sciences 33 (2) 62 - 71 1349-7979 2004 [Refereed][Not invited]
   

  Recently mineral scientists have paid attention to the neutron scattering, because some intense pulsed neutron sources have been constructed or in planning in the world. In Japan, the High Energy Accelerator Research Organization (KEK) and the Japan Atomic Energy Research Institute (JAERI) have jointly constructed a 1 MW pulsed neutron source (JSNS) at Tokai, Ibaraki. The neutron and the x-ray diffraction should provide complementary information each other because of their physical properties. For example, light elements like hydrogen are almost invisible for x-ray and it is difficult for x-ray to distinguish neighboring elements in the Periodic Table such as Mg, Al and Si, which are major elements in geological materials and often show interesting order-disorder relating phenomena. However, neutron expects to provide useful information about those invisible problems of x-ray since the scattering cross-section of neutron is independent of the atomic numbers. In this paper, we will give an overview of elastic neutron scattering and give some ideas of mineral physics at high pressure and high temperature. In addition, we will shortly introduce the JSNS and our proposal of a high pressure/temperature material science station in the JSNS. © 2004, Japan Association of Mineralogical Sciences. All rights reserved.
• What kind of science can be targeted by the combination of neutron elastic scattering and high pressure devices?

  Takaya Nagai

  Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 14 (2) 128 - 134 0917-639X 2004 [Refereed][Not invited]
   

  In this article, I tried to discuss what kind of science could be targeted by the combination of neutron elastic scattering and high pressure devices. Construction of a user facility providing intense pulsed neutron is now in progress in Japan Proton Accelerator Research Complex (J-PARC), Tokai, Ibaraki, Japan. Since we are eager to obtain a beam line dedicated for high pressure sciences in the exciting facility, I reviewed what kind of science in the high pressure world has been already performed by neutron elastic scattering technique in order to think about its new application to high pressure sciences.
• Pressure-induced phase transformation of kalicinite (KHCO3) at 2.8 GPa and local structural changes around hydrogen atoms

  H Kagi, T Nagai, JS Loveday, C Wada, JB Parise

  AMERICAN MINERALOGIST 88 (10) 1446 - 1451 0003-004X 2003/10 [Refereed][Not invited]
   

  The pressure-induced structural phase transition in kalicinite, KHCO3, has been studied by neutron powder diffraction, and infrared (IR) and Raman spectroscopy at high pressure and room temperature. The neutron diffraction study of deuterated kalicinite (KDCO3) revealed that for the one site for hydrogen (deuterium) found in the low-pressure phase, the O-D...O angle decreases from 176 to 161degrees and the distance between donor and acceptor 0 atoms of the O-D...O group decreases from 2.66 to 2.59 Angstrom in the pressure range from 0 to 2.5 GPa. The crystal structure of the high-pressure polymorph was not determined. Infrared spectra were obtained at pressures up to 6.3 GPa using a diamond anvil cell. At ambient pressure, the O-H stretching, O-H...O in-plane bending, and O-H...O out-of-plane bending modes occur at 2620, 1405, and 988 cm(-1), respectively. The frequency of the O-H stretch mode was nearly constant in the pressure range from 0 to 2.8 GPa, while that of O-H...O in-plane bending and out-of-plane modes increased with increasing pressure up to 2.8 GPa and remained constant above the phase transition pressure. The Raman spectra showed a clear phase transition at 2.8 GPa. The three Raman modes observed are assigned to internal vibrational modes of HCO3- and this suggests that the surrounding environment did change dramatically at the phase transition. These results suggest that the phase transition in kalicinite is triggered by the distortion of C-O-H bond at high pressure.
• Variation of hydrogen bonded O center dot center dot center dot O distances in goethite at high pressure

  T Nagai, H Kagi, T Yamanaka

  AMERICAN MINERALOGIST 88 (10) 1423 - 1427 0003-004X 2003/10 [Refereed][Not invited]
   

  In-situ synchrotron X-ray powder diffraction experiments on goethite were performed up to 24.5 GPa using a diamond-anvil cell at BL-18C in the Photon Factory, Japan. The compression behavior of goethite is anisotropic: the a axis, which is close to the direction of the hydrogen bond, is almost twice as compressible as the b and c axes. A second-order Birch-Murnaghan fit (K' = 4) to the unit-cell volumes and pressures up to 24 GPa gave a bulk modulus K-0 = 111(2) GPa. The pressure medium apparently affects the compression behavior of goethite, as a sudden strain broadening occurs above I I GPa, where solidification of the 4:1 methanol: ethanol pressure medium occurs. The crystal structure of goethite was refined by means of the Rietveld method at several pressures below 10 GPa. The main compression occurs in the "vacant channels" in the crystal structure, where the O-H...O bridges are located. The hydrogen-bonded O...O distance shortens with increasing pressure at the rate of about -0.023 Angstrom/GPa and reaches 2.60(l) Angstrom at 9 GPa.
• B1-B2 transition in CaO and possibility of CaSiO3-perovskite decomposition under high pressure

  Takamitsu Yamanaka, Kouichi Kittaka, Takaya Nagai

  Journal of Mineralogical and Petrological Sciences 97 (4) 144 - 152 1349-3825 2002 [Refereed][Not invited]
   

  X-ray powder diffraction measurements of CaO at high pressure and temperature have been performed using a lever-spring type diamond anvil cell equipped with an external ring heater. The B1 structure transformed into B2 at about 61.2-63.2GPa at room temperature during the compression, and the back transformation from the B2 to B1 structure was found at 59.8GPa during the depression. The equation of states of both the B1 and B2 structures are obtained by Birch-Murnaghan equation. Because B2 structure of CaO is unstable at ambient conditions, the bulk modulus of the B2 structure at high temperature was firstly determined from the P-V-T curve. The B1-B2 transition pressure slightly lowers from 58.8GPa at 295K to 53.1GPa at 685K, resulting in dP/dT< 0. A back transformation from the B2 to B1 structure by depression shows a large hysteresis. The B1-B2 transition highly depends on pressure rather than temperature. Only from the volumes of the CaSiO3 components, CaSiO3 perovskite possibly decomposes to SiO2 (CaCl2 type) and CaO (B2) in the pressure and temperature range of the lower mantle.
• The first observation of a pressure-induced phase transition and compression behavior of kalicinite (KHCO3) at room temperature

  T Nagai, H Kagi, T Yamanaka

  SOLID STATE COMMUNICATIONS 123 (9) 371 - 374 0038-1098 2002 [Refereed][Not invited]
   

  In situ synchrotron X-ray diffraction measurements were performed on kalicinite (KHCO3) up to 9.0 GPa at room temperature. A reversible phase transition was observed at about 2.8 GPa. The structure of the high-pressure phase has not been identified yet. The compression behavior of kalicinite is highly anisotropic and the a-axis is about two times more compressible than the b- and c-axes. The compression behavior is different from that during contraction in lowering the temperature and this suggests that the hydrogen bonded (OO)-O-... distance is significantly shortened with increasing pressure. (C) 2002 Elsevier Science Ltd. All rights reserved.
• Phase transition of zeolite RHO at high-pressure

  Y Lee, JA Hriljac, T Vogt, JB Parise, MJ Edmondson, PA Anderson, DR Corbin, T Nagai

  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 123 (34) 8418 - 8419 0002-7863 2001/08 [Refereed][Not invited]
  
• Sequential high-pressure transformations of FeGeO3 high-P clinopyroxene (C2/c) at temperatures up to 365 degrees C

  T Hattori, T Tsuchiya, T Nagai, T Yamanaka

  PHYSICS AND CHEMISTRY OF MINERALS 28 (6) 377 - 387 0342-1791 2001/07 [Refereed][Not invited]
   

  In order to elucidate high-pressure transformations of high-P clinopyroxene (C2/c) at kinetically low temperature where atoms are not thermally activated, the transformation processes of FeGeO3 clinopyroxene (C2/c) have been investigated at pressures up to 20 GPa and 365 degreesC by powder X-ray diffraction using a synchrotron radiation source and TEM observation. With increasing pressure up to 20 GPa at room temperature, FeGeO3 high-P clinopyroxene (C2/c) reversibly transforms into a new high-pressure phase, FeGeO3(II). On increasing the temperature up to 365 degreesC, this phase rapidly transforms into FeGeO3 ilmenite within about 2 h. Intensity analysis of the X-ray diffraction pattern reveals that the high-pressure phase of FeGeO3(II) has an intermediate structure between clinopyroxene and ilmenite: the cation arrangement is similar to that of clinopyroxene and the oxygen arrangement is similar to that of ilmenite. The comparison of the crystal structures of these polymorphs suggests that clinopyroxene to FeGeO3(II) and FeGeO3(II) to ilmenite transformations are performed by the slight deformation of the oxygen packing and the short-range movement of cations, respectively. It is shown that this high-P clinopyroxene transforms into ilmenite through a low-activation energy path under the low-temperature condition.
• Pressure dependence of effective pair potentials in AgBr determined by extended X-ray absorption fine structure

  A Yoshiasa, K Murai, T Nagai, Y Katayama

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 40 (4A) 2395 - 2398 0021-4922 2001/04 [Refereed][Not invited]
   

  The pressure dependence of extended X-ray absorption fine structure (EXAFS) Debye-Waller factors in AgBr has been investigated using the cumulant expansion method. The Br K-edge EXAFS spectra were measured in the transmission mode under high pressure (less than or equal to9.1 GPa) at room temperature using a cubic anvil type apparatus (MAX90) and synchrotron radiation from the Photon Factory, Tsukuba. The effective pair potentials, V(u) = au(2)/2 + bu(3)/3!!, were evaluated and the potential coefficient a at 2.1, 4.2 and 6.1 GPa are 1.59(4), 1.75(4) and 1.91(4) eV/Angstrom (-2), respectively. The energies of the third-order anharmonic potential coefficient b maintain nearly constant values with pressure though the third-order cumulant sigma (3) decreases with increasing in pressure.
• 「放射光を使ってみませんか」 放射光利用ハンドブック 放射光を用いたX線回折法による高圧下における結晶構造の精密決定

  服部高典, 福田智男, 橘高弘一, 永井隆哉, 山中高光

  岩石鉱物科学 日本鉱物科学会 30 (2) 98 - 99 1345-630X 2001/03 [Refereed][Not invited]
  
• Single-crystal X-ray diffraction study of FeGeO3 high-P clinopyroxene (C2/c) up to 8.2 GPa

  T Hattori, T Nagai, T Yamanaka, S Werner, H Schulz

  AMERICAN MINERALOGIST 85 (10) 1485 - 1491 0003-004X 2000/10 [Not refereed][Not invited]
   

  To elucidate pressure effects on the crystal structure of the high-P clinopyroxene (space group C2/c), the compression process of FeGeO3 clinopyroxene (C2/c) was investigated up to 8.2 GPa by single-crystal X-ray diffraction. The crystal structure of FeGeO3 is close to the ideal clinopyroxene in terms of the O atom arrangement and the tetrahedral chain configuration at ambient conditions. With pressure the lattice parameters and oxygen positions move closer to the ideal cubic closest packing (CCP) and the tetrahedral chain became more kinked with increasing pressure. However, a change in compression mechanism may occur around 4.5 GPa. All the polyhedra were homogeneously compressed above 4.5 GPa, whereas the MO6 exhibited compressibilities 3-4 times greater than that of the TO4 tetrahedra below 4.5 GPa. The Ge-O-Ge angle decreased with increasing pressure to 4.5 GPa and then remained constant. The close relationship between the kink angle and the relative polyhedral size suggests that this unusual compression behavior above 4.5 GPa may be caused by suppression of the extensive decrease of the Ge-O-Ge angle. The present results show that compression of pyroxenes with highly kinked tetrahedral chains is strongly effected by the kink angle.
• Compression mechanism and amorphization of portlandite, Ca(OH)(2): structural refinement under pressure

  T Nagai, T Ito, T Hattori, T Yamanaka

  PHYSICS AND CHEMISTRY OF MINERALS 27 (7) 462 - 466 0342-1791 2000/08 [Refereed][Not invited]
   

  In order to investigate compression mechanism and the pressure-induced amorphization of portlandite, Ca(OH)(2), the crystal structure has been refined up to 9.7 GPa using Rietveld analysis. Angular-dispersive synchrotron X-ray powder diffraction experiments were performed using a diamond anvil cell and an imaging plate at BL-18C in the Photon Factory at KEK, Japan. Compression behavior is highly anisotropic and the c axis is approximately 2.5 times as compressible as the a axis (beta(a) = 0.004, beta(c) = 0.011 GPa(-1)). Because the refined fractional coordinate, z, of the O atom increases linearly with pressure, compression along the c axis is due to the shortening of the interlayer spacing. The compression mechanism shows no change up to the amorphization pressure and is basically the same as that of brucite, Mg(OH)(2), observed below 10 GPa. The octahedral regularity of CaO6 approaches a regular configuration with pressure. The interlayer O...O distance is expected to be about 2.75 Angstrom at the amorphization pressure and should affect hydrogen bonding.
• Melting of portlandite up to 6 GPa

  H Fukui, O Ohtaka, T Nagai, T Katsura, K Funakoshi, W Utsumi

  PHYSICS AND CHEMISTRY OF MINERALS 27 (6) 367 - 370 0342-1791 2000/06 [Refereed][Not invited]
   

  Using the high-pressure differential thermal analysis (HP-DTA) system in a cubic multianvil high-pressure apparatus, we measured the melting points of portlandite, Ca(OH)(2), up to 6 GPa and 1000 degrees C. We detected endothermic behavior at the temperature and pressure conditions of 800 degrees C and 2.5 GPa, 769 degrees C and 3.5 GPa, 752 degrees C and 4.0 GPa, 686 degrees C and 5.0 GPa, and 596 degrees C and 6.0 GPa, respectively, due to melting of portlandite. By in situ X-ray studies under pressure, the melting of portlandite was observed at 730 degrees C and 4.32 GPa and at 640 degrees C and 5.81 GPa, respectively. Results of both HP-DTA and X-ray studies were consistent within experimental error. The melting is congruent and has a negative Clapeyron slope, indicating that liquid Ca(OH)(2) has higher densities than crystalline portlandite in this pressure range.
• Compression mechanism of brucite: An investigation by structural refinement under pressure

  T Nagai, T Hattori, T Yamanaka

  AMERICAN MINERALOGIST 85 (5-6) 760 - 764 0003-004X 2000/05 [Refereed][Not invited]
   

  Synchrotron X-ray powder diffraction study of brucite, Mg(OH)(2), was carried out in a diamond anvil cell with an imaging plate detector from 0.6 to 18.0 GPa at room temperature using the angular-dispersive technique on beamline BL-18C at the Photon Factory, KER, Japan. Using Rietveld analysis, unit-cell parameters as well as atomic positions of the O atoms in brucite have been successfully refined, taking into account the effects of preferred orientation. Variation of the c/a ratio with pressure indicates that the compression mechanism changes around 10 GPa, above which the compression behavior is isotropic. Based on the changes of the refined atomic positions of the O atoms with pressure, we conclude that the shortening of the interlayer distance controls compression below 10 GPa, whereas above this pressure compression of the oxygen sublattice is the dominant mechanism. Results of the structural refinements also suggest that the MgO6 octahedral regularity initially approaches a regular configuration with pressure, which then remains unchanged above 10 GPa.
• Crystal structure of the high pressure phase(II) in CuGeO3

  Akira Yoshiasa, Genta Yagyu, Tomokazu Ito, Takamitu Yamanaka, Takaya Nagai

  Zeitschrift fur Anorganische und Allgemeine Chemie 626 (1) 36 - 41 0044-2313 2000 [Refereed][Not invited]
   

  Crystal structures of the ambient pressure and temperature phase (phase I) and high pressure phase (phase II) in CuGeO3 were studied by means of the high pressure single-crystal X-ray diffraction method in a diamond anvil cell using high power X-ray generator and imaging plate detector. The pressure dependence of the atomic displacements in the phase I was investigated under the hydrostatic pressure of 0.1 MPa and 2.9 and 3.9 GPa. The lattice is particularly compressive in the b direction. In phase I the rippled layers are formed by the corner-shared chains of GeO4 tetrahedra and edge-linked planar CuO4. Major effects of pressure, directly related to the shortening of the b-axis, consist of an enhanced folding of the rippled layers towards the b-direction and of a shortening of the weak Cu-O bond. The crystal structure of phase II is monoclinic, a = 4.935(57), b = 6.754(14), c = 6.208(11) Å, β = 92.67(3)°, space group P21/c. The transition from phase I to II involves a corrugated arrangement of the both cation with some oxygens around the c-axis. Ge ion at the transition point of 6.4 GPa changes its coordination number from four-fold to five-fold, and Cu ion occupies a position of seven-fold site. The structure of phase II is explained as a slab structure having unique edge-and corner-sharing arrangements of GeO5 and CuO7 polyhedra. The average Ge-O and Cu-O distances in phase II is 1.92 and 2.17 Å, respectively, at 6.5 GPa.
• Pressure-dependent anharmonic coefficient of OH in portlandite by NIR-IR spectroscopy with DAC

  Keiji Shinoda, Takaya Nagai, Nobuyuki Aikawa

  Journal of Mineralogical and Petrological Sciences 95 (5) 65 - 70 1349-3825 2000 [Refereed][Not invited]
   

  NIR and IR absorption spectra of portlandite were measured to investigate the behavior of hydroxyls in portlandite under pressure with DAC. The IR absorption peak of fundamental OH stretching motion of portlandite at 3645cm-1 shifted to the lower wavenumber at the rate of -2.1 cm-1/GPa, and disappeared at 16.6 GPa. The secondary broad IR absorption peak at 3400cm-1 appeared over 8.3 GPa and its absorption was enhanced with applying pressure. The peak broadening of OH together with the absence of H2O molecules (5200cm-1) during compression suggests pressure-induced amorphization of portlandite. The NIR absorption peak due to overtone of OH stretching motion of portlandite at 7075cm-1 shifted to the lower wavenumber at the rate of -7.5 cm-1/GPa, which indicates more clearly increasing hydrogen bonding between layers in portlandite than the red shift of the IR peak. Assuming the Morse function as anharmonic potential energy of OH vibration, anharmonic coefficient of OH bond of portlandite against pressure was obtained from the pressure-dependent peak shift of the fundamental and overtone modes. The anharmonicity of OH bond in portlandite is enhanced with increasing pressure.
• Clinopyroxene-perovskite phase transition of FeGeO3 under high pressure and room temperature

  T Hattori, T Matsuda, T Tsuchiya, T Nagai, T Yamanaka

  PHYSICS AND CHEMISTRY OF MINERALS 26 (3) 212 - 216 0342-1791 1999/02 [Refereed][Not invited]
   

  In order to confirm the possible existence of FeGeO3 perovskite, we have performed in situ X-ray diffraction measurements of FeGeO3 clinopyroxene at pressures up to 40 GPa at room temperature. The transition of FeGeO3 clinopyroxene into orthorhombic perovskite is observed at about 33GPa. The cell parameters of FeGeO3 perovskite are a=4.93(2) Angstrom, b=5.06(6) Angstrom, c=6.66(3) Angstrom and V=166(3) Angstrom(3) at 40 GPa. On release of pressure, the perovskite phase transformed into lithium niobate structure. The previously reported decomposition process of clinopyroxene into Fe2GeO4 (spinel)+GeO2 (rutile) or FeO (wustite) +GeO2 (rutile) was not observed. This shows that the transition of pyroxene to perovskite is kinetically accessible compared to the decomposition processes un der low-temperature pressurization.
• Pressure and temperature dependence of EXAFS Debye-Waller factors in diamond-type and white-tin-type germanium

  A Yoshiasa, T Nagai, O Ohtaka, O Kamishima, O Shimomura

  JOURNAL OF SYNCHROTRON RADIATION 6 43 - 49 0909-0495 1999/01 [Refereed][Not invited]
   

  Extended X-ray absorption fine-structure (EXAFS) spectra near the Ge K-edge in diamond- and white-tin-type Ge under high temperature and high pressure were measured using a cubic-anvil-type apparatus (MAX90) with synchrotron radiation from the Photon Factory, Tsukuba, Japan. Pressure values up to 10.6 GPa were estimated on the basis of the isothermal equation of state of the diamond-type Ge within an accuracy of 0.4 GPa. Pressures for the same cell assembly were also determined by X-ray diffraction experiment using the NaCl scale. The diamond-type Ge is of great advantage to the pressure calibrant of EXAFS measurements at elevated temperature because a harmonic approximation can be applied up to 900 K. By the phase transition from diamond- to white-tin-type phases, with an increase in coordination number, Ge-Ge distances increase. A sixfold-coordinated Ge atom in the white-tin-type structure has crystallographically non-equivalent two kinds of nearest-neighbour distances [2.530(8) Angstrom and 2.697(8) Angstrom at 12.8 GPa]. The harmonic effective interatomic potential, V(u) = 1/2 alpha u(2), was evaluated from the contribution to the thermal vibration, where u is the deviation of the bond distance from the location of the potential minimum. The potential coefficient, alpha, at 0.1 MPa is essentially temperature independent and is 9.06 eV Angstrom(-2). At 9 GPa the potential coefficient is 9.71 eV Angstrom(-2). The effective interatomic potential is influenced not only by pressure but also by changes in coordination number. The high-pressure white-tin-type phase has a broader potential and a relatively larger mean square amplitude of vibration than the diamond-type phase.
• Effective pair potentials of NaCl- and CsCl-type KBr determined by X-ray absorption fine structure under pressure

  A Yoshiasa, T Nagai, K Murai, T Yamanaka, O Kamishima, O Shimomura

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 37 (2) 728 - 729 0021-4922 1998/02 [Refereed][Not invited]
   

  difference in effective pair potentials between the NaCl- and CsCl-type KBr has been investigated using the X-ray absorption fine structure (EXAFS) technique under pressure. In the potential parameter fitting, we have directly carried out the numerical integration of the EXAFS function and evaluated the precise effective pair potential. The effective pair potential is influenced not only by pressure but also by coordination numbers. The high pressure CsCl-type phase has broader effective pair potentials than the NaCl-type phase.
• In situ observation of ZrO2 phases at high pressure and temperature

  O Ohtaka, T Nagai, T Yamanaka, T Yagi, O Shimomura

  PROPERTIES OF EARTH AND PLANETARY MATERIALS AT HIGH PRESSURE AND TEMPERATURE 101 429 - 433 0065-8448 1998 [Refereed][Not invited]
   

  Two kinds of in situ observation have been performed in order to reveal the high-pressure and -temperature polymorphism of ZrO2 and to clarify the crystal structures for these polymorphs. By using a diamond anvil cell and a laser heating system, ZrO2 was heated at about 1000 degrees C under high pressures up to 30 GPa. Thermally quenched samples were investigated by X ray diffraction under high pressure. As a result, a hexagonal phase was formed above 20 GPa while a mixture of orthoI and orthoII was observed below 20 GPa. By using a cubic anvil type device and synchrotron radiation, diffraction data in the temperature range up to 900 degrees C at 8 to 13 GPa were collected. The results indicated that ZrO2 crystallizes in a distorted fluorite structure under these P-T conditions.
• Pressure-induced structural modifications of metagermanates at room temperature: In situ XRD and EXAFS studies

  T Nagai, O Ohtaka, A Yoshiasa, T Yamanaka, O Shimomura

  PROPERTIES OF EARTH AND PLANETARY MATERIALS AT HIGH PRESSURE AND TEMPERATURE 101 385 - 391 0065-8448 1998 [Refereed][Not invited]
   

  In situ X ray diffraction (XRD) and extended X ray absorption fine structure (EXAFS) measurements under high pressure and at room temperature were performed in order to verify the possibility of a pressure-induced amorphization of MgGeO3-high-clinoenstatite and CaGeO3-wollastonite. We found that the two metagermanates were transformed into new metastable phases without the amorphization. For MgGeO3-high-clinoenstatite, a new reflection, which could not be assigned as its known high-pressure polymorphs, could be observed above 23 GPa. For CaGeO3-wollastonite, EXAFS measurements under high pressure were conducted using MAX90. The observed pressure dependence of the Ge-O distance can suggest the existence of a metastable intermediate phase between wollastonite and perovskite. The intermediate phase corresponds to a rhodonite-like structure, which was proposed by a previous XRD experiments. These transitions, which were observed in the two metagermanates, suggest to be kinetically favored processes under room temperature compression. Such metastable pathways during phase transitions can be described as typical examples of the Ostwald step rule.
• Phase relations and physical properties of Fe2SiO4-Fe3O4 solid solution under pressures up to 12GPa

  T Yamanaka, H Tobe, T Shimazu, A Nakatsuka, Y Dobuchi, O Ohtaka, T Nagai, E Ito

  PROPERTIES OF EARTH AND PLANETARY MATERIALS AT HIGH PRESSURE AND TEMPERATURE 101 451 - 459 0065-8448 1998 [Refereed][Not invited]
   

  Phase study of the Fe2SiO4-Fe3O4 solid solution system has been carried out under high pressures up to 12 GPa at 1200 degrees C by multianvil apparatus. A complete spinel solid solution between Fe3O4 and gamma-Fe2SiO4 has been found at pressures over 10 GPa. gamma-Fe2SiO4 with a normal spinel structure is stable at pressures above 7 GPa. A spinelloid structure similar to aluminosilicate V (Pmma) in the NiAl2O4-Ni2SiO4 system is found in a wide intermediate compositional range x=0.37 to 0.73 in Fe3-xSixO4 at pressures between 3 and 9 GPa. X ray single-crystal structure analyses of several samples of Fe3-xSixO4 spinel indicate the site occupancy of (Fe1-x+y3+Six-y4+) [Fe1+x2+Fe1-x-y3+Siy4+] O-4. This cation distribution affects the electrical conductivity mainly because of the electron hopping between Fe3+ and Fe2+ in the octahedral site. Measurement of the electrical conductivity of the spinel solid solution has been made at low temperatures in the range 80 to 300 K. The transition temperature of the Verwey order between Fe3+ and Fe2+ decreases with the Si content in Fe3-xSixO4 and the energy gap becomes smaller with Si.
• Pressure Induced Structural Phase Transition of CdI2-type PbI2

  Y. Matsumoto, O. Ohtaka, M. Kikuchi, T. Nagai, T. Yamanaka, O. Shimomura

  Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 7 341 - 343 1348-1940 1998 [Refereed][Not invited]
   

  X-ray in-situ observation of PbI2 under high pressure and temperature up to 13 GPa and 600 °C was conducted by means of MAX 90 system and synchrotron radiation. Two high pressure phases were newly found to appear at 10 GPa, 200 °C (phase VII) and at 13 GPa, 600 °C (phase VIII) respectively. The phase relation under pressure was drawn by combining the present data and those reported. In the course of releasing pressure, phase VIII was retained down nearly to 1 GPa and reverted directly to the ambient pressure phase on the complete release of pressure, while phase VII transformed to a metastable phase at 3 GPa. Obtained diffraction patterns of phase VII and VIII were indexed on the basis of monoclinic symmetry. Baddeleyite type structure is proposed for phase VII. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.
• Nucleation and Growth Kinetics of the a-Quartz-Coesite Transformation Using both Powder and Single Crystal Samples

  T. Nagai, S. Mori, O. Ohtaka, T. Yamanaka

  Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 7 125 - 127 1348-1940 1998 [Refereed][Not invited]
   

  The kinetics of the α-quartz-coesite transformation was investigated at 4 GPa using both powder and single crystal samples. The results could be analyzed by the Avrami rate equation. Determined exponent n gave values close to 1 for both powder and single crystal experiments. This fact suggests that the growth process is able to control the kinetics. Observations by an optical microscopy in partly transformed single crystals indicate that the coesite phase homogeneously nucleates on the surface of the crystal and grows into the interior. In the case of powder samples, the empirically activation energy of the transformation was determined as 200 (±30) kJ/mol. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.
• Phase Transformations and Lattice Instability of Earth Interiors under High Pressure and Stress Field

  T. Yamanaka, T. Nagai

  Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 7 34 - 39 1348-1940 1998 [Refereed][Not invited]
   

  Phase transformations in earth interiors is discussed on the basis of the lattice instability under the condition of homogeneous or inhomogeneous stress field. X-ray diffractometry and molecular dynamics calculation elucidate, the atomic positional displacement and fluctuation of crystallographic translation operation resulting in the lattice deformations. The lattice instability is clarified by diffraction profile analysis. Reversible pressure-induced transformations come out from the elastic deformation. On the other hand irreversible transformation are caused by the plastic deformation. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.
• First observation of FeGeO3-perovskite under high pressure

  T Nagai, T Hattori, T Tsuchiya, T Yamanaka

  SOLID STATE COMMUNICATIONS 107 (5) 223 - 225 0038-1098 1998 [Refereed][Not invited]
   

  Pressure-induced phase transition from high pressure clinopyroxene type FeGeO3 to its perovskite polymorph has been observed for the first time. X-ray measurements were conducted at 40 GPa and at room temperature. The material is indexed on an orthorhombic lattice, with unit cell parameters a = 4.93 +/- 0.02 Angstrom, b = 5.06 +/- 0.05 Angstrom, c = 6.66 +/- 0.03 Angstrom and V = 166.1 +/- 0.8 Angstrom(3) at 40 GPa. The pressure-induced transition to FeGeO3-perovskite occurs during room temperature compression of the high pressure clinopyroxene type of FeGeO3. Furthermore, FeGeO3-perovskite was transformed into the lithium niobate structure during decompression This phase was indexed on a hexagonal lattice, with unit cell parameters a = 5.05 +/- 0.04 Angstrom, c = 14.2 +/- 0.2 Angstrom and V = 313.6 +/- 1.2 Angstrom(3) at ambient pressure. (C) 1998 Elsevier Science Ltd. All rights reserved.
• Stability of C70Fx crystalline under high pressure

  S Kawasaki, T Aketa, F Okino, H Touhara, T Hattori, T Nagai, T Yamanaka

  SOLID STATE COMMUNICATIONS 108 (10) 749 - 752 0038-1098 1998 [Refereed][Not invited]
   

  In order to study the stability range of C70Fx under high pressure at room temperature, in situ X-ray diffraction experiments were performed under pressures up to 6.7 GPa. It was found that C70Fx transforms from a crystalline to an amorphous phase at about 5.5 GPa. The pressure-volume relation of C70Fx was also investigated. The bulk modulus and its pressure derivative were determined to be 26.6 (1.8) GPa and 3.0 (0.7), respectively. (C) 1998 Elsevier Science Ltd. All rights reserved.
• Structural modifications of CaGeO3-wollastonite under room temperature pressurization

  T Nagai, T Yamanaka

  PHYSICS AND CHEMISTRY OF MINERALS 25 (1) 1 - 7 0342-1791 1997/11 [Refereed][Not invited]
   

  In-situ X-ray diffraction measurements of CaGeO3-wollastonite at high pressure at room temperature have been performed using a diamond anvil cell with an X-ray source. A new structural modification of CaGeO3-wollastonite is observed at about 6GPa and the characteristic reflections of the high pressure form are preserved on decompression to an ambient pressure. A rhodonite-like structure is proposed as a high pressure form from the crystal chemical consideration. The rhodonite-like phase is further transformed into a perovskite-form at about 15 GPa. The rhodonite-like-form of CaGeO3 seems not to be a stable phase from the heating experiments under high pressures. The metastable transition path from the wollastonite to the perovskite polymorph through the rhodonite-like structure is kinetically favored under room temperature pressurization. No pressure-induced amorphization is observed during the transition into the perovskite-form, although the transition is accompanied by the coordination change of Ge atoms from fourfold to sixfold.
• Kinetics studies of the α-quartz-coesite transformation of SiO_2

  NAGAI Takaya, OHTAKA Osamu, YAMANAKA Takamitsu

  Mineralogical journal 19 (4) 147 - 154 0544-2540 1997/10 [Refereed][Not invited]
  
• 格子安定性の圧力効果:―弾性・塑性格子変形―

  山中 高光, 永井 隆哉, 服部 高典, 土屋 卓久

  日本結晶学会誌 The Crystallographic Society of Japan 39 68 - 68 0369-4585 1997 [Refereed]
  
• Mechanism of pressure-induced amorphization

  T Yamanaka, T Nagai, T Tsuchiya

  ZEITSCHRIFT FUR KRISTALLOGRAPHIE 212 (6) 401 - 410 0044-2968 1997 [Refereed][Not invited]
   

  Several crystalline substances have been found to be transformed into the amorphous state under compressed condition at kinetically low temperature. Dynamical lattice-instability due to elastic deformation by shear and stress induces the reversible amorphization, some of which produces memory glass. On the other hand the irreversible modes are attributed to the plastic deformation by the nucleation of high-pressure form in the parent lattice but thermal energy is not kinetically high enough to provide the large crystallite size coherent to the X-ray radiation. They can be defined as X-ray amorphous. These reversible and irreversible transformations arise from the hindrance to sufficient atomic mobility. These pressure-induced amorphizations are the precursor phenomena of the phase transformation to high-pressure polymorphs. Successive structure changes of the pressure-induced amorphization are investigated under various pressure and temperature by X-ray diffractometry, EXAFS and Raman spectroscopy. The amorphization has been also simulated by the molecular dynamics.
• Pressure-induced Amorphization of Silicates and Germanates

  Takaya Nagai

  The Review of High Pressure Science and Technology 4 (1) 35 - 41 1348-1940 1995 [Refereed][Not invited]
   

  Pressure-induced amorphization is a kinetically hindered phenomenon. The amorphization has been a topic not only in the field of high pressure physics but also in the field of earth science for the last decade. The amorphization of minerals will play an important role to understand the mechanism of deep-forcus earthquakes in the subduction zone, the rheological properties of the slub and the recycling water in the mantle, and so on. In this article, the pressure-induced amorphization of silicates and germanates will be reviewed from the view point of the crystal structures and our resent experiments using the synchrotron radiation will be introduced. © 1995, The Japan Society of High Pressure Science and Technology. All rights reserved.
• Pressure-induced amorphization of Mg2GEO4-olivine.

  NAGAI T, YANO K, DEJIMA M, YAMANAKA T

  Mineral J Japan Association of Mineralogical Sciences 17 (4) 151 - 157 0544-2540 1994/10 [Refereed][Not invited]
   

  In-situ X-ray diffraction measurements were conducted for Mg₂GeO₄-olivine under high pressure at room temperature by using a diamond anvil cell(DAC) and a synchrotron radiation source in the National Institute for High Energy Physics as well as a conventional laboratory X-ray source, in order to clarify the possibility of a pressure-induced amorphization. The isothermal bulk modulus K₀=70(±5)GPa is obtained. The Mg₂GeO₄-olivine transforms to 'X-ray amorphous state' below 30GPa and the amorphous state is preserved during the decompression process to 0.1 MPa. The local structural instability caused by the change of the coordination of Ge atoms is likely to lead to the pressure-induced amorphization.
• 地球内部700km以深で地震が起こらないのはなぜか?

  永井隆哉

  化学と工業 46 (4) 677 - 678 0022-7684 1993/04 [Refereed][Not invited]
  

Books etc

• 鉱物・宝石の科学事典

  日本鉱物科学会 
  朝倉書店 2019 (ISBN: 9784254162769)
• マイクロビームアナリシス・ハンドブック

  (Joint work第7章2節 X 線・放射光利用分析法)
  オーム社 2014/06
• 地球惑星科学入門

  (Joint work)
  北海道大学出版会 2010 (ISBN: 9784832982192)
• 地球の変動と生物進化

  (Joint work)
  北海道大学出版会 2008

Conference Activities & Talks

• NMR study on Al local structures in Al-bearing CaTiO3 perovskite  [Not invited]

  Takaya NAGAI, Xianyu XUE

  日本鉱物科学会2023年年会  2023/09
• Structural change of Al-bearing CaTiO3 perovskite 2  [Not invited]

  Takaya NAGAI, Naoki TAKAKURA, Yosuke MATSUMOTO, Yu TAGUCHI, Xianyu XUE

  日本鉱物科学会2022年年会  2022/09
• Structural change of Al-bearing CaTiO3 perovskite  [Not invited]

  Takaya NAGAI, Naoki TAKAKURA, Yosuke MATSUMOTO, Xianyu XUE

  日本鉱物科科学会  2021/09
• Investigation on the crystal growth/dissolution mechanisms by using the 2-D visualization technique with fluorescent probes

  川野潤, 矢崎誠, 豊福高志, 豊福高志, 長井裕季子, 長井裕季子, TENG Henry, 永井隆哉

  日本鉱物科学会年会講演要旨(Web)  2019
• Investigation on the crystal growth/dissolution mechanisms by 2-D visualization of pH and ionic concentration

  川野潤, 矢崎誠, 豊福高志, 豊福高志, 長井裕季子, 長井裕季子, TENG Henry, 永井隆哉

  結晶成長国内会議予稿集(CD-ROM)  2019
• In-situ observation of pressure induced hydrogen bond symmetrization in a hydrous mineral

  佐野亜沙美, 服部高典, 小松一生, 鍵浩之, 永井隆哉

  量子ビームサイエンスフェスタ(Web)  2019
• Incorporation of Ga³⁺ into CaTiO₃ perovskite

  永井隆哉, 大黒正貴, 高倉直樹, 井上徹, 新名亨

  日本鉱物科学会年会講演要旨(Web)  2019
• 高圧下におけるCaTiO₃-CaM³⁺O_2.5系ペロブスカイトの固溶について

  永井隆哉, 大黒正貴, 高倉直樹, 井上徹, 井上徹, 新名亨

  高圧討論会講演要旨集  2019
• 水溶液中における非晶質炭酸マグネシウムの形成と結晶化プロセス

  田中淳也, 川野潤, 永井隆哉, TENG Henry

  日本地球惑星科学連合大会予稿集(Web)  2018
• 溶解するCaCO₃表面近傍におけるpH/Ca濃度変化の2次元可視化

  川野潤, 豊福高志, 豊福高志, 長井裕季子, 長井裕季子, 藤昇一, 田中淳也, 永井隆哉

  日本鉱物科学会年会講演要旨(Web)  2018
• 人工飼育造礁サンゴの微細組織観察

  甕聡子, 富岡尚敬, 兒玉優, 川野潤, 波利井佐紀, 永井隆哉, 渡邊剛, 伊藤元雄

  日本鉱物科学会年会講演要旨(Web)  2018
• Formation and transformation of amorphous magnesium carbonate in aqueous solution with various Mg/CO₃ ratios

  田中淳也, 川野潤, 永井隆哉, TENG Henry

  日本鉱物科学会年会講演要旨(Web)  2018
• 含水鉱物における圧力誘起水素結合対称化

  佐野亜沙美, 服部高典, 小松一生, 鍵裕之, 永井隆哉

  日本中性子科学会年会講演概要集  2018
• 高圧下におけるCaTiO₃ペロブスカイトへのCaAlO_2.5成分の固溶量

  永井隆哉, 松本洋輔, 井上徹, 井上徹, 新名亨

  高圧討論会講演要旨集  2018
• Visualization of dissolution process of carbonate crystals in aqueous solutions by using fluorescent probes

  川野潤, 豊福高志, 豊福高志, 長井裕季子, 長井裕季子, 田中淳也, 永井隆哉

  結晶成長国内会議予稿集(CD-ROM)  2018
• 酸素欠陥ペロブスカイトの高圧下での安定性

  永井隆哉, 今野新之介, 井上徹, 井上徹, 新名亨

  高圧討論会講演要旨集  2017
• 鉱物の溶解にともなうpH変化の2次元イメージング  [Not invited]

  川野潤, 西村楓, 豊福高志, 長井裕季子, 河田佐知子, TENG Henry, 永井隆哉

  日本鉱物科学会年会講演要旨(Web)  2017  Japan Association of Mineralogical Sciences
   

  Here we succeeded to visualize the two-dimensional distribution of pH around dissolving calcium carbonate crystals and its change with time, by using the fluorescent probe 8-hydroxypyrene-1,3,6-trisul-fonic acid (HPTS). The results showed that pH increases and saturated rapidly just above a surface, while pH increases gradually at an area some distance away from the surface. This technique should provide the useful information to understand the dissolution kinetics of minerals and can be applied to various systems.
• Direct observation of pH/ionic concentration change around dissolving crystal in aqueous solution  [Not invited]

  川野潤, 豊福高志, 長井裕季子, 田中淳也, 上田暁之, 西村楓, 永井隆哉

  結晶成長国内会議予稿集(CD-ROM)  2017
• Stability of oxygen‐deficient perovskite at high pressure and temperature  [Not invited]

  永井隆哉, 今野新之介, 井上徹, 井上徹, 新名亨

  日本鉱物科学会年会講演要旨(Web)  2017
• Thermal decomposition of kaolinite and chlorite as a proxy for earthquake slip along an imbricate thrust fault in an accretionary prism  [Not invited]

  Masumoto Hirokazu, Kameda Jun, Nagai Takaya, Arima Hiroshi, Sugiyama Kazumasa, Yamamoto Yuzuru

  Annual Meeting of the Geological Society of Japan  2017  The Geological Society of Japan
   

  [Program canceled for typhoon] Program canceled for typhoon. However, This abstract is quotable and viewable on PDF.
• 造礁サンゴ骨格形成に共生藻と海水Mg/Caモル比が与える影響

  甕聡子, 川野潤, 波利井佐紀, 兒玉優, 富岡尚敬, 伊藤元雄, 渡邊剛, 永井隆哉

  日本鉱物科学会年会講演要旨(Web)  2017
• CaSiO₃ペロブスカイトへのNa⁺とLa³⁺のカップル固溶限界について  [Not invited]

  永井隆哉, 高川智成, 井上徹, 新名亨

  高圧討論会講演要旨集  2016/10
• CaTiO₃‐CaM³⁺O_2.5系ペロブスカイトへの水の固溶に関する研究  [Not invited]

  今野新之介, 永井隆哉, 井上徹, 新名亨

  高圧討論会講演要旨集  2016/10
• ダイアスポアの脱水反応のカイネティクス  [Not invited]

  永井隆哉, 杉浦晃希, 川野潤, 小田めぐみ

  日本鉱物科学会年会講演要旨集  2016/09
• 成長/溶解するCaCO₃近傍におけるpH/Ca濃度変化の可視化の試み  [Not invited]

  川野潤, 豊福高志, 長井裕季子, 河田佐知子, 永井隆哉

  日本鉱物科学会年会講演要旨集  2016/09  Japan Association of Mineralogical Sciences
   

  We have recently started an attempt to visualize the distribution of pH and Ca concentration around CaCO₃ crystals which inorganically grows or dissolves, by applying the method used for the research on the biogenic calcification of foraminifers.The pH change near a dissolved calcite and aragonite surface has been succeeded, which may provide new insights into both inorganic and biogenic formation mechanism of CaCO_3.
• Structural variations accompanied by thermal expansion of diaspore  [Not invited]

  Sugiura Teruki, Nagai Takaya, Arima Hiroshi, Sugiyama Kazumasa

  Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences  2016  Japan Association of Mineralogical Sciences
   

  Single crystal X-ray diffraction experiments for diaspore have been worked in the temperature range from 22 to 425 ºC, in order to understand detailed mechanism of thermal expansion. Temperature variations of the cell parameters indicate that thermal expansion of the a-axis is higher than that of the b-axis or the c-axis. The results of the structure refinement suggest such anisotropic behavioris due to thermal expansion of the empty cavities in the structure of diaspore.
• FIB‐TEMによる六角平板状vateriteの内部組織観察  [Not invited]

  川野潤, 川野潤, 鶴本千尋, 三宅亮, 永井隆哉

  結晶成長国内会議予稿集(CD-ROM)  2015/10
• CaSiO₃ペロブスカイトへのNa⁺とLa³⁺の固溶の検討  [Not invited]

  永井隆哉, 高川智成, 井上徹, 新名亨

  日本鉱物科学会年会講演要旨集  2015/09
• J‐PARC,PLANETでの高温高圧中性子回折 その場観察によるCa(OD)₂の水素位置決定  [Not invited]

  飯塚理子, 小松一生, 佐野亜沙美, 服部高典, 後藤弘匡, 永井隆哉, 鍵裕之, 八木健彦

  物構研サイエンスフェスタ要旨集  2015
• CaCO₃クラスターの安定構造と不純物効果の理論的検討  [Not invited]

  KAWANO JUN, MAEDA SATOSHI, NAGAI TAKAYA

  結晶成長国内会議予稿集(CD-ROM)  2014/11
• CaCO₃クラスターにおける不純物効果の理論的解析  [Not invited]

  KAWANO JUN, MAEDA SATOSHI, NAGAI TAKAYA

  日本鉱物科学会年会講演要旨集  2014/09
• ブルーサイトのH‐D相互拡散の速度論的研究  [Not invited]

  MASUDA MANAMI, NAGAI TAKAYA, KAWANO JUN

  日本鉱物科学会年会講演要旨集  2014/09
• PLANETビームラインでの中性子回折実験から見えてきた高温高圧下でのCa(OD)₂の結晶構造変化  [Not invited]

  NAGAI TAKAYA, SANO ASAMI, HATTORI TAKANORI

  日本鉱物科学会年会講演要旨集  2014/09
• Ca(OD)₂の高圧下での熱膨張  [Not invited]

  NAGAI TAKAYA, SANO ASAMI, IIZUKA RIKO, KAGI HIROYUKI, HATTORI TAKANORI

  物構研サイエンスフェスタ要旨集  2014
• Ca(OD)₂の高圧下での熱膨張―PLANETでの高温高圧中性子回折実験―  [Not invited]

  NAGAI TAKAYA, SANO ASAMI, IIZUKA RIKO, KAGI HIROYUKI, HATTORI TAKANORI

  物構研サイエンスフェスタ要旨集  2014
• PLANETでの高温高圧中性子回折実験―Ca(OD)₂の高温高圧下の結晶構造変化―  [Not invited]

  NAGAI TAKAYA, SANO ASAMI, IIZUKA RIKO, KAGI HIROYUKI, HATTORI TAKANORI

  高圧討論会講演要旨集  2013/10
• 枝状サンゴ骨格の微細組織観察  [Not invited]

  MOTAI SATOKO, NAGAI TAKAYA, SOWA KOKI, KAWANO JUN, WATANABE TSUYOSHI

  日本鉱物科学会年会講演要旨集  2013/09
• Aragonite表面における2価陽イオンの安定性:第一原理計算による考察  [Not invited]

  KAWANO JUN, SAKUMA HIROSHI, NAGAI TAKAYA

  日本鉱物科学会年会講演要旨集  2013/09
• Kinetic study of H-D exchange in brucite

  NAGAI Takaya, HINO Yusuke, KAWANO Jun

  日本鉱物科学会年会講演要旨集  2013/09
• ブルーサイトのH‐D交換反応の速度論的研究  [Not invited]

  NAGAI TAKAYA, HINO YUSUKE, KAWANO JUN

  日本鉱物科学会年会講演要旨集  2013/09
• 含水鉱物の脱水反応へのHとDの置換効果  [Not invited]

  NAGAI TAKAYA, KOBAYASHI SAWA, HINO YUSUKE

  高圧討論会講演要旨集  2010/10
• Infrared absorption spectra of delta-AlOOH and its deuteride at high pressure and implication to pressure response of the hydrogen bonds  [Not invited]

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

  INTERNATIONAL CONFERENCE ON HIGH PRESSURE SCIENCE AND TECHNOLOGY, JOINT AIRAPT-22 AND HPCJ-50  2010  IOP PUBLISHING LTD
   

  Infrared absorption spectra of delta-AlOOH and its deuterated form (delta-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(-1) and 1330 cm(-1) involving vibrations of hydrogen and oxygen atoms shifted to higher frequencies with increasing pressure up to 10 and 12 GPa for delta-AlOOH and delta-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.
• 熱重量測定による脱水反応速度への同位体効果  [Not invited]

  NAGAI TAKAYA, KOBAYASHI SAWA

  日本鉱物科学会年会講演要旨集  2010
• X線発光分光法による200GPaまでのMg‐ペロブスカイト中の3価鉄のスピン状態  [Not invited]

  藤野清志, 西尾浜根大輔, 瀬戸雄介, 佐多永吉, 永井隆哉, 石堂知基, 鈴木啓介, LIN Li, 新名亨, 入舩徹男, 石井啓文, 平岡望, CAI Yong‐Qiang, TSUEI Kur‐Ding

  日本鉱物科学会年会講演要旨集  2009  Japan Association of Mineralogical Sciences
   

  To estimate the spin state of iron in Mg-perovskite in the lower mantle, the spin state of ferric iron in synthesized Mg-perovskite was measured at pressures up to 200 GPa at room temperature by X-ray emission spectroscopy at SPring-8. The result indicates that the spin number of ferric iron in Mg-perovskite began to decrease at pressure around 120 GPa with increasing pressure, but remained intermediate between high spin and low spin at 200 GPa. This result indicates that the spin state of ferric iron in Mg-perovskite does not become low spin in the lower mantle if the temperature gradient of the spin transition is positive.
• 高圧下における二酸化炭素(CO₂‐V)の結晶構造  [Not invited]

  SETO YUSUKE, HAMANE DAISUKE, OKADA TAKU, YAGI TAKEHIKO, NAGAI TAKAYA

  日本鉱物科学会年会講演要旨集  2009
• CaTiO₃ペロブスカイトへの3価陽イオンの固溶について  [Not invited]

  KANEMURA HIROSHI, NAGAI TAKAYA, MOTAI SATOKO

  日本鉱物科学会年会講演要旨集  2009
• Na⁺La³⁺Ti₂O₆‐CaTiO₃系ペロブスカイトの固溶関係  [Not invited]

  ISHIGURO NATSUKI, NAGAI TAKAYA

  日本鉱物科学会年会講演要旨集  2009
• 中性子回折実験によるCa(OD)₂の重水素位置の精密化  [Not invited]

  NAGAI TAKAYA, SANO ASAMI, KAGI HIROYUKI, IIZUKA RIKO, KURIBAYASHI TAKAHIRO

  日本鉱物科学会年会講演要旨集  2009
• 固体CO₂‐V相の結晶構造について  [Not invited]

  SETO YUSUKE, HAMANE DAISUKE, NAGAI TAKAYA, FUJINO KIYOSHI

  高圧討論会講演要旨集  2008/11
• 下部マントルにおける鉄のスピン転移  [Not invited]

  FUJINO KIYOSHI, HAMANE DAISUKE, SETO YUSUKE, SATA NAGAYOSHI, NAGAI TAKAYA, ISHIDO TOMOKI, SUZUKI KEISUKE, SHINMEI TOORU, IRIFUNE TETSUO, ISHII HIROFUMI, HIRAOKA NOZOMU, CAI Y. Q

  高圧討論会講演要旨集  2008/11
• δ‐AlOOHの圧縮挙動への温度効果  [Not invited]

  NAGAI TAKAYA, SANO ASAMI, KAGI HIROYUKI, YAGI TAKEHIKO, USHIJIMA DAICHI, IIZUKA RIKO

  高圧討論会講演要旨集  2008/11
• 鉄・アルミを固溶したペロブスカイト相の圧縮挙動と鉄のスピン状態  [Not invited]

  HAMANE DAISUKE, FUJINO KIYOSHI, SETO YUSUKE, SATA NAGAYOSHI, NAGAI TAKAYA, SHINMEI TOORU, IRIFUNE TETSUO, ISHII HIROFUMI, HIRAOKA NOZOMU, CAI Y. Q

  日本鉱物科学会年会講演要旨集  2008
• Mg‐ペロブスカイトにおける3価鉄のスピン転移  [Not invited]

  FUJINO KIYOSHI, HAMANE DAISUKE, SETO YUSUKE, SATA NAGAYOSHI, NAGAI TAKAYA, SUZUKI KEISUKE, ISHIDO TOMOKI, SHINMEI TOORU, IRIFUNE TETSUO, ISHII HIROFUMI, HIRAOKA NOZOMU, CAI Y. Q

  日本鉱物科学会年会講演要旨集  2008
• CaTiO₃‐NdAlO₃ペロブスカイトの透過電子顕微鏡による転移双晶の観察  [Not invited]

  KANEMURA HIROSHI, SETO YUSUKE, HAMANE DAISUKE, NAGAI TAKAYA

  日本鉱物科学会年会講演要旨集  2008
• Microstructure Observations on Coral Skelton  [Not invited]

  Motai Satoko, Nagai Takaya, Sakamoto Naoya, Sowa Kohki, Watanabe Tuyoshi, Yurimoto Hisayoshi

  Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences  2008  Japan Association of Mineralogical Sciences
   

  Mineral phase identification of the coral skeletal microstructure is important for reconstructing the paleo-climate. Especially, chemical composition of Porites sp. is widely used as a paleo-environment variant. For example, it is believed that Sr/Ca ratio in coral skeletons is sensitive to temperature of seawater. Recently, Greegor et al. (1997) reported that as much as 40% of strontium (Sr) in coral aragonite existed as a SrCO₃ end member by using XANES and EXAFS. This should be a very serious problem, when we apply the Sr/Ca ratio to reconstruct the paleo-environment. However, since there has been no direct mineral identification of SrCO₃, we have carefully observed Porites sp. by FE-ASEM and ATEM in order to identify mineral phases in the coral skeletal.
• J-PARCの共用開始と中性子利用高圧研究の戦略

  内海渉, 阿部淳, 服部高典, 深澤裕, 山内宏樹, 井川直樹, 鍵裕之, 有馬寛, 荒川雅, 小松一生, 八木健彦, 永井隆哉, HARJO Stefanus, 相澤一也, 大友季哉, 神山崇

  高圧討論会講演要旨集  2008
• Oxidation of Fe₃C at high pressure and high temperature

  Nagai Takaya, Seto Yusuke, Hamane Daisuke, Sata Nagayoshi, Fujino Kiyoshi

  Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences  2008  Japan Association of Mineralogical Sciences
   

  We have investigated the stability of Fe₃C-cementite at high pressure and high temperature, because there has been a little knowledge about that. In the 2007 annual meeting, we reported a preliminary result that Fe₃C may be transformed into Fe₇C₃ + Fe at high pressure and high temperature. However, it was strange that we observed not Fe but FeO in the run products. We used NaCl as thermal insulating material in a diamond anvil cell (DAC). Since it is known that NaCl often adsorb H2O, it may cause the oxidation of Fe. Therefore, we used different thermal insulating materials (Al₂O₃ and CaSiO₃) in order to see some effects of those thermal insulators.
• 高温高圧下におけるFeAlO₃の相関係

  和田光平, 西山宣正, 入舩徹男, 永井隆哉, 浜根大輔, 藤野清志

  高圧討論会講演要旨集  2008
• FeAlO₃‐MgSiO₃系の高圧相関系とペロブスカイト相の体積弾性率  [Not invited]

  HAMANE DAISUKE, SETO YUSUKE, NAGAI TAKAYA, FUJINO KIYOSHI

  高圧討論会講演要旨集  2007/11
• 高圧下における炭酸塩分解反応  [Not invited]

  SETO YUSUKE, HAMANE DAISUKE, NAGAI TAKAYA, FUJINO KIYOSHI

  高圧討論会講演要旨集  2007/11
• X線発光分光法による下部マントル条件下でのMg―ペロブスカイト中の3価鉄のスピン転移  [Not invited]

  FUJINO KIYOSHI, SETO YUSUKE, HAMANE DAISUKE, SATA NAGAYOSHI, SHINMEI TOORU, IRIFUNE TETSUO, SUZUKI KEISUKE, NAGAI TAKAYA, ISHII HIROFUMI, CAI Y. Q

  高圧討論会講演要旨集  2007/11
• 高圧下中性子回折実験による鉱物中の水素位置決定  [Not invited]

  NAGAI TAKAYA, KAGI HIROYUKI, PARISE JOHN B

  高圧討論会講演要旨集  2007/11
• ポストペロブスカイト相転移へのFeAlO_3成分の影響

  HAMANE D., FUJINO K., SETO Y., NAGAI T.

  日本鉱物学会・学術講演会,日本岩石鉱物鉱床学会学術講演会講演要旨集  2007/09  Japan Association of Mineralogical Sciences
   

  The incorporations of ferric iron and aluminum into perovskite influence the transition pressure to the post-perovskite phase. Here, we report the effect of the incorporation of FeAlO3 into MgSiO3 perovskite on the post-perovskite transition based on the laser heated diamond anvil cell and high-pressure and temperature in-situ X-ray diffraction experiments. Results demonstrate that a single perovskite is stable up to 143 GPa and 2500 K, and perovskite and post-perovskite coexist at 157-162 GPa and 1600-2500 K for the pressure scales by Tsuchiya (2003). Post-perovskite formed as single phase at 176-178 GPa and 1600-2600 K. The post-perovskite transition pressure in Mg0.85Fe0.15Al0.15Si0.85O3 was much higher than that in MgSiO3.
• Fe_3Cの高温高圧下での安定性について

  NAGAI Takaya, SETO Yusuke, HAMANE Daisuke, SATA Nagayoshi, FUJINO Kiyoshi

  日本鉱物学会・学術講演会,日本岩石鉱物鉱床学会学術講演会講演要旨集  2007/09  Japan Association of Mineralogical Sciences
   

  We performed high pressure and high temperature experiments at the pressure range between 30 and 100 GPa, at 1500 – 2000 K. Although it was not easy to identify diffraction peaks observed at high pressure and high temperature, diffraction patterns observed for recovered samples show the existence of crystalline Fe₇C₃. It is also noted that FeO is observed with Fe₇C₃ in most of the experiments. We used NaCl or Al₂O₃ disks as thermal insulator with the sample. FeO could be observed in the both experiments. We could not detect melt in the diffraction patterns obtained at high pressure and high temperature. Results in this study suggest that Fe₃C is not stable at high pressure and high temperature and transforms into Fe₇C₃ + Fe, although it is still discussing why Fe is oxidized to FeO in DACs.
• Phase relation in the Ca^<2+>Ti^<4+>O_3-Y^<3+>Ga^<3+>O_3 system

  MOTAI Satoko, NAGAI Takaya, SETO Yusuke

  日本鉱物学会・学術講演会,日本岩石鉱物鉱床学会学術講演会講演要旨集  2007/09
• Mineral phase identification of coral skeletal microstructure  [Not invited]

  K. Sowa, T. Watanabe, Y. Seto, S. Motai, T. Nagai

  GEOCHIMICA ET COSMOCHIMICA ACTA  2007/08  PERGAMON-ELSEVIER SCIENCE LTD
  
• MnSiO₃の高圧相関係とペロブスカイト構造  [Not invited]

  SUZUKI KEISUKE, FUJINO KIYOSHI, HAMANE DAISUKE, SETO YUSUKE, NAGAI TAKAYA

  日本鉱物科学会年会講演要旨集  2007
• MgSiO₃‐perovskiteへの鉄とアルミの固溶  [Not invited]

  HAMANE DAISUKE, FUJINO KIYOSHI, SETO YUSUKE, NAGAI TAKAYA, LANGENHORST FALKO

  高圧討論会講演要旨集  2006/10
• Fe₃Cの高温高圧下での安定性  [Not invited]

  NAGAI TAKAYA, SETO YUSUKE, HAMANE DAISUKE, FUJINO KIYOSHI, SATA NAGAYOSHI

  高圧討論会講演要旨集  2006/10
• ガス駆動DACを使った放射光施設でのレーザー加熱実験  [Not invited]

  NAGAI TAKAYA, SATA NAGAYOSHI, OISHI YASUO, HAMANE DAISUKE, SETO YUSUKE, FUJINO KIYOSHI

  高圧討論会講演要旨集  2005/10
• MgSiO₃ perovskiteへのFe³⁺AlO₃成分の固溶  [Not invited]

  NISHIO DAISUKE, NAGAI TAKAYA, FUJINO KIYOSHI, SETO YUSUKE, TAKAFUJI NAOHITO

  日本鉱物学会年会・日本岩石鉱物鉱床学会学術講演会講演要旨集  2005/09
• コア‐マントル境界条件でのマグネサイトと鉄の反応  [Not invited]

  NAGAI TAKAYA, TAKAFUJI NAOHITO, SETO YUSUKE, HAMANE DAISUKE, FUJINO KIYOSHI, SATA NAGAYOSHI

  日本鉱物学会年会・日本岩石鉱物鉱床学会学術講演会講演要旨集  2005/09
• パルス中性子源を活用した量子機能発現機構に関する融合研究 高圧下における含水アルミニウム鉱物の構造と水素結合

  小松一生, 鍵裕之, 永井隆哉, PARISE John B., LOVEDAY John S.

  KEK Proceedings  2005
• FeAlO₃の高温高圧下での相転移  [Not invited]

  NAGAI TAKAYA, MIYAJIMA NOBUYOSHI, YAGI TAKEHIKO, YAMANAKA TAKAMITSU, FUJINO KIYOSHI

  高圧討論会講演要旨集  2004/09
• 下部マントル条件における(Mg,Fe)SiO₃‐Al₂O₃系での相関係およびペロブスカイト相へのFeとAlの固溶  [Not invited]

  NISHIO DAISUKE, FUJINO KIYOSHI, NAGAI TAKAYA, TAKAFUJI NAOTO

  日本鉱物学会年会・日本岩石鉱物鉱床学会学術講演会講演要旨集  2004
• FeAlO₃の高温高圧相変化  [Not invited]

  TANIMOTO TAKEHIKO, NAGAI TAKAYA, YAMANAKA TAKAMITSU, YAGI TAKEHIKO

  高圧討論会講演要旨集  2003/11
• Mn₂O₃の高圧構造解析と電荷移動による構造相転移  [Not invited]

  YAMANAKA TAKAMITSU, NAGAI TAKAYA, FUKUDA TOMOO, KITTAKA KOICHI

  高圧討論会講演要旨集  2003/11
• Fe_3-xTi_xO₄の高圧下での電気伝導度測定  [Not invited]

  MASUDA TOMOYUKI, YAMANAKA TAKAMITSU, NAGAI TAKAYA, SAKAMOTO DAISUKE

  高圧討論会講演要旨集  2003/11
• 遷移金属元素を含むイルメナイト型酸化物の圧縮挙動  [Not invited]

  NAGAI TAKAYA, TANIMOTO TAKEHIKO, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  2003/11
• Mn₂O₃の高圧単結晶構造解析と圧力相転移,電荷移動  [Not invited]

  YAMANAKA TAKAMITSU, NAGAI TAKAYA, FUKUDA TOMOO, KITTAKA KOICHI

  日本岩石鉱物鉱床学会学術講演会講演要旨集  2003/09
• 水素結合もった鉱物の圧縮挙動について‐NaHCO₃編‐  [Not invited]

  NAGAI TAKAYA, KAGI HIROYUKI, YAMANAKA TAKAMITSU

  日本岩石鉱物鉱床学会学術講演会講演要旨集  2003/09
• Kalicinite(KHCO₃)の圧力誘起相転移と水素結合  [Not invited]

  NAGAI TAKAYA, KAGI HIROYUKI, PARISE J B, LOVEDAY J S, YAMANAKA TAKAMITSU

  日本岩石鉱物鉱床学会学術講演会講演要旨集  2001/09
• Ca(OH)₂ Portlanditeの高温条件下での圧縮挙動  [Not invited]

  FUKUI HIROSHI, OTAKA OSAMU, NAGAI TAKAYA, KIKEGAWA TAKUMI

  日本鉱物学会年会講演要旨集  2000/11
• 放射光を用いたX線回折法による高圧下における結晶構造の精密決定  [Not invited]

  HATTORI TAKANORI, FUKUDA TOMOO, KITTAKA KOICHI, NAGAI TAKAYA, YAMANAKA TAKAMITSU

  日本鉱物学会年会講演要旨集  2000/11
• 石英‐コーサイト高圧相転移における相転移過程の観察と速度論  [Not invited]

  FUJISAWA TOMOYUKI, NAGAI TAKAYA, OTAKA OSAMU, YAMANAKA TAKAMITSU, UTSUMI WATARU

  日本鉱物学会年会講演要旨集  2000/11
• Athemal phase transformations of germanate pyroxenes under high-pressure condition.  [Not invited]

  HATTORI TAKANORI, NAGAI TAKAYA, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  2000/10
• In situ X-ray powder diffraction measurement under high pressure and high temperature using an external heated DAC in laboratory.  [Not invited]

  KITTAKA KOICHI, NAGAI TAKAYA, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  2000/10
• Compression mechanism of .ALPHA.-Mn2O3.  [Not invited]

  FUKUDA TOMOO, NAGAI TAKAYA, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  1999/11
• Variation of structure of Co(OH)2 under high pressure by powder X-ray diffraction.  [Not invited]

  KITTAKA KOICHI, NAGAI TAKAYA, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  1999/11
• Compressional study of FeTiO3 ilmenite .Trial for the single crystal structure analysis under high pressure by using DAC with stainless steel backing plate.  [Not invited]

  HATTORI TAKANORI, FUKUDA TOMOO, NAGAI TAKAYA, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  1999/11
• A pressure-induced phase transition of Mn2O3.  [Not invited]

  NAGAI TAKAYA, FUKUDA TOMOO, HATTORI TAKANORI, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  1999/11
• In situ synchrotron X-ray diffraction experiments at high pressure and high temperature using an external heated DAC.  [Not invited]

  NAGAI TAKAYA, KITTAKA KOICHI, HATTORI TAKANORI, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  1999/11
• FeTiO₃ilmeniteの圧縮機構 40GPaの高圧下での単結晶構造解析の試み  [Not invited]

  HATTORI TAKANORI, FUKUDA TOMOO, NAGAI TAKAYA, YAMANAKA TAKAMITSU

  日本岩石鉱物鉱床学会学術講演会講演要旨集  1999/09
• Ca(OH)₂高圧相の構造  [Not invited]

  FUKUI HIROSHI, OTAKA OSAMU, KUNISADA TAICHI, NAGAI TAKAYA, KIKEGAWA TAKUMI

  日本岩石鉱物鉱床学会学術講演会講演要旨集  1999/09
• 近赤外‐赤外分光法によるポートランダイトのOH振動の非調和性の圧力依存性  [Not invited]

  SHINODA KEIJI, NAGAI TAKAYA, AIKAWA NOBUYUKI

  日本岩石鉱物鉱床学会学術講演会講演要旨集  1999/09
• 外熱式ダイヤモンドアンビルセルによる高温高圧実験 下部マントルを目指して  [Not invited]

  NAGAI TAKAYA, KITTAKA KOICHI, HATTORI TAKANORI, YAMANAKA TAKAMITSU

  日本岩石鉱物鉱床学会学術講演会講演要旨集  1999/09
• X線その場観察によるMn₂O₃の高圧相転移の研究  [Not invited]

  NAGAI TAKAYA, FUKUDA TOMOO, HATTORI TAKANORI, YAMANAKA TAKAMITSU

  日本岩石鉱物鉱床学会学術講演会講演要旨集  1999/09
• The compression mechanism of FeGeO3high-P clinopyroxene.  [Not invited]

  HATTORI TAKANORI, NAGAI TAKAYA, YAMANAKA TAKAMITSU, WERNER S, SCHLUZ H

  高圧討論会講演要旨集  1998/11
• Compression mechanism of Mg(OH)2and Ca(OH)2.  [Not invited]

  NAGAI TAKAYA, HATTORI TAKANORI, TSUCHIYA TAKU, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  1998/11
• Phase transition of Ca(OH)2 portlandite under high temperature and pressure.  [Not invited]

  FUKUI HIROSHI, OTAKA OSAMU, NAGAI TAKAYA, KATSURA TOMOO

  日本岩石鉱物鉱床学会学術講演会講演要旨集  1998/10
• Kinetics of quartz-coesite transition using single crystal.  [Not invited]

  NAGAI TAKAYA, FUJISAWA TOMOYUKI, YAMANAKA TAKAMITSU

  日本岩石鉱物鉱床学会学術講演会講演要旨集  1998/10
• Dehydration of portlandite(Ca(OH)2) at high pressures.  [Not invited]

  FUKUI HIROYUKI, OTAKA OSAMU, MATSUOKA YOSHIHIRO, NAGAI TAKAYA, KATSURA TOMOO

  地球惑星科学関連学会合同大会予稿集  1998/05
• Clinopyroxene-Perovskite phase transition of FeGeO3 under high pressure and room temperature.  [Not invited]

  HATTORI TAKANORI, MATSUDA TADASHI, TSUCHIYA TAKU, NAGAI TAKAYA, YAMANAKA TAKAMITSU

  地球惑星科学関連学会合同大会予稿集  1998/05
• Change of potential between effective two bodies by pressure induced phase transition of KBr.  [Not invited]

  YOSHIASA AKIRA, MURAI KEIICHIRO, NAGAI TAKAYA, KAMISHIMA OSAMU, SHIMOMURA OSAMU

  日本鉱物学会年会講演要旨集  1997/09
• Monoclinic pyroxene - perovskite phase transition in high-pressure metastable state of FeGeO3.  [Not invited]

  HATTORI TAKANORI, MATSUDA TADASHI, NAGAI TAKAYA, YAMANAKA TAKAMITSU

  日本鉱物学会年会講演要旨集  1997/09
• Infrared absorption spectrum of portlandite under high-pressure.  [Not invited]

  SHINODA KEIJI, NAGAI TAKAYA, AIKAWA NOBUYUKI

  日本鉱物学会年会講演要旨集  1997/09
• Kinetics of rutile type .RAR..ALPHA.-PbO2 type phase transition of PbO2.  [Not invited]

  NAGAI TAKAYA, MATSUDA TADASHI, YAMANAKA TAKAMITSU

  日本鉱物学会年会講演要旨集  1997/09
• Structual phase transformation of FeGeO3 under high-pressure metastable condition.  [Not invited]

  HATTORI TAKANORI, NAGAI TAKAYA, YAMANAKA TAKAMITSU

  地球惑星科学関連学会合同大会予稿集  1997/03
• Kinetic studies of pressure-induced phase transformations.  [Not invited]

  NAGAI TAKAYA, OTAKA OSAMU, MATSUMOTO YOSHIHISA, MATSUDA ITARU, YAMANAKA TAKAMITSU

  地球内部物質の形成過程及び相変態のダイナミックス 平成7-8年度 No.07304073  1997
• In situ Observation of High Pressure and Temperature Phases of ZrO2.  [Not invited]

  OTAKA OSAMU, MATSUMOTO YOSHIHISA, NAGAI TAKAYA, YAMANAKA TAKAMITSU, KIKEGAWA TAKUMI, SHIMOMURA OSAMU

  高圧討論会講演要旨集  1996/11
• Comprehension of lattice instability under compression.  [Not invited]

  YAMANAKA TAKAMITSU, NAGAI TAKAYA, OTAKA OSAMU

  高圧討論会講演要旨集  1996/11
• EXAFS study on the effective anharmonic pair potentials under high pressure.  [Not invited]

  YOSHIASA AKIRA, NAGAI TAKAYA, NAKATSUKA AKIHIKO, OTAKA OSAMU, YAMANAKA TAKAMITSU, SHIMOMURA OSAMU, MAEDA HIRONOBU

  高圧討論会講演要旨集  1996/11
• Kinetic studies of phase transformations.  [Not invited]

  NAGAI TAKAYA, OTAKA OSAMU, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  1996/11
• Pressure induced phase transition of CuGeO3 ( chain structure ).  [Not invited]

  YAGYU GENTA, NAGAI TAKAYA, YAMANAKA TAKAMITSU, JAYARAMAN A, MING L C

  日本鉱物学会年会講演要旨集  1996/06
• Kinetics of the high pressure phase transition of PbO2.  [Not invited]

  MATSUDA TADASHI, YAMANAKA TAKAMITSU, NAGAI TAKAYA, HATTORI TAKANORI

  日本鉱物学会年会講演要旨集  1996/06
• Kinetics of the transition of quartz to coesite .  [Not invited]

  NAGAI TAKAYA, OTAKA OSAMU, YAMANAKA TAKAMITSU

  日本鉱物学会年会講演要旨集  1996/06
• TIME RESOLVED DIFFRACTION STUDY UNDER EXTREME CONDITION.  [Not invited]

  T. Yamanaka, T. Nagai

  ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES  1996  INT UNION CRYSTALLOGRAPHY
  
• In situ Observation of High Pressure and Temperature Phases of ZrO2.  [Not invited]

  OTAKA OSAMU, NAGAI TAKAYA, YAMANAKA TAKAMITSU, YAGI TAKEHIKO, SHIMOMURA OSAMU

  高圧討論会講演要旨集  1995/11
• XAFS measurements under high pressure and high temperature.  [Not invited]

  NAGAI TAKAYA, YOSHIASA AKIRA, OTAKA OSAMU, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  1995/11
• Crystallite strain and size analysis of the pressure-induced profile change.  [Not invited]

  YAMANAKA TAKAMITSU, NAGAI TAKAYA, OTAKA OSAMU

  高圧討論会講演要旨集  1995/11
• エネルギー分散プロファイルの圧力変化 粒径分布‐格子歪効果  [Not invited]

  山中高光, 永井隆哉

  日本結晶学会年会講演要旨集  1995/10  The Crystallographic Society of Japan
  
• Measurement of Debye-Waller factor of Ge by high pressure and temperature EXAFS.  [Not invited]

  YOSHITOMO AKIRA, NAGAI TAKAYA, OTAKA OSAMU, NAKATSUKA AKIHIKO, YAMANAKA TAKAMITSU, SHIMOMURA OSAMU, MAEDA HIRONOBU, ISHII TADAO

  日本結晶学会年会講演要旨集  1995/10  The Crystallographic Society of Japan
  
• ジルコニア高温高圧相のその場観察  [Not invited]

  大高理, 永井隆哉, 中塚晃彦, 山中高光, 下村理

  日本鉱物学会年会講演要旨集  1995/05
• Fe₃O₄‐γFe₂O₄系固溶体の高圧相平衡実験  [Not invited]

  藤部秀樹, 大高理, 永井隆哉, 山中高光

  日本鉱物学会年会講演要旨集  1995/05
• CaGeO₃の高温高圧下でのXAFS  [Not invited]

  永井隆哉, 大高理, 吉朝朗, 山中高光, 下村理

  日本鉱物学会年会講演要旨集  1995/05
• Tiem-resolved diffraction study with mili- or micro-second resolution applied for dehydration kinetics of minerals.  [Not invited]

  YAMANAKA TAKAMITSU, YOSHIASA AKIRA, OTAKA OSAMU, NAGAI TAKAYA

  地球惑星科学関連学会合同大会予稿集  1995/03
• High pressure synthesis of .GAMMA.-Fe2SiO4-Fe3O4 solid solution.  [Not invited]

  TOBE HIDEKI, OTAKA OSAMU, NAGAI TAKAYA, YAMANAKA TAKAMITSU, ITO EIJI

  高圧討論会講演要旨集  1994/11
• Mechanism of a high-density amorphous phase transition under high pressure.  [Not invited]

  YAMANAKA TAKAMITSU, NAGAI TAKAYA

  日本結晶学会年会講演要旨集  1994/11  The Crystallographic Society of Japan
  
• Pressure-induced Amorphization and Deep-Forcus Earthquakes.  [Not invited]

  NAGAI TAKAYA, YAMANAKA TAKAMITSU

  高圧討論会講演要旨集  1994/11
• CaGeO₃,MgGeO₃,Mg₂GeO₄の室温高圧下における構造変化について  [Not invited]

  永井隆哉, 山中高光

  日本鉱物学会年会講演要旨集  1994/06
• The Possibility of Pressure-induced Amorphization of CaGeO3.  [Not invited]

  永井隆哉, 大高理, 山中高光, 伊藤英司

  高圧討論会講演要旨集  1993/11
• CaGeO₃の圧力誘起非晶質化の可能性  [Not invited]

  永井隆哉, 大高理, 山中高光, 伊藤英司

  日本鉱物学会年会講演要旨集  1993/06
• 変動荷重下におけるフォルステライト単結晶の高温変形実験 転位組織について  [Not invited]

  永井隆哉, 鳥海光弘, 庄次正安

  日本鉱物学会年会講演要旨集  1992/05

MISC

• Aragonite表面における2価陽イオンの安定性:第一原理計算による考察

  KAWANO JUN, SAKUMA HIROSHI, NAGAI TAKAYA  日本地球化学会年会講演要旨集  60th-  253  2013  [Not refereed][Not invited]
  

Awards & Honors

• 2009 日本鉱物科学会論文賞
  
• 1998 日本鉱物学会論文賞
   

  受賞者: 永井隆哉

Research Grants & Projects

• Coordination and research support of the project "Earth Science Based on High-Pressure and High-Temperature Neutron Experiments

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

  Date (from‐to) : 2008/11 -2014/03 

  Author : YAGI Takehiko, UTSUMI Wataru

   

  本研究は平成20年度から24年度まで5年間にわたり行われた新学術領域研究「高温高圧中性子実験で拓く地球の物質科学」の総括と支援を行うために実施されたものである。新学術領域研究では東海村のJ-PARCに高圧中性子実験に特化した新しいビームライン、”PLANET”を建設し、それを用いて地球深部物質に対する高圧下の中性子回折実験を行い、特に水が及ぼす影響に着目して地球深部構造の研究を展開することを目的とした。そこで、予定通り建設されたPLANETを使ってさまざまな成果が出始めたことを踏まえ、それらを総括してさらなる発展の方向性を議論することや、新しい装置にが今後広い学問分野での研究に使われるようさまざまな広報活動を行うことが、本研究の目的となった。その方針に従い、さまざまな研究会を開催したり、国際会議で報告するために人を派遣したり、報告書やパンフレット等を作成した。
• Incorporation mechanism of hydrogen into some minerals and its dynamical behavior at high pressure

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

  Date (from‐to) : 2008 -2012 

  Author : NAGAI Takaya, AKASAKA Masahide, KURIBAYASHI Takahiro, NFUKAZAWA Hiroshi, SANO Asami, UTSUMI Wataru

   

  More and more application of neutron diffraction technique is expected in the field of mineral physics in the near future. Crystallographic information about hydrogen positions in some important hydrous minerals was successfully obtained in quite wide range of pressure-temperature conditions. These could give some new insights of hydrogen positions in some mantle minerals, a pressure-induced hydrogen-bond symmetrization mechanism, the relationship between specific thermal expansion and dynamical behavior of hydrogen atoms, and the relationship between cationic substitution and hydrogen positions in some crustal minerals.
• Spin transition of ferric iron in the lower mantle

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

  Date (from‐to) : 2009 -2011 

  Author : FUJINO Kiyoshi, NAGAI Takaya

   

  Spin transitions of ferric iron in Mg-perovskite(Pv) and post-Mg-perovskite(PPv) were examined up to 200 GPa and 165 GPa, respectively, by X-ray emission spectroscopy and X-ray diffraction. The results showed that high spin ferric iron in Pv moves from the A-site to the B-site above 50-60 GPa and becomes low spin, while ferric iron in PPv occupies the B-site and is low spin in its whole stability region.
• Origin of diamonds derived from the Earth's lower mantle

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

  Date (from‐to) : 2006 -2008 

  Author : NAGAI Takaya, KAGI Hiroyuki, SATA Nagayoshi, FUJINO Kiyoshi

   

  人類を魅了してやまないダイヤモンド。その中で近年多く認識されるようになった地下670km以深の下部マントルと呼ばれる領域を起源とするダイヤモンドは、炭酸塩鉱物が石英と一緒に地球深部の下部マントル中心部にまで沈み込んだときに生成された可能性があることを実験的に初めて明らかにした。このことは炭酸塩鉱物という地球表層に存在する鉱物が、地球深部に取り込まれる地質学的プロセスが存在し、さらに、生成したダイヤモンドが再び地球上にもたらされるというダイナミックな炭素循環が地球に存在することを意味する。
• パルス中性子線源を用いた高圧下中性子回折実験と鉱物科学の新展開

  日本学術振興会：科学研究費助成事業 基盤研究(C)

  Date (from‐to) : 2006 -2006 

  Author : 鍵 裕之, 永井 隆哉, 大高 理, 亀卦川 卓美, 近藤 忠, 高橋 博樹

   

  本研究では、東海村に建設中のパルス中性子線源J-PARCに、超高圧高温物質科学ビームラインを立ち上げるための準備作業を行うことを目的としている。鉱物物理、結晶学、材料科学などの分野の研究者総勢31名がメンバーとして加わり、今後のサイエンスの動向や、必要とされるビームラインの性能などについて議論を重ねた。2006年5月のキックオフミーティングを皮切りに、ほぼ2ヶ月に一度の割合でメンバーを集め、テクニカルミーティングを開いた。特筆すべきものとして、10月24日、25日の2日間にわたって、物性研究所短期研究会として本科研費での研究課題について、60名ほどの聴衆を集めて活発な討論を行うことができた。 このような流れを受けて、高圧ビームラインの建設を目指した特定領域研究「中性子で拓く地球と惑星の高圧物質科学」(領域代表:八木健彦東大物性研教授)と、超高圧条件に特化した中性子回折測定技術の開発を目指した学術創成研究「強力パルス中性子線源を活用した超高圧物質科学の開拓」(研究代表者:鍵 裕之)を本科研費メンバーが中核となって申請することができた。残念ながら特定領域研究はいま一歩のところで採択されなかったが、学術創成研究は5年計画で採択され、現在は中性子のビーム集光技術の開発や、新しい大容量高圧プレスの開発研究を進めている。 本企画調査研究は次の大きなステップにつながり、成功裏に終了したと自他共に評価できるものとなった。今後はビームライン建設のための大型予算の獲得へ向けて、メンバー一同さらなる努力を重ねる予定である。
• Development of simultaneous measurements system of electric conductivity and x-ray diffraction on mantle minerals at high pressure and temperature

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

  Date (from‐to) : 2003 -2004 

  Author : NAGAI Takaya

   

  A diamond anvil cell, which can apply to electric resistance and x-ray diffraction measurements simultaneously, was designed in this research project. The DAC is basically modified the lever & spring type DAC and two electrodes model for electric resistance measurements is installed the DAC. A series of single crystals of the magnetite (Fe_3O_4)-ulvospinel (Fe_2TiO_4) solid solution were synthesized by the FZ method. Then, electric resistance measurements were performed on those samples and x-ray diffraction measurements were also performed at the same time. Electric resistances on all samples decrease gradually with increasing pressure probably due to the electron hopping and the band overlapping mechanism. However, the electric resistances suddenly show no pressure-dependency-above some critical pressures. The critical pressure increases with iron content in the solid solution of Fe_<3-x>Ti_xO_4. For example, the critical pressures are about 6.5GPa for Fe_2TiO_4 and about 24GPa for Fe_3O_4. X-ray powder diffraction patterns obtained above the critical pressure showed that some single diffraction peaks split into doublet peaks above the critical pressure. The evidence suggests a structural transition occurs at the critical pressure. According to the single crystal structure analysis experiments on Fe_2TiO_4 at high pressure, the structural transition could be assigned as the transition from cubic to tetragonal symmetry and the Mn_3O_4 type structure can be proposed as a candidate of the high-pressure form of Fe_2TiO_4. The newly designed system in this research project can provide some interesting and important information about the relationship between the crystal structures and electric resistances.
• Lattice dynamics study of pressure-induced structure change of earth materials under high pressure using single crystals.

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

  Date (from‐to) : 2002 -2004 

  Author : YAMANAKA Takamitsu, OHTAKA Osamu, OKADA Taku

   

  For the investigation of earth interiors under high-temperature and high-pressure condition of the mantle, lattice dynamical studies under high pressures are complementary with X-ray diffraction structure analyses using single crystals. By means of the latter experiments, the crystal structure information can be provided from the interatomic distances, bonding electron, effective charge and electronic state. In formation of interatomic force can be provided from lattice dynamical analysis. The present experiment aims to elucidate crystal dynamical charge as functions of temperature and pressure by means of laser Raman spectroscopy. (1)At the first stage of this experiment during these three years(2002-2004) with the aid of the Scientific Research (A)(2)development and test of the microscopic Raman spectrometer have been made under extreme conditions. (2)The new lattice dynamical experimental system has been performed for the purpose that Raman spectral studies taking into account the crystallographic anisotropy have been executed using single crystal. (3)In order to comprehend the phase transformation of MgSiO3 polymorphs in mantle, pyroxene-garnet-ilmenite-perovskite, three synthetic ilmenites, MgSiO3 MgGeO3and MgTiO3, are applied for the measuring Raman shift with compositional effect. (4)Pressure effect of these three ilmenites has been clarified as a function of pressure using diamond anvil pressure cell (DAC), in which powder sample and transmitting media are installed. (5)For the purpose of understanding the water presence in the mantle, kinetic studies of Raman spectra of hydrous silicate minerals have been conducted. From the investigation of pressure effect of hydrogen bond O-H…O, bulk modulus, elastic properties and equation of state have been discussed for pressure-induced transformation. (6)Pressure effect of the electron density distribution, lattice distortion and charge transfer were investigated using synchrotron radiation from the viewpoint of solid-state electron. Phase stability of earth's interiors has been discussed from the Raman spectroscopic analyses together with the above-mentioned X-ray diffraction studies.
• Crystal structure refinement of mantle minerals under high pressure and temperature using Rietveld method

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

  Date (from‐to) : 2001 -2002 

  Author : NAGAI Takaya

   

  In-situ X-ray diffraction measurements under pressure were performed on several minerals and obtained powder diffraction patterns were analyzed by means of Rietveld structure refinement method. High pressure is generated by a diamond anvil cell (DAC) and X-ray diffraction experiments were mainly performed in synchrotron radiation facilities, such as PF and SPring8. Shortening of hydrogen bonded oxygen-oxygen distances controls compression of some hydrous minerals, such as KHCO_3 and NaHCO_3. A phase transition occurs on KHCO_3 at about 2.8 Gpa. It is interesting thai hydrogen bonded O-O distance in NaHCO_3 reaches to 2.4 A^^○ at 9 Gpa and this suggests a possibility of hydrogen bond symmetrization. Shortening of hydrogen bonded O-O distance also controls compression behavior of goethite and its shortening behavior is quite similar to that of ice VII. Laser annealing is quile useful for relaxing strain in materials caused by nonhydrostatic pressure Laser annealing was applied to compression experiments of NiTiO_3-ilmenite in PF. Obtained diffraction patterns after annealing treatment were greatly improved and Rietveld analysis could be done successfully up to 20 Gpa. Laser heating is a powerful method for creating lower mantle conditions on the earth. We performed insitu X-ray diffraction experiments under high pressure and temperature conditions at SPnng8 to clarify a possibility of a reaction between maguesite and iron. No evidence of the reaction was observed at 2000℃ and 1000℃ at 40 Gpa Diffraction patterns of CaSiO_3 perovskite could be observed at 20 Gpa and 1500-1600 K. Technical improvements are still needed but quite good quality diffraction patterns were recorded. EOS of CaO was determined by X-ray diffraction measurements using a hydraulically operated DAC and discusses a possibility of dissociation reaction of CaSiO_3 perovskile at the lowest part of the lower mantle.
• Crystal structure and solid state physics of earth's interiors under high pressure and high temperature

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

  Date (from‐to) : 1999 -2000 

  Author : YAMANAKA Takamitsu, NAGAI Takaya, OHTAKA Osamu, YOSHIASA Akira, SHIMOMURA Osamu, YAGI Takehiko

   

  In order to understand dynamics of mantle or earth's shell, such as subduction of slab, mechanism of deep earthquake and mantle convection, in situ investigations of material sciences of constituent substances under high pressure and temperature are significant subject. Present experimental proposal is the collaboration works between French and Japanese geophysicists with mutual relations. By making use of the facilities in ESRF in Francc and SPring-8 and Photon Factory, phase transitions of oxides and silicates was studied under compression or stress field. Studies of solid state physics of electric conductivity, conductivity, elastic coefficient and thermal expansion coefficient were made using diamond anvil or multianvil high-pressure apparatus. The following experiments were executed : Electric conductivity measurement of olivine (Mg1-x, Fex)2SiO4 under high pressure and high temperature was carried out by using multianvil high-pressure apparatus. Thc measurement was conducted at temperature up to 1000 and pressure up to 6GPa. Geothermal change with depth can be estimated from the experimental results The electric conductivity measurement of Fe2SiO4 indicate a large gap of the conductivity at the olivine-spinel transition at about 6GPa. It is clarified that the carrier of the conduction is attributed to the Fe^<2+>⇔Fe^<3+> electron hopping rather than hole. ÅiCRÅjBy using diamond anvil high-pressure cell, electric conductivity of wustite (Mg1-x, Fex)O, one of major lower mantle substance, was measured measurement as functions of pressure and temperature together with Fe composition (x=0.1, 0.3, 0.5). This experiment was carried out at Inst. Physque du Globe, ) Paris University. Activation energy of electric conductivity was elucidated. With increasing Fe content in the solid solution the conductivity is elevated. The d-electron configuration of Fe ion in the bonding electron raises the conductivity. ÅiCSÅjCollaboration work with Prof.J.P.Poirier (Inst.Physque du Globe) is the investigation of the melting curve of iron metal, earth core material at extremely high temperature over 2000℃ under high pressure.The experiment was made with the multianvil apparatus and synchrotron radiation at SPring-8. For this experiment The present Grant-in-Aid supported the travel fee of Dr.Andrault. Dr.Ohtaka of Osaka University and Dr.Shimomura of SPring-8 stuff were supporting members. All experimental results have been reported at several International Conference or workshop and they were published in the science journals.
• Lattice instability and kinetic study of mantle substances in the nonequilibrium process under high-pressure and high stress field

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

  Date (from‐to) : 1998 -2000 

  Author : YAMANAKA Takamitsu, NAGAI Takaya, OHTAKA Osamu, YOSHIASA Akira

   

  Structure changes of EarthAfs interiors under compression, such as phase transformation, decomposition, amorphization or solid reactions have been discussed by the lattice instability due to the plastic and elastic deformation. Their athermal structure changes become more crucial problems in order to elucidate geophysical dynamical process. In situ pressure-induced structure changes have been investigated by synchrotron radiation. Anisotropic structures such as chain structure or layered structures like pyroxene and olivine are subjected to a large effect of the shear stress in the mantle. Nonhydrostatic condition gave an anisotropic lattice deformation, which is different from those hydrostatic compression. The following experimental results have been published in science jourals and reported at international conference or domestic science anual meetings : (1) At kinetically low temperatures atomic mobility is not large enough to generate thermodynamically stable phases. The phase transition is possible by the non-diffusion martensic transformation or small atomic displacement under stress field. FeGeO3 clinopyroxene showed a reversible transformation to high-pressure phase (pseudo ilmenite) under hydrostatic condition, which was newly found. Then it transforms to ilmenite and further perovskite structure. This transition path was firstly found. (2) The structure changes are resulted from the elastic transformation mainly due to the virial theorem between external pressure and interatomic forces. Electron density measurement of SiO2 stishovite under high pressures up to 50GPa was clarified by using the newly devised diamond anvil and synchrotron radiation. Through single-crystal structure analysis the bonding electron density changes with pressure was confirmed. (3) Kinetic study of quartz-coesite transition was carried out by time-resolved diffraction experiment using multianvil high-pressure apparatus at SPring-8. Nucleation and growth were separately analyzed resulting in giving the transition rate and activation energy. It is clarified that the nucleation starts at the crystal surface or grain boundary. (4) Pressure-induced amorfization of hydrates were examined and two different types of the elastic and plastic deformation of lattice transition bring the amorfization. (5) MD calculation suggested that those phase transformations and their dynamical processes reflect the mechanism of elastic instability, which is a precursor atomic movement on the transition process. Some sublattices such as dense zone are preserved and the others are deformed in the random fashion. Elastic constants cij as a function of pressure calculated from MD reveal elastic instability in the course of structure transformation. The lattice instability can be interpreted by elastic tensors based on BomÅfs criterion. Under the condition that some elastic tensors or their combination become negative, structure becomes unstable resulting in the transformation. (6) Structure anisotropy brings the variation of metastable phases in the kinetics of phase transformation under pressure by OstwaldÅfs step rule. Then thermodynamically stable phases are not only candidates found in nature. Nonhydrostatic or quasihydrostatic condition brings metastable or intermediate phases in the proen of phase transition. (7) High-pressure EXAFS spectroscopy brought the local structure of solid ionics. Anharonic thermal effect on the pair potential of gold metal was observed by high-tcmperature and pressure study.
• Development of time resolved diffraction study under high pressure using charge coupled devise detector

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

  Date (from‐to) : 1998 -2000 

  Author : YAMANAKA Takamitsu, NAGAI Takaya, YOSHIASA Akira, TSUNEMI Hiroshi

   

  The aim of the present research project aimed to investigate the structure changes and stability relations of earth's interiors under the conditions of same temperature and pressure as carth mantle and core. Dynamical structure changes under compression were observed by time-resolved diffraction experiment in time interval of second or millisecond. In order to understand the mechanism of phase transition or decomposition, we developed the single-crystal X-ray diffraction system for kinetic studies of these structure transformations. For this purpose, two-dimensional X-ray detector of charge coupled detector (CCD) was planed to be installed in the newly devised system. It enables to execute the time-resolved study. After searching the several CCD detectors made by SIMENS, NONIUS, QUANTUM and RIGAKU.The RIGAKU detector was tested from the viewpoints of dynamic range, quantum efficiency, positional resolution and reproducibility. Computer programs for driving the system and data analysis were also developed. Combined with the rotating anode X-ray generator and HUBER four-circle diffractometer facilitated in laboratory, diamond anvil high-pressure cell with electric resistance heater makes possible the diffraction study of structure transformation in the process of compression. The high-pressure and high-temperature studies up to 80GPa and 550℃ can be possible. The present instrumental development has already been reported in annual meeting of High-Pressure Technology and Sciences : By using the new system the following experiments are scheduled in near future. (1) Observation of pressure-induced amorphization, martensic structure transition, and precursor phenomenon of melting. (2) Time-resolving diffraction study of structure transformation including dehydration, degas, phase decomposition, radiation damage etc. (3) Inspection of crystallization from melts. (4) Perception of solid-solid reaction under compression with heating condition. (5) Elucidation of electronic density of state in the filed of material sciences, metallurgy, solid-state physics and several other science. The present detector system combined with synchrotron radiation will be an effective tool for kinetic study of structure transformation.
• Effective factors in the kinetics of pressure-induced transformation.

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

  Date (from‐to) : 1998 -1999 

  Author : NAGAI Takaya

   

  The kinetics of the quartz-coesite transformation were investigated at 4 GPa and 650, 750 and 850℃ using quartz single crystal and powdered samples. Optical microscopic observations for partly transformed single crystal samples indicate that the coesite heterogeneously nucleates on the surface of the quartz grain and grows into the interior. The growth rate of coesite is independent of crystallographic orientations. The mechanism of incoherent grain-boundary nucleation and interface-controlled growth seems to operate during the transformation. The thickness of the coesite rims increases linearly as a function of time and the growth rate clearly depends on temperature. The activation energy for growth of coesite is determined as 85 (±11) kJ/mol and this value is significantly small in comparison with that determined for powdered samples. Synchrotron x-ray powder diffraction studies were performed on Ca(OH)ィイD22ィエD2 and Mg(OH)ィイD22ィエD2 under room temperature pressurization to 10.4 GPa and 16.0 GPa, respectively. We used the diamond anvil cells technique and the data were collected with an imaging plate detector at BL-18C in Photon Factory at KEK, Japan. The c-axis is much softer than the a-axis and, thus, the c/a ratio decreases with pressure. There is no remarkable discontinuity in the compression curves. The atomic position of O atoms, (1/3, 2/3, z), has been successfully refined using Rietveld analysis of x-ray powder diffraction patterns. In Mg(OH)ィイD22ィエD2, a change of compression mechanism is observed at 11GPa. However, in Ca(OH)ィイD22ィエD2, it is concluded that the shortening of the interlayer spacing controls compression below the amorphization pressure and no change of compression mechanism has occurred. It has been reported that H disorder occurs at a pressure in Mg(OH)ィイD22ィエD2 and the present results clearly suggest that the H disorder has great influence on the compression behavior.
• Structure & physical Properties of Earth Interior at High Pressure

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for international Scientific Research

  Date (from‐to) : 1996 -1997 

  Author : YAMANAKA Takamitsu, NAGAI Takaya, OTAKA Osamu, YOSHIASA Akira, YAGI Takehiko, SHIMOMURA Osamu

   

  In order to comprehend the dynamics of theology, earth quake and subduction of slab in the earth crust or mantle, we investigate the phase transition and structure change of earth materials under high temperature and pressure. We have also proceed the collaboration works concerning the solid state earth science and high pressure technology with German crystallographers and mineralogists using synchrotron and neutron diffraction. It has been known that structure and texture changes of minerals composed of polycrystalline materials under stress field induces the solid mobility. For the purpose of understanding the above mentioned mechanical process, quantitative kinetic investigations has been undertaken by the simulation of physco-chemical process found in the earth interiors as a function of temperature, pressure, partial pressure, electric field, magnetic field and chemical potential. Our investigations are worth while not only for science intelligence of material structure and texture under high pressure but also for the suggestions to the analysis of the mechanism of the earth crust dynamics and mantle science. The present research has provided the great influence to the collaboration between German and Japanese mineral science. The following research projects have been performed : (1) Structure change with ascent and descent of earth interiors (precise measurement of intracrystalline proliferation and computer simulation as a function of pressure-temperature-time.) (2) Analysis of plastic and elastic deformation of crystal lattice under high pressure and temperature. (3) Mobility of earth materials as functions of such deriving forces as bulk modulus, viscosity, thermal expansibity, elastic velocity.
• In situ observation and kinetics of the phase transformation under high pressure and stress

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

  Date (from‐to) : 1996 -1997 

  Author : YAMANAKA Takamitsu, NAGAI Takaya, OTAKA Osamu, UEDA Chiaki, YOSHIASA Akira

   

  Present investigation aims to discuss the kinetics of the phase transformation of silicates and hydrates constituting earth crust and mantle. It has been known that the phase change often stays in the metastable or even unstable state by the Ostwald step rule, when the thermal energy is not large enough to supply the proper activation energy for the phase transformation. For the purpose of understanding the above mentioned mechanical process, quantitative kinetic investigations have been undertaken by the simulation of physico-chemical process found in the earth interiors as a function of temperature, pressure and stress. The following research projects have been performed : (1) X-ray diffraction study of the phase transition of Ca(OH)2, which is an analog material to mafic hydrates such as serpentine, has been carried out using the single crystal under hydrostatic pressure condition at 300K with diamond-avil cell (DAC). The compression induced a high density amorphous state but never brought a CaCl2 type high pressure stable phase. This pressure-induced amorphization was caused by elastic deformation of the lattice and it is a reversible transformation. (2) An internal Pt heating system installed in the DAC enable to simulate the more precise phase transformation in the earth mantle in consideration of the geothermal gradient. Kinetics study of the structure change from quartz to coesite under various pressures and temperatures was undertakek by the time resolved diffraction study, Their physical properties such as thermal expansibity, bulk moduli and elastic constants were observed. It has clarified that the various compression paths and heating processes bring a different threshold transition critical pressure and temperature. (3) The present Raman spectroscopic study and EXAFS experiment accounts for the elastic or plastic lattice deformation causes the amorphization under high pressure. The investigation of the local structure of glass and high density amorphous phase of GeO2 could explain the different mechanism of the pressure-induced amorphization. (4) Simulation of structure change of SiO2, GeO2, SnO2 and PbO2 having a rutile structure has been executed under variable stress field through the molecular dynamical calculation using optimized pair potential and molecular orbital calculation based on DX-Xalpha method.
• ゲルマン酸塩の高圧相転移のMD法によるシミュレーションとX線その場観察実験

  日本学術振興会：科学研究費助成事業 奨励研究(A)

  Date (from‐to) : 1996 -1996 

  Author : 永井 隆哉

   

  本研究ではGeO_2とMgGeO_3に関して、分子動力学法(MD法)を用いた、高圧下での構造相転移について研究することを主目的とした。 原子間相互作用としてBorn-Mayer型のポテンシャルを採用した。パラメータは現在までに報告されている多形の結晶構造、体積弾性率を再現できるようにMD法によって決定した。計算にはプログラムWMIN、MXDTRICLを用いた。得られたパラメータは数%以下の誤差で構造、物性を再現でき、ゲルマン酸について初めての信頼できるパラメータである。このパラメータを用いて以下の構造相転移について検討した。 〈GeO_2〉圧力誘起非晶質化の機構の解明とポストルチル相の探索を行った。非晶質化は実験で知られている転移圧とほぼ同じ圧力で再現され、この転移がGeの配位数の4配位から6配位への変化を伴っていること、酸素の最密充填面がこの転移を通じて保持されていることが明かになった。ポストルチル相に関しては、室温下80GPaでCaCl_2型に相転移する可能性が示唆される結果を得た。このタイプの転移は、SiO_2(スティショバイト)のポストルチル転移の候補としても指摘されており、現在実験的な検証を進行中である。 〈MgGeO_3〉単斜輝石構造を出発構造とし、室温下での加圧による構造変化をMD法を用いて調べた。結果は、約10GPaでこれまでMgGeO_3で報告のないタイプの構造相転移が起こる可能性を示唆し、その転移がGeの配位数変化を伴うことを予測した。そこでダイヤモンドアンビルセルを使った高圧X線回折実験その場観察を行い検証を試みた。その結果、15〜23GPaで回折図形が変化することを見い出した。この変化は、圧力の絶対値は数GPaの不一致であるものの、これまでMgGeO_3の単斜輝石について報告されている構造相転移では説明できず、今回のMD法による予測と同一の構造相転移を観察した可能性がある。
• Evaporation Experiments on Planetary Materials.

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

  Date (from‐to) : 1995 -1996 

  Author : TSUCHIYAMA Akira, NAGAI Takaya, YAMANAKA Takamitsu, UYEDA Chiaki

   

  It has been believed that evaporation and condensation processes playd important roles in differentiation of materials during the formation of the solar system. The following results were obtained in the present project in relation to the above topics. (1) Experimental techniques for exactly obtaining time variation in the amounts of evaporation and condensation by using ultra-high temperature thermal balance to discuss their kinetics strictly were developed. First of all, dehydration experiments on hydrous silicate minerals and glass were carried out, and it was confirmed that kinetics of dehydration, wthich is regarded as incongruent evaporation of water, can be discussed by time variation in the amouts of dehydration. Evaporation experiments of alkalies (Na and K) on silicate melts were carried out at low pressures, and the evaporation rates were successfully obtained. (2) A new model on evaporation of Na from silicate melts and origin of chondrules was proposed. It was shown that chondrule formation is possible not only by open-system flash heating mechanism which has been proposed previously but by closed-system gradual heating. This gave a new viewpoint on the chondrule formation issue. (3) Evaporation experiments on Fe-S minerals (metallic iron and troilite) were done, and their kinetics (modes and rates) were obtained. Evaporation rates of these minerals in the primordial solar nebula were estimated based on the present results, and the Fe/S fractionation in the primordial solar nebula was discussed by combining a model for formation of a protoplanetary disk with the evaporation data.
• 層状含水鉱物の脱水反応のカイネティクスに及ぼす圧力効果

  日本学術振興会：科学研究費助成事業 奨励研究(A)

  Date (from‐to) : 1995 -1995 

  Author : 永井 隆哉

   

  本研究では、抵抗加熱方式による高温DACの開発と高エネルギー物理学研究所における放射光X線を使った層状含水鉱物の脱水反応のカイネティクスに及ぼす圧力効果を見積もるための予備実験を遂行した。 高温用ダイヤモンドアンビルセル(高温DAC)は、0.3mm径のニクロム線をコイル状に巻いたものをダイヤモンドアンビルの周囲に置き、その周囲に断熱のためのマイカやパイロフィライトで覆うことで、125Wの電力の投入により試料部で10GPa、約400°Cまでの加熱が達成された。目標である500〜800°Cの達成には2段階加熱方式の採用やダイヤモンドのダメ-ジを軽減させるための対策などさらなる改良が必要であり現在進行中である。またこの高温DACを回転対陰極X線発生装置と湾曲型位置敏感X線検出器のシステムに組み込み光軸を調整する機構を設計作成し、高温高圧下でのX線回折実験可能なシステムを完成させた。 高エネルギー物理学研究所においては、ARに設置されたMAX80システムを使った。実験はエネルギー分散法によった。まず時分割でのX線回折実験の予備実験としてSiO2の石英-コ-サイト転移のカイネティクスへの圧力効果を見積もる実験を行った。実験条件は3〜6GPa、600〜900°Cである。1分間隔での時分割測定が可能で、解析の結果圧力の増加は指数関数的に反応速度を速くする傾向にあることが明らかになった。つぎに行った層状含水鉱物の脱水反応では、高圧下で1000°C以上の高温になってしまうことがわかり、これまでの高圧セル構成では実験が不可能であるた。そこでグラファイトの環状ヒーターを使うなどのセルの改良を試みた。その結果、6GPa、1300°C程度までの実験が可能になり、ブルーサイトMg(OH)2について3GPaでの脱水反応が確認できた。
• Evaporation Experiments on Planetary Materials.

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

  Date (from‐to) : 1993 -1994 

  Author : TSUCHIYAMA Akira, NAGAI Takaya, TAKUBO Hiroshi, YAMANAKA Takamitsu, MATSUDA Junichi, UEDA Chiaki

   

  Evaporation rates and their evaporation coefficients of important minerals forming terrestrial planets (forsterite, metallic iron, and troilite) were determined by evaporation experiments. Forsterite evaporates congruently, and the evaporation obeys a linear rate law. Its evaporation coefficient showed that the evaporation of forsterite under a H_2-rich atmosphere occurs by mechanism similar to that of free evaporation. From the results, evaporation rates of forsterite in a primordial solar nebula can be estimated. Evaporation of metallic iron also obeys a linear rate law, and its evaporation coefficient is close to unity. Incongruent evaporation of troilite with metallic iron residue obeys a linear rate law due to reaction at the troilite-metallic iron interface as a rate-determining process. From the experimental results together with previous data, evaporation rates of important minerals forming terrestrial planets were complied. Elemental fractionation (Mg/Si and Fe/S) due to evaporation of mineral dust in the primordial solar nebula was discussed based on the complied data. It was suggested that incongruent evaporation of enstatite did not occur but apparent congruent evaporation of enstatite occurred, and thus no Mg/Si fractionation is expected. However, Mg/Si fractionation is possible as long as the dust was amorphous Mg-silicate. Fe/S fractionation was expected due to incongruent evaporation of troilite. A model for isotopic mass fractionation due to evaporation of solids was also constructed based on the evaporation rates of the minerals. The fractionation depends on the evaporation rate, diffusion coefficient in the solid, the size of the solid, and isotopic fractionation factor which is determined from the mass of evaporated molecules. Based on the model, conditions for isotopic mass fractionation found in meteorites were estimated successfully.
• 珪酸塩鉱物の圧力誘起転移のカイネティクスと弾性波速度

  日本学術振興会：科学研究費助成事業 一般研究(C)

  Date (from‐to) : 1993 -1993 

  Author : 山中 高光, 永井 隆哉, 大高 理, 植田 千秋, 土山 明, 田窪 宏

   

  プレートの流動現象や、沈み込むスラブの運動を把握するためにはダイナミカルな構造研究をする上で、地殻やマントルの構成鉱物の環境変化(温度・圧力・成分等)に伴って、生じる転移・分解・融解・結晶内イオン交換反応等の諸々の構造変化のカイネティックスや機構を究明することが重要な課題である。本実験ではケイ酸塩鉱物や類似鉱物の圧力誘起による構造変化と逐次観察と動的構造の研究を行った。 1.マントルの主構成鉱物であるカンラン石(Mg_2SiO_4)について分子動力学(MD)計算を用いて圧力誘起の構造転移のシミュレーションを行った。室温では35〜40GPa圧力領域で圧力誘起非晶質相転移が生じ、95〜100GPaで未記載な結晶構造に再結晶化することが計算から明らかになった。ダイヤモンドアンビル高圧発生装置と放射光X線を用いた高圧実験でカンラン石のGe置換体のMg_2GeO_4の圧力誘起非晶質相転移を実際に確認した。 2.マフィックな珪酸塩鉱物が海洋地殻で水和物に変質し、それらがサブダクションでの低温(<500℃)で応力下での構造安定性を調べ水の挙動を研究する。そのためCa(OH)_2の圧力誘起相転移と準安定相の存在領域を放射光X線回折実験で決定しその機構を解明した。その結果水和鉱物は高圧下では脱水反応はせず、非晶質相として地殻内部にもたらされ、これらがマグマなどに重要な水の起源として考えられる。 3.マルチアンビル高圧発生装置に装着し、SiO_2の同一の多形構造転移を示すGeO_2の圧力誘起非晶質相転移した物質についてS波とP波の弾性波速度を測定し、体積圧縮率や剛性率を求めた。これらの弾性波速度の温度・圧力変化の研究はサブダクション・ゾーンで生じる深発地震の発生の解明にも貢献した。また分子動力学から求められた温度圧力関数にした弾性常数の変化と比較し検討した。

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• 2021年4月1日 

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  2023年3月31日 

  教育研究評議会評議員
• 2021年4月1日 

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  2023年3月31日 

  大学院理学院長
• 2019年4月1日 

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  2021年3月31日 

  大学院理学研究院副研究院長
• 2023年4月1日 

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  2025年3月31日 

  大学院理学院長