研究者データベース

永井 隆哉(ナガイ タカヤ)
理学研究院 地球惑星科学部門 地球惑星システム科学分野
教授

基本情報

所属

  • 理学研究院 地球惑星科学部門 地球惑星システム科学分野

職名

  • 教授

学位

  • 博士(理学)(東京大学)

ホームページURL

科研費研究者番号

  • 20243131

J-Global ID

研究キーワード

  • ペロブスカイト   中性子回折   X線回折   反応速度   固溶体   含水鉱物   高温高圧   鉱物物理化学   結晶学   鉱物学   

研究分野

  • ナノテク・材料 / 基礎物理化学
  • ナノテク・材料 / 結晶工学
  • 自然科学一般 / 固体地球科学

職歴

  • 2011年10月 - 現在 北海道大学 大学院理学研究院 教授
  • 2007年04月 - 2011年09月 北海道大学大学院理学研究院 准教授
  • 2003年11月 - 2007年03月 北海道大学大学院理学研究科 助教授
  • 1996年04月 - 2003年10月 大阪大学 大学院理学研究科 助手
  • 1994年04月 - 1996年03月 大阪大学 理学部 助手
  • 1992年02月 - 1994年03月 大阪大学教養部 助手

学歴

  • 1990年04月 - 1992年01月   東京大学   理学系研究科   鉱物学専攻 博士課程 中途退学
  • 1988年04月 - 1990年03月   東京大学   理学系研究科   鉱物学専攻 修士課程 卒
  • 1984年04月 - 1988年03月   東京大学   理学部   地学科地質鉱物 卒

所属学協会

  • Mineralogical Society of America   中性子科学会   日本鉱物科学会   日本高圧力学会   American Geophysical Union   

研究活動情報

論文

  • Ayako Shinozaki, Takaya Nagai, Hiroyuki Kagi, Satoshi Nakano
    Chemical Physics Letters 2019年11月 [査読有り][通常論文]
  • Kawano Jun, Toyofuku Takashi, Nishimura Kaede, Ueda Akiyuki, Nagai Yukiko, Kawada Sachiko, Teng Henry, Nagai Takaya
    CRYSTAL GROWTH & DESIGN 19 8 4212 - 4217 2019年08月 [査読有り][通常論文]
  • Tanaka Jun-ya, Kawano Jun, Nagai Takaya, Teng Henry
    JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES 114 2 105 - 109 2019年04月 [査読有り][通常論文]
  • Teruki Sugiura, Hiroshi Arima, Takaya Nagai, Kazumasa Sugiyama
    PHYSICS AND CHEMISTRY OF MINERALS 45 10 1003 - 1010 2018年11月 [査読有り][通常論文]
     
    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.
  • Sano-Furukawa Asami, Hattori Takanori, Komatsu Kazuki, Kagi Hiroyuki, Nagai Takaya, Molaison Jamie J, dos Santos, Antonio M, Tulk Christopher A
    SCIENTIFIC REPORTS 8 2018年10月19日 [査読有り][通常論文]
  • Hirokazu Masumoto, Jun Kameda, Hiroshi Arima, Kazumasa Sugiyama, Takaya Nagai, Yuzuru Yamamoto
    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 19 9 2991 - 3003 2018年09月 [査読有り][通常論文]
     
    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.
  • Satoko Motai, Jun Kawano, Takaya Nagai, Kohki Sowa, Tsuyoshi Watanabe
    EUROPEAN JOURNAL OF MINERALOGY 28 2 265 - 271 2016年03月 [査読有り][通常論文]
     
    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.
  • Jun Kawano, Satoshi Maeda, Takaya Nagai
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 18 4 2690 - 2698 2016年01月 [査読有り][通常論文]
     
    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.
  • Jun Kawano, Hiroshi Sakuma, Takaya Nagai
    PROGRESS IN EARTH AND PLANETARY SCIENCE 2 Apr 2:7 (WEB ONLY)  2015年04月 [査読有り][通常論文]
     
    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.
  • 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 2015年04月 [査読有り][通常論文]
     
    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.
  • Lin Li, Takaya Nagai, Yusuke Seto, Kiyoshi Fujino, Jun Kawano, Shoich Itoh
    PHYSICS AND CHEMISTRY OF MINERALS 42 2 123 - 129 2015年02月 [査読有り][通常論文]
     
    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.
  • Riko Iizuka, Kazuki Komatsu, Hiroyuki Kagi, Takaya Nagai, Asami Sano-Furukawa, Takanori Hattori, Hirotada Gotou, Takehiko Yagi
    JOURNAL OF SOLID STATE CHEMISTRY 218 95 - 102 2014年10月 [査読有り][通常論文]
     
    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.
  • Lin Li, Takaya Nagai, Tomoki Ishido, Satoko Motai, Kiyoshi Fujino, Shoichi Itoh
    PHYSICS AND CHEMISTRY OF MINERALS 41 6 431 - 437 2014年06月 [査読有り][通常論文]
     
    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.
  • 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 2014年03月 [査読有り][通常論文]
     
    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.
  • Satoko Motai, Takaya Nagai, Kohki Sowa, Tsuyoshi Watanabe, Naoya Sakamoto, Hisayoshi Yurimoto, Jun Kawano
    Journal of structural biology 180 3 389 - 93 2012年12月 [査読有り][通常論文]
     
    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.
  • 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 2012年02月 [査読有り][通常論文]
     
    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.
  • Riko Iizuka, Hiroyuki Kagi, Kazuki Komatsu, Daichi Ushijima, Satoshi Nakano, Asami Sano-Furukawa, Takaya Nagai, Takehiko Yagi
    PHYSICS AND CHEMISTRY OF MINERALS 38 10 777 - 785 2011年12月 [査読有り][通常論文]
     
    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.
  • 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 2011年03月 [査読有り][通常論文]
     
    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.
  • 永井隆哉, 浜根大輔, 藤野清志
    日本結晶学会誌 53 1 8 - 12 2011年02月 [査読有り][通常論文]
  • Naotaka Tomioka, Hitomi Kondo, Atsushi Kunikata, Takaya Nagai
    GEOPHYSICAL RESEARCH LETTERS 37 21 L21301  2010年11月 [査読有り][通常論文]
     
    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.
  • 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 2010年 [査読有り][通常論文]
  • 瀬戸雄介, 浜根大輔, 永井隆哉, 佐多永吉
    高圧力の科学と技術 20 3 269 - 276 2010年 [査読有り][通常論文]
     
    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.
  • 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 -  2010年 [査読有り][通常論文]
     
    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.
  • 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 2009年12月 [査読有り][通常論文]
     
    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.
  • 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 2009年08月 [査読有り][通常論文]
     
    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.
  • 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 2009年02月 [査読有り][通常論文]
     
    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.
  • 永井隆哉, 有馬寛, 奥地拓生, 鍵裕之, 八木健彦
    高圧力の科学と技術 19 1 15 - 23 2009年 [査読有り][通常論文]
     
    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.
  • Yusuke Seto, Daisuke Hamane, Takaya Nagai, Kiyoshi Fujino
    PHYSICS AND CHEMISTRY OF MINERALS 35 4 223 - 229 2008年05月 [査読有り][通常論文]
     
    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.
  • Kiyoshi Fujino, Keisuke Suzuki, Daisuke Hamane, Yusuke Seto, Takaya Nagai, Nagayoshi Sata
    AMERICAN MINERALOGIST 93 4 653 - 657 2008年04月 [査読有り][通常論文]
     
    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.
  • NISHIO-HAMANE Daisuke, SETO Yusuke, FUJINO Kiyoshi, NAGAI Takaya
    Phys Earth Planet Interiors 166 3-4 219 - 225 2008年02月 [査読有り][通常論文]
  • 永井隆哉, 井上徹, 八木健彦
    日本結晶学会誌 50 1 109 - 113 2008年02月 [査読有り][通常論文]
  • Hiroyuki Kagi, Daichi Ushijima, Riko Iizuka, Satoshi Nakano, Takaya Nagai
    HIGH PRESSURE RESEARCH 28 3 299 - 306 2008年 [査読有り][通常論文]
     
    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.
  • Taku Okada, Toshiharu Narita, Takaya Nagai, Takamitsu Yamanaka
    AMERICAN MINERALOGIST 93 1 39 - 47 2008年01月 [査読有り][通常論文]
     
    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.
  • Daisuke Nishio-Hamane, Yusuke Seto, Takaya Nagai, Kiyoshi Fujino
    JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES 102 5 291 - 297 2007年10月 [査読有り][通常論文]
     
    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.
  • N. Tomioka, A. Kunikata, H. Kondo, T. Nagai, T. Narita, T. Yamanaka
    METEORITICS & PLANETARY SCIENCE 42 A148 - A148 2007年08月 [査読有り][通常論文]
  • K. Komatsu, H. Kagi, T. Nagai, T. Kuribayashi, J. B. Parise, Y. Kudoh
    AMERICAN MINERALOGIST 92 8-9 1270 - 1275 2007年08月 [査読有り][通常論文]
     
    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.
  • Daisuke Nishio-Hamane, Kiyoshi Fujino, Yusuke Seto, Takaya Nagai
    GEOPHYSICAL RESEARCH LETTERS 34 12 L12307  2007年06月 [査読有り][通常論文]
     
    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.
  • Nishio-Hamane D, Seto Y, Nagai T, Fujino K
    Journal of Mineralogical and Petrological Sciences 102 10 291 - 297 2007年 [査読有り][通常論文]
  • N. Takafuji, K. Fujino, T. Nagai, Y. Seto, D. Hamane
    PHYSICS AND CHEMISTRY OF MINERALS 33 10 651 - 654 2006年12月 [査読有り][通常論文]
     
    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.
  • Y. Nakamoto, K. Ohi, T. Okada, T. Nagai, T. Yamanaka
    FERROELECTRICS 337 1361 - 1367 2006年 [査読有り][通常論文]
     
    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.
  • T Nagai, D Hamane, PS Devi, N Miyajima, T Yagi, T Yamanaka, K Fujino
    JOURNAL OF PHYSICAL CHEMISTRY B 109 39 18226 - 18229 2005年10月 [査読有り][通常論文]
     
    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.
  • T Yamanaka, Y Komatsu, M Sugahara, T Nagai
    AMERICAN MINERALOGIST 90 8-9 1301 - 1307 2005年08月 [査読有り][通常論文]
     
    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.
  • D Nishio-Hamane, T Nagai, K Fujino, Y Seto, N Takafuji
    GEOPHYSICAL RESEARCH LETTERS 32 16 L16306.1-L16306.4  2005年08月 [査読有り][通常論文]
     
    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.
  • 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 2005年 [査読有り][通常論文]
     
    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.
  • T Yamanaka, T Nagai, T Okada, T Fukuda
    ZEITSCHRIFT FUR KRISTALLOGRAPHIE 220 11 938 - 945 2005年 [査読有り][通常論文]
     
    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.
  • T Kawamoto, KN Matsukage, T Nagai, K Nishimura, T Mataki, S Ochiai, T Taniguchi
    REVIEW OF SCIENTIFIC INSTRUMENTS 75 7 2451 - 2454 2004年07月 [査読有り][通常論文]
     
    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.
  • 鍵 裕之, 永井 隆哉
    波紋 14 1 32 - 34 日本中性子科学会 2004年 [査読有り][通常論文]
  • 永井隆哉, 鍵裕之
    岩石鉱物科学 33 2 62 - 71 2004年 [査読有り][通常論文]
     
    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.
  • 永井隆哉
    高圧力の科学と技術 14 2 128 - 134 2004年 [査読有り][通常論文]
     
    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.
  • H Kagi, T Nagai, JS Loveday, C Wada, JB Parise
    AMERICAN MINERALOGIST 88 10 1446 - 1451 2003年10月 [査読有り][通常論文]
     
    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.
  • T Nagai, H Kagi, T Yamanaka
    AMERICAN MINERALOGIST 88 10 1423 - 1427 2003年10月 [査読有り][通常論文]
     
    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.
  • Takamitsu Yamanaka, Kouichi Kittaka, Takaya Nagai
    Journal of Mineralogical and Petrological Sciences 97 4 144 - 152 2002年 [査読有り][通常論文]
     
    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.
  • T Nagai, H Kagi, T Yamanaka
    SOLID STATE COMMUNICATIONS 123 9 371 - 374 2002年 [査読有り][通常論文]
     
    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.
  • 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 2001年08月 [査読有り][通常論文]
  • T Hattori, T Tsuchiya, T Nagai, T Yamanaka
    PHYSICS AND CHEMISTRY OF MINERALS 28 6 377 - 387 2001年07月 [査読有り][通常論文]
     
    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.
  • 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 2001年04月 [査読有り][通常論文]
     
    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.
  • 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 30 2 98 - 99 2001年03月 [査読有り][通常論文]
  • T Hattori, T Nagai, T Yamanaka, S Werner, H Schulz
    AMERICAN MINERALOGIST 85 10 1485 - 1491 2000年10月 [査読無し][通常論文]
     
    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.
  • T Nagai, T Ito, T Hattori, T Yamanaka
    PHYSICS AND CHEMISTRY OF MINERALS 27 7 462 - 466 2000年08月 [査読有り][通常論文]
     
    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.
  • T Nagai, T Hattori, T Yamanaka
    AMERICAN MINERALOGIST 85 5-6 760 - 764 2000年05月 [査読有り][通常論文]
     
    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.
  • Akira Yoshiasa, Genta Yagyu, Tomokazu Ito, Takamitu Yamanaka, Takaya Nagai
    Zeitschrift fur Anorganische und Allgemeine Chemie 626 1 36 - 41 2000年 [査読有り][通常論文]
     
    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.
  • Keiji Shinoda, Takaya Nagai, Nobuyuki Aikawa
    Journal of Mineralogical and Petrological Sciences 95 5 65 - 70 2000年 [査読有り][通常論文]
     
    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.
  • T Hattori, T Matsuda, T Tsuchiya, T Nagai, T Yamanaka
    PHYSICS AND CHEMISTRY OF MINERALS 26 3 212 - 216 1999年02月 [査読有り][通常論文]
     
    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.
  • A Yoshiasa, T Nagai, O Ohtaka, O Kamishima, O Shimomura
    JOURNAL OF SYNCHROTRON RADIATION 6 43 - 49 1999年01月 [査読有り][通常論文]
     
    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.
  • 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 1998年02月 [査読有り][通常論文]
     
    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.
  • O Ohtaka, T Nagai, T Yamanaka, T Yagi, O Shimomura
    PROPERTIES OF EARTH AND PLANETARY MATERIALS AT HIGH PRESSURE AND TEMPERATURE 101 429 - 433 1998年 [査読有り][通常論文]
     
    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.
  • T Nagai, O Ohtaka, A Yoshiasa, T Yamanaka, O Shimomura
    PROPERTIES OF EARTH AND PLANETARY MATERIALS AT HIGH PRESSURE AND TEMPERATURE 101 385 - 391 1998年 [査読有り][通常論文]
     
    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.
  • 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 1998年 [査読有り][通常論文]
     
    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.
  • 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 1998年 [査読有り][通常論文]
     
    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.
  • T. Nagai, S. Mori, O. Ohtaka, T. Yamanaka
    Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 7 125 - 127 1998年 [査読有り][通常論文]
     
    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.
  • T. Yamanaka, T. Nagai
    Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 7 34 - 39 1998年 [査読有り][通常論文]
     
    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.
  • T Nagai, T Hattori, T Tsuchiya, T Yamanaka
    SOLID STATE COMMUNICATIONS 107 5 223 - 225 1998年 [査読有り][通常論文]
     
    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.
  • S Kawasaki, T Aketa, F Okino, H Touhara, T Hattori, T Nagai, T Yamanaka
    SOLID STATE COMMUNICATIONS 108 10 749 - 752 1998年 [査読有り][通常論文]
     
    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.
  • T Nagai, T Yamanaka
    PHYSICS AND CHEMISTRY OF MINERALS 25 1 1 - 7 1997年11月 [査読有り][通常論文]
     
    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.
  • NAGAI Takaya, OHTAKA Osamu, YAMANAKA Takamitsu
    Mineralogical journal 19 4 147 - 154 1997年10月 [査読有り][通常論文]
  • T Yamanaka, T Nagai, T Tsuchiya
    ZEITSCHRIFT FUR KRISTALLOGRAPHIE 212 6 401 - 410 1997年 [査読有り][通常論文]
     
    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.
  • 永井隆哉
    高圧力の科学と技術 4 1 35 - 41 1995年 [査読有り][通常論文]
     
    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.
  • NAGAI T, YANO K, DEJIMA M, YAMANAKA T
    Mineral J 17 4 151 - 157 1994年10月 [査読有り][通常論文]
  • 永井隆哉
    化学と工業 46 4 677  1993年04月 [査読有り][通常論文]

書籍

  • 日本鉱物科学会 
    朝倉書店 2019年 (ISBN: 9784254162769)
  • マイクロビームアナリシス・ハンドブック
    (担当:共著範囲:第7章2節 X 線・放射光利用分析法)
    オーム社 2014年06月
  • 地球惑星科学入門
    (担当:共著)
    北海道大学出版会 2010年 (ISBN: 9784832982192)
  • 地球の変動と生物進化
    (担当:共著)
    北海道大学出版会 2008年

講演・口頭発表等

その他活動・業績

受賞

  • 2009年 日本鉱物科学会論文賞
  • 1998年 日本鉱物学会論文賞
     
    受賞者: 永井隆哉

共同研究・競争的資金等の研究課題

  • 日本学術振興会:科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2008年11月 -2014年03月 
    代表者 : 八木 健彦, 永井 隆哉, 井上 徹, 内海 渉, 服部 高典, 片山 芳則, 飯高 敏晃
     
    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。
  • 日本学術振興会:科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2008年 -2012年 
    代表者 : 永井 隆哉, 赤坂 正秀, 栗林 貴弘, 深澤 裕, 佐野 亜沙美, 内海 渉, 神山 崇
     
    鉱物物理研究において今後ますますの活用が期待される研究手法である中性子回折法を用いて、いくつかの重要な含水鉱物の水素位置に関する情報を、常圧、常圧高温、常温高圧、高温高圧と幅広い温度圧力条件で得ることに成功した。マントル鉱物中の水素位置、水素結合の圧力誘起対称化、熱膨張の特異な挙動と水素位置の無秩序化との関係、地殻に産する固溶体鉱物中の金属元素置換と水素位置の関係など、多くの新しい知見が得られた。
  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2009年 -2011年 
    代表者 : 藤野 清志, 永井 隆哉
     
    Mg-ペロブスカイト(Pv)及びポスト-Mg-ペロブスカイト(PPv)における3価鉄のスピン転移をそれぞれ200GPa及び165GPaに至る条件下でX線発光分光法およびX線回折により調べた.これにより, Pvでは高スピンの3価鉄が50-60GPa以上でAサイトからBサイトに移って低スピンになるのに対し, PPvではその全安定領域で3価鉄はBサイトを占めて低スピンであることが明らかになった.
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2006年 -2008年 
    代表者 : 永井 隆哉, 鍵 裕之, 佐多 永吉, 藤野 清志, 藤野 清志, 瀬戸 雄介
     
    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)
    研究期間 : 2006年 -2006年 
    代表者 : 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。
  • マントル鉱物の高温高圧下での電気伝導度とX線回折の同時測定技術の開発
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2003年 -2004年 
    代表者 : 永井 隆哉
     
    電気伝導度測定とX線回折実験が同時に可能であるようなダイヤモンドアンビルセルを設計、製作し、直流二端子法による電気伝導度測定(実際には電気伝導度はサンプルの大きさに大きく依存するため、基本的には電気伝導率を測定する。)のための電気回路、GPIB経由でのデータ取り込みのコンピューターシステムを構築した。 マグネタイトFe_3O_4とウルボスピネルFe_2TiO_4を端成分とする固溶体について、いくつかの組成の単結晶を合成したものを試料にして、本科学研究費補助金を使って開発した電気伝導率・X線回折同時測定装置を使うことによつて、電気伝導度の圧力依存を測定すると同時に、X線回折パターンの測定によって電気伝導率の変化と構造変化の関係について調べた。 その結果、いずれの試料についても、ある圧力になると電気伝導率は急激に圧力依存性を示さなくなり、その変化が起こった圧力値はマグネタイトでは24GPaであったが、Tiの固溶に伴って低圧側にシフトし、ウルボスピネルでは6.5GPaであった。そして、その圧力でX線回折パターンにおいて、いくつかの回折線が分裂し二重線になっており、相変態が起こっていることがわかった。回折パターンの解析と、ウルボスピネルの圧力下における単結晶構造解析から、この相変態は対称性が立方晶系からMn_3O_4構造型の正方晶系に変化した構造相転移であることがわかった。この相転移は可逆的であり、二次相転移であると考えられる。本科学研究費で開発したシステムによって、物性(電気伝導率)の変化と構造変化の因果関係が直接的に議論できるようになったことは、今後のこの分野の展開に重要な意義を持つと思われる。
  • 単結晶を用いた高圧下格子振動解析による地球物質の高圧構造転移に関する弾性論の研究
    日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2002年 -2004年 
    代表者 : 山中 高光, 大高 理, 岡田 卓, 永井 隆哉, 吉朝 朗
     
    マントル状態での地球深部物質の高圧格子振動解析は単結晶X線回折実験と相補的な関係にある.後者からは原子間距離,結合電子,電子状態,有効電荷の情報が得られるが,格子間力のエネルギ情報は格子振動解析から与えられる.高温,高圧下でのレーザーラマン分光装置を用いて温度や圧力を関数にした結晶力学について議論することを本研究の目的とした. (1)本科学研究費は14〜16年度3年間継続で,始めに格子振動解析の主要装置である日本分光社製の顕微ラマン装置についてラマン散乱スペクトルシステムの立ち上げとその性能テストを行い,低波数領域から目的のバンド領域で,解析に必要な分解能の達成を確認した. (2)国内,国外で粉末試料の高圧ラマン分光実験は行われてきたが,格子振動解析を目的に,異方性を考慮した単結晶試料の高圧下でのラマン分光実験はまだ報告はない.結晶試料方位を規定して高温高圧ラマン散乱実験装置を開発した. (3)マントル中でMgSiO_3は輝石→ガーネット→イルメナイト→ペロブスカイトに転移するが,MgSiO_3,MgGeO_3,MgTiO_3のイルメナイトを合成しこれら3試料の加熱ラマン散乱実験から原子の熱振動による格子間力の違いを議論した. (4)上記3試料について高圧ラマンスペクトル解析を行った.DACに試料と圧力媒体を装填し,圧力を変数にしてラマンシフトを測定し,格子間力の圧力効果を議論した. (5)マントル中の水について理解するために,ケイ酸塩鉱物の温度圧力変化に伴うラマンスペクトルの逐次測定を行う.O-H…0の水素結合の圧力効果の究明し,圧力転移についてその起因力となる体積圧縮率,弾性率,状態方程式等に関して意義付けを行なった. (6)放射光を利用した単結晶構造研究を行い,固体電子論の立場から議論してきた,電子密度の圧力変化,格子歪み,電荷移動等の研究と,高温・高圧状態での単結晶ラマン散乱実験によって地球内部物質の格子力学的観点から議論をした.
  • Rietveld法を用いた高温高圧下でのマントル鉱物の結晶構造精密化
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2001年 -2002年 
    代表者 : 永井 隆哉
     
    高圧下での粉末X線回折図形の質の向上、高温高圧相の合成のための、レーザーアニーリング法とレーザー加熱を可能にするNd:YAGレーザーを導入した。レーザーアニーリングの効果は大で、非静水圧によりブロードな回折線が、歪の解消により鋭くなり、Rietveld解析に耐えうる回折線を得ることができるようになる。アニーリング条件の最適化を興味の対象とする鉱物に対して行い、レーザーアニーリング法を活用しながら、主に放射光施設で高圧下での回折実験を行った。 高圧下で得られた粉末X線回折データの解析から、いくつかの物質についての圧縮挙動を原子レベルで記述した。KHCO_3、NaHCO_3、ゲータイトといった含水鉱物の圧縮挙動は、水素結合が存在する酸素-酸素間の短縮が主な圧縮機構で、水素結合の対称化に絡んで興味深い水素結合の強度と圧縮挙動の関係を得た。Al_2O_3,NiTiO_3に関しては、レーザーアニーリングを行いながら回折線を収集し、圧媒体固化後の圧力下でも信頼性のあるRietveld解析が可能なデータを得ることに成功した。レーザー加熱実験から、MgCO_3と鉄は40GPa,2000℃と40GPa,1000℃のいずれの条件でも、反応を示唆する結果は得られず、少なくとも下部マントル上部まではこの反応は起こらない。またCaSiO_3ペロフスカイトを試料とした実験では、圧力20GPa、温度1500-1600Kでの回折パターンを得た。DAC内の試料構成にはまだ改善の余地があるが、CaSiO_3ペロフスカイトの回折線そのものは比較的スムースであり、超高温高圧下でのRietveld解析に耐えうる質の回折線が収集できる可能性が示唆される。外熱式DACに油圧制御機構を組み込み、CaOの精度の高い状態方程式を得、CaSiO_3ペロフスカイトが下部マントル最下部の温度圧力条件で分解する可能性を議論した。
  • 地球内部物質の高圧高温下での結晶構造と物性に関する研究
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 1999年 -2000年 
    代表者 : 山中 高光, 永井 隆哉, 大高 理, 吉朝 朗, 下村 理, 八木 健彦
     
    珪酸塩鉱物の応力下での構造安定性,また相平衡の研究が多くなされてきた.一方結晶内の転位密度、格子変形の研究から,圧力誘起相転移や固相-固相転移と準安定相の存在や,その機構を究明することも地殼内の固体流動を議論する上で重要である.また地球を構成する岩石・鉱物などの多結晶体の応力場での構造や組織の変化を理解するために,地球内部で起こっている物理化学的また力学的過程(温度,圧力,分圧,電場,磁場,化学ポテンシャルなどの変化)を再現し定量的な実験を基に動的解析を行った.パリ第7大学(Inst.Physque du Globe)のグループはダイヤモンドアンビルを用いて高圧下で熱伝導の測定システムの開発し,世界的に優れた研究を行ってきた.本研究ではパリ大学と共同研究として以下の実験を行ってきた. (1)地殼物質であるオリビン(Mg1-x,Fex)2SiO4について高温高圧状態で電気伝導度の測定した,その結果を基に地球内部の温度(geotherm)を推定する.マルチアンビル高圧装置を用いて最高7GPaで1000℃までの条件で,上記試料の測定を行った. (2)Fe2SiO4について6GPaでオリビン構造のがらスピネル構造への高圧転移の電気伝導度が著しく変化することが明らかになった.電気伝導機構はFe^<2+>⇔Fe^<3+>電子ホッピング機構であることが分かった. (3)下部マントル物質であるウスタイト(Mg1-xFex)Oの電気伝導のFeの組成変動(x=0.1,0.3,0.5)とともに圧力(最高30GPa),温度を変数として測定をダイヤモンドアンビルを用いて行った.Feの増加と供に電気伝導が増加するのはd電子の配位結合の軌道に基づくことが判明した. (4)分担者のパリ大学のProf.J.P.Poirier(Inst.Physque du Globe)のグループと共に共同実験テーマとして,地球中心核物質のFeの高圧高温での融体の相平衡実験を,SPring-8においてマルチアンビル装置による高圧回折装置を利用してを用いて行った.本研究を行うためパリ大学のDr.D.Andraultを招聘し,また大高,下村等が実験協力者として行った.
  • マントル物質の高圧・応力場での非平衡過程の格子不安定性とカイネティックス
    日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 1998年 -2000年 
    代表者 : 山中 高光, 永井 隆哉, 大高 理, 吉朝 朗
     
    スラブの沈み込みや,固体流動,マントルの物質移動など現象を理解するために,物質を取り巻く環境の変化に即応して地球内部物質が圧力や熱誘起により,構造相転移,分解,離溶,融解,結晶化など色々な構造変化の素過程,過渡現象や前駆現象X回折逐次測定を行うことを本研究の目的としている.地球内部の環境を加熱装置を内蔵したダイヤモンドアンビル加圧装置を用いて再現し,結晶構造変化の運動論を,応力と温度を関数にして,時間分割実験システムを開発した.そのシステムを用いて高圧力,応力場で主にケイ酸塩スピネル,ガーネット,ペロブスカイトなどの上部・下部マントル物質の高圧・応力場での非平衡過程の格子不安定性とカイネティクスの研究を開始した. X線検出装置として精度の高いX線角度分散スペクトルが短時間で得られるImaging Plate(IP)検出器をX線回折装置に設置し高温高圧状態での回折実験装置を確立した.購入した理学電機製のRAXIS-IVの性能テスト(位置分解能,検出効率,ダイナミックレンジ,再現性等)を行ない当初目的の仕様を確認した.電気的に検出光子数が瞬時に記憶回路に転送システム,また回折強度データ整理と表示のソフト開発を行なってきた.研究室に既に存在する回転対陰極強力X線発生装置に設置したHUBER社製の四軸自動回折計にIP検出器を取り付け一体型の装置にした.微視的にはエネルギー・時間・空間の秩序度とそれらのゆらぎであり,その際準安定状態として,熱力学で定義される相が存在する場合と,準安定相が存在する場合がある.時間的には時間分割,時間変動で観察や測定ができる.高圧状態で,単結晶X線回折実験が可能になり,上記した色々な構造変化の逐次測定をし,それらの有機的な関係を調べ地球内部物質の変態の運動論を議論する.実験結果から固体流動の機構や遷移帯での地震波速度の異常について,物質科学的な知見が得られると思う.
  • Charge Coupled Davice(CCD)を用いた高圧下時間分割X線回折実験システムの開発
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 1998年 -2000年 
    代表者 : 山中 高光, 永井 隆哉, 吉朝 朗, 常深 博
     
    本研究の目的は地球内部の温度圧力条件を再現し,地殻、マントル、さらに中心核を構成する物質の構造の究明することである.そのために今年度は,高圧・高温下での物質の変化過程を秒単位で時間分割単結晶X線回折方法によって測定・観察するシステムを検討してきた.構造の変化の運動論や,その転移や分解反応の機構を解明するためには、高温・高圧システムと二次元X線強度測定検出装置を用いて測定を迅速に行う時間分割測定が可能なCharge Coupled Devise(CCD)検出器を購入することにした.近年開発されたCCDを色々な観点から検討し結果,理学電機社の技術人と設計し,開発をすることにした.購入した理学電機製のCCD検出器の性能テスト(位置分解能,検出効率,ダイナミックレンジ,再現性等),また回折強度データ整理と表示のソフト開発を行なってきた.研究室に既に存在する回転対陰極強力X線発生装置に設置したHUBER社製の四軸自動回折計にCCD検出器を取り付け一体型の装置にした.時間軸を考慮した加圧状態出の結晶の構造変化の動的過程を遂時測定するため,外熱型の電気抵抗加熱装置を内蔵したダイヤモンドアンビル加圧装置を改良し,最高温度550℃,30GPaまで加圧できるシステムの開発は既に終了した.将来このシステムは高圧下での結晶変態のカイネティックスの研究のみならず、物性測定や地球科学現象等の研究に多大な貢献をすると思われる.さらにSPring-8やPFでの利用は新分野の開拓にもなろう. (1)構造相転移の逐次解析(非晶質過程、マルテンサイト転移、融解等)、 (2)分解反応(離溶、脱水、脱ガス、放射線損傷等を含む)、 (3)結晶成長過程(気相成長、融液成長を含む)、 (4)固体反応、 (5)電子遷移状態解析等の現象を扱う物性物理、金属、材料科学、無機科学、電子工学などの諸科学に非常に強力な実験手段になる
  • 圧力誘起相転移のカイネティクスに影響を及ぼす要因の定量的評価
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 1998年 -1999年 
    代表者 : 永井 隆哉
     
    (1)粉末と単結晶を使った高圧回収実験から、石英-コーサイト転移のカイネティクスに結晶粒径効果がある可能性が示唆され、粒径が大きいほど転移の活性化エネルギーが低くなる傾向を得た。また、静水圧下では核生成は粒表面のみでしか起こらないのに対し、差応力下では粒内部での核生成が観察され、静水圧性が核生成に影響を及ぼすことが認められた。またこの相転移が核生成・成長のメカニズムで起こっていることが回収実験、その場観察実験両方から明らかになった。しかし核生成は相転移の極初期に完了しており、核生成が成長を律速する過程を観測することは困難であった。そこでSPring8の強力な放射光を使って1ステップ15秒程度の短時間での時分割X線回折実験を高圧高温下で行い、その結果、初めて核生成の律速していると予想される相転移の極初期の様子をとらえることに成功した。1 (2)放射光とを使った高圧粉末X線回折実験の結果にRietveld法を適用して、格子定数の圧力変化からのみではなく原子レベルでの圧縮挙動を調べることによりCa(OH)_2とMg(OH)_2の圧縮挙動の類似点と相違点を明らかにした。圧縮初期では両者とも八面体層間が著しく圧縮されるが、層間の酸素-酸素間距離が2.75Åに達する約10GPaでCa(OH)_2は非晶質化を起こし、Mg(OH)_2は圧縮メカニズムが酸素パッキングに支配されるメカニズムに変化し、著しく異方的な圧縮挙動が等方的に近くなることが明らかになった。この挙動の違いはMgとCaの電気陰性度の違いが形成される水素結合の強度に影響していることが原因である可能性が示唆された。
  • 地球内部物質の高圧高温下での結晶構造と物性に関する研究
    日本学術振興会:科学研究費助成事業 国際学術研究
    研究期間 : 1996年 -1997年 
    代表者 : 山中 高光, 永井 隆哉, 大高 理, 吉朝 朗, 八木 健彦, 下村 理, KUHS Werner, SCHULZ Heinz
     
    地殻・マントルにおける流動現象や地震の発生機構、沈み込むスラブの運動といったダイナミクスを理解するために、構成する物質・鉱物の高温・高圧状態での塑性変形や相転移などの物質科学的な研究を行う。ミュンヘン大学を中心とした中性子、放射光を利用する結晶学、鉱物学者等と、我々の高圧発生技術と相互協力をし固体地球科学について共同で推進してきた。 岩石・鉱物などの多結晶体の応力場での構造や組識の変化から物質流動が起こす。これらを理解するためには、地球内部で起こっている物理化学的また力学的過程(温度、圧力、分圧、電場、磁場、化学ポテンシャルなどの変化)を再現し定量的な実験を基に動的解析をする必要がある。以下の3研究課題について共同研究を行う。この研究は単に高圧・高温下での物質構造・組識研究の知見を得るばかりでなく、地殻流動、深発地震、マグマの流動などの機構解明にも一助となる。また日独の鉱物科学分野での多くの波及効果が期待される。 1.地球深部物質の上昇、下降に伴う構造変化。(物質の温度-圧力-時間経路による固体内拡散の精密測定と計算機シュミレーションによる解明) 2.高温高圧下での応力場における結晶構造変化や弾性変形、塑性変形を実験的に解明 3.スラブの移動の起因力となる物質の熱膨張率、体積圧縮率、弾性波速度、粘性などの物性の温度・圧力関数とした物質流動機構の解明)
  • 高圧応力過程での相変態の動的観察とそのカイネティクス
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 1996年 -1997年 
    代表者 : 山中 高光, 永井 隆哉, 大高 理, 植田 千秋, 吉朝 朗
     
    本実験では地殻・マントルを形成するケイ酸塩鉱物、水和鉱物のや運動論を議論する。温度や圧力が変動した場合、熱力学的に安定な構造に必ずしも相転移したり、分解するとは限らない。充分な活性化エネルギーが無い場合はOstwal d Step Ruleにより準安定相や不安定中間相に留まることが明かになった。 (1)蛇紋岩のような塩基性水和鉱物の類似物としてCa(OH_2)の単結晶を用いてダイヤモンドアンビル(DAC)加圧装置を用いて常温で静水圧下で相転移過程のX線回折実験を行なった。その結果格子の揺らぎにより高圧安定相CaCl_2に転移する以前に非晶質状態になる。この状態変化は可逆的であった。 (2)DACに内熱式の白金ヒーターを設置して、応力場の地温勾配に対応させた実験を行う事により一層実際の環境を再現した圧力誘起による構造変化を解明も行なった。石英(SiO_2)はコ-サイトに高圧転移について、高温・高圧下で結晶構造変化について時間分割測定を行い、逐次観察と動的構造の研究を行った。圧力誘起構造変化の観測と、熱膨張率、体積圧縮率、弾性率、状態方程式、物性変化の研究を行った。静水圧性の異なる加圧と加熱過程の違いから、相転移温度や圧力誘起構造変化の運動論を議論した。 (3)高圧下で結晶構造の格子が弾性変形や塑性変形により、密度の高い非晶質相の存在理由を回折実験と、局所構造解析を行なうEXAFSやラマン散乱実験から明らかにした。FeGeO_3やまたSrO_2の高圧相であるGeO_2の結晶、ガラス、非晶質相の密度変化がそれぞれ異なることも確認した。 (4)二体間ポテンシャルに基づく分子動力学理論(MD)を用い、種々の応力過程での構造変態のシュミレーションをGeO_2について変態機構や弾性定数を求めた。
  • 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)
    研究期間 : 1996年 -1996年 
    代表者 : 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。
  • 鉱物の蒸発と凝縮のカイネティクス-反応速度の精密測定
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 1995年 -1996年 
    代表者 : 土山 明, 永井 隆哉, 山中 高光, 植田 千秋
     
    原始惑星系円盤における惑星形成とこれにともなう惑星物質の分化には、蒸発・凝縮過程が重要な役割を果したと考えられる。これに関して、本研究では次のような成果を得た。 1.超高温天秤を用いて試料重量の時間変化より蒸発・凝縮量の時間依存性を精密に求め、そのカイネティクスを厳密に議論するための実験技術開発をおこなった。いくつかの含水珪酸塩鉱物の脱水実験(水の部分的な非調和蒸発実験)を一定温度でおこない、脱水量の時間変化からそのカイネティクスが議論できることを確認した。さらに、アルカリ珪酸塩メルトからのアルカリ元素(NaおよびK)の蒸発実験を、1気圧Ar雰囲気中から真空までの低圧雰囲気下でおこない、アルカリ元素の蒸発速度を求めた。 2.珪酸塩メルトからのNaの蒸発とコンドリュールの成因について、新しいモデルを提唱し、従来考えられていたような開放系でのフラッシュ加熱だけでなく、閉鎖系での比較的ゆるやかな加熱でもコンドリュール生成が可能であることを示した。これによりコンドリュール成因論に新しい観点を与えた。 3.Fe/S系鉱物(金属鉄とトロイライト)の蒸発とFe/S分別について蒸発実験をおこない、その蒸発のカイネティクス(蒸発様式と速度)を明らかにした。これらの結果をもとに、原始太陽系星雲での金属鉄およびトロイライト粒子の蒸発速度の推定をおこない、原始惑星系円盤形成モデルと組み合わせることにより、原始太陽系星雲におけるFe/S分別を議論した。
  • 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
    日本学術振興会:科学研究費助成事業 奨励研究(A)
    研究期間 : 1995年 -1995年 
    代表者 : 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。
  • 惑星物質の蒸発実験-分解蒸発の役割
    日本学術振興会:科学研究費助成事業 一般研究(C)
    研究期間 : 1993年 -1994年 
    代表者 : 土山 明, 永井 隆哉, 田窪 宏, 山中 高光, 松田 准一, 植田 千秋
     
    地球型をつくる重要な鉱物(フォルステライト、金属鉄、トロイライト)の蒸発実験をおこない、蒸発速度とその蒸発係数を求めた。フォルステライトは水素雰囲気中で調和蒸発し、直線則に従う。その蒸発係数の温度依存性は、水素雰囲気中での蒸発も自由蒸発と類似した蒸発機構でおこることを示した。これにより原始太陽系星雲でのフォルステライトの蒸発速度を求めることができるようになった。金属鉄の蒸発も直線則に従い、蒸発係数は1に近いことがわかった。一方、トロイライトは金属鉄を残渣とする分解蒸発をするが、トロイライト-金属鉄界面反応律速のため直線則に従う。これらの結果などをもとにして、地球型をつくる重要な鉱物について、原始太陽系星雲中での蒸発を含む様々な条件での蒸発速度をコンパイルした。これを用いて、原始太陽系星雲における鉱物の蒸発にともなう元素分別(Mg/SiおよびFe/S)を議論した。これによるとエンスタタイトの分解蒸発はおこらず、カイネティックな理由によりみかけ上の調和蒸発がおこることが予想され、Mg/Si分別はおこらなくなる。しかしながら、ダストが非晶質Mg珪酸塩である場合には、ダスト中での元素の拡散係数が結晶中に比べると大きいので、Mg/Si分別がおこる可能性がある。一方、トロイライトは原始太陽系星雲中でも分解蒸発することが予想され、Fe/S分別がおこると考えられる。さらに鉱物の蒸発速度を用いて、固体からの蒸発にともなう同位体質量分別についてモデル化をおこなった。同位体質量分別がおこるかどうかは、蒸発速度、固体内の拡散係数、および固体のサイズによって、またその絶対量は蒸発分子質量に依存する同位体分別係数によって決まる。これを用いて、フォルステライト、金属鉄の蒸発にともなう同位体分別を議論し、隕石中にみられる同位体分別を示す物質について分別の条件を推定した。
  • 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)
    研究期間 : 1993年 -1993年 
    代表者 : 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。

教育活動情報

主要な担当授業

  • 地球惑星物質学概論
    開講年度 : 2019年
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 地球惑星物質、鉱物、結晶化学、結晶構造解析、固溶体、相変化、熱力学、相図
  • 地球惑星物質学特論
    開講年度 : 2019年
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 地球惑星物質、鉱物、結晶化学、結晶構造解析、固溶体、相変化、熱力学、相図
  • 地球惑星科学実験Ⅲ
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 限界レイノルズ数,水の波動特性,土壌水の移動,同位体,環境化学,分析化学,電子顕微鏡,隕石,結晶成長,地質温度・圧力計,海洋プレートの沈み込み,付加体,褶曲・断層の形成,マグマ,相転移,結晶学,X線回折,鉱物合成
  • 地球惑星科学実験Ⅰ
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 地球惑星固体物質、偏光顕微鏡、岩石学、鉱物学、火成岩、堆積岩、変成岩、隕石、流体包有物
  • 地球惑星科学Ⅰ
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 固体地球,地球の構造と構成物質,地球史,変動する地球,自然災害
  • 鉱物学
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 鉱物、結晶構造、化学組成、物理的性質、安定性、相図
  • 鉱物物理化学
    開講年度 : 2019年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 鉱物、物性、熱力学、結晶学、拡散、分配、反応、相律、相図、結晶成長

大学運営

学内役職歴

  • 2019年4月1日 - 2021年3月31日 大学院理学研究院副研究院長

委員歴

  • 2018年09月 - 2020年09月   日本鉱物科学会   理事
  • 2016年09月 - 2018年09月   日本鉱物科学会   理事
  • 2014年09月 - 2016年08月   日本鉱物科学会   庶務幹事
  • 2012年09月 - 2014年09月   日本鉱物科学会   庶務幹事
  • 2004年09月 - 2007年09月   日本鉱物科学会   評議員   日本鉱物科学会
  • 2004年09月 - 2006年09月   日本鉱物科学会   庶務幹事   日本鉱物科学会
  • 2002年 - 2005年   日本高圧力学会   評議員   日本高圧力学会


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