Takaya Nagai

Hokkaido University, Sapporo, Hokkaidō, Japan

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Publications (42)99.1 Total impact

  • Jun Kawano, Hiroshi Sakuma, Takaya Nagai
    12/2015; 2(1). DOI:10.1186/s40645-015-0039-4
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    ABSTRACT: 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.
    Journal of Solid State Chemistry 10/2014; 218:95–102. DOI:10.1016/j.jssc.2014.06.010
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    ABSTRACT: Spin transition and substitution of Fe3+ in Fe3+AlO3-bearing MgSiO3 perovskite (Pv) and post-perovskite (PPv) were examined up to 200 GPa 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.
    Physics of The Earth and Planetary Interiors 03/2014; 228. DOI:10.1016/j.pepi.2013.12.008
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    ABSTRACT: 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.
    Physics and Chemistry of Minerals 02/2014; 42(2). DOI:10.1007/s00269-014-0703-z
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    ABSTRACT: 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 $ \sqrt{2}\,a/c, $ 2 a / c , monotonically decreases from MgSiO3 to MnSiO3 perovskite at about 50 GPa. The orthorhombic distortion in (Mg0.5, Mn0.5)SiO3 perovskite is almost unchanged with increasing pressure from 30 to 50 GPa. On the other hand, that distortion in (Mg0.9, Mn0.1)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 (Mg0.9, Mn0.1)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.
    Physics and Chemistry of Minerals 07/2013; 41(6). DOI:10.1007/s00269-013-0618-0
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    ABSTRACT: 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 1-2μm 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 CaCO(3)-supersaturated state during fiber growth and that a physical change occurs periodically during the aragonite crystals of the fiber area.
    Journal of Structural Biology 10/2012; 180(3). DOI:10.1016/j.jsb.2012.09.009
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    ABSTRACT: 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 Mg0.85Fe3 +0.15Al0.15Si0.85O3 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 ~ 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 ~ 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 ~ 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.
    Earth and Planetary Science Letters 02/2012; s 317–318:407–412. DOI:10.1016/j.epsl.2011.12.006
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    ABSTRACT: 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 28.5GPa, 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. KeywordsPortlandite–Isotope effect–Phase transition–Hydrostaticity–Hydrogen bonding
    Physics and Chemistry of Minerals 12/2011; 38(10):777-785. DOI:10.1007/s00269-011-0450-3
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    ABSTRACT: The El Niño/Southern Oscillation (ENSO) system during the Pliocene warm period (PWP; 3-5 million years ago) may have existed in a permanent El Niño state with a sharply reduced zonal sea surface temperature (SST) gradient in the equatorial Pacific Ocean. 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, 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. Here we show that permanent El Niño conditions did not exist during the PWP. Our spectral analysis of the δ(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, δ(18)O anomalies from a nearby live Porites coral are correlated with modern records of ENSO variability. Second, negative-δ(18)O events in the fossil corals closely resemble the decreases in δ(18)O seen in the live coral during El Niño events. Prior research advocating a permanent El Niño 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.
    Nature 03/2011; 471(7337):209-11. DOI:10.1038/nature09777
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    ABSTRACT: 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.
    01/2011; 53(1):8-12. DOI:10.5940/jcrsj.53.8
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 03/2010; 31(13). DOI:10.1002/chin.200013007
  • The Review of High Pressure Science and Technology 01/2010; 20(3):269-276. DOI:10.4131/jshpreview.20.269
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    ABSTRACT: 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 CaIrO3-type post-perovskite structure even at the Earth's core–mantle boundary conditions, although CaSiO3 perovskite has a potentiality to transform to the CaIrO3-type post-perovskite structure at still higher pressure as long as another type of transformation does not occur.
    Physics of The Earth and Planetary Interiors 12/2009; 177(s 3–4):147–151. DOI:10.1016/j.pepi.2009.08.009
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    ABSTRACT: 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.
    American Mineralogist 08/2009; 94(8-9):1255-1261. DOI:10.2138/am.2009.3109
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    ABSTRACT: 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.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/2009; 600(1):50-52. DOI:10.1016/j.nima.2008.11.065
  • The Review of High Pressure Science and Technology 01/2009; 19(1):15-23. DOI:10.4131/jshpreview.19.15
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    ABSTRACT: 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 α -FeOOH at high pressure were measured using the KBr micro-pellet method with a helium pressure-transmitting medium. Downshift of the OH stretching vibration was observed with increasing pressure. Use of the KBr micro-pellet method for infrared absorption spectroscopy at high pressure is a complementary experimental technique to neutron diffraction at high pressure for studying the pressure response of hydrogen bonds.
    High Pressure Research 09/2008; 28(3):299-306. DOI:10.1080/08957950802346868
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    ABSTRACT: We report on high-pressure and high-temperature experiments involving carbonates and silicates at 30–80GPa and 1,600–3,200K, corresponding to depths within the Earth of approximately 800–2,200km. 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 200–300°C 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 70GPa, which might imply a possible mechanism for diamond formation in the lower mantle.
    Physics and Chemistry of Minerals 05/2008; 35(4):223-229. DOI:10.1007/s00269-008-0215-9
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    ABSTRACT: 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.
    American Mineralogist 04/2008; 93(4):653-657. DOI:10.2138/am.2008.2645
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    ABSTRACT: 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 143GPa and 2500K 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.
    Physics of The Earth and Planetary Interiors 02/2008; 166(3):219-225. DOI:10.1016/j.pepi.2008.01.002

Publication Stats

328 Citations
99.10 Total Impact Points

Institutions

  • 2004–2014
    • Hokkaido University
      • • Department of Natural History Sciences
      • • Faculty of Science
      • • Graduate School of Science
      • • Division of Earth and Planetary Sciences
      Sapporo, Hokkaidō, Japan
  • 1997–2010
    • Osaka University
      • Department of Earth and Space Science
      Suika, Ōsaka, Japan
  • 1999
    • Okayama University
      • Faculty of Science
      Okayama, Okayama, Japan