Research Themes

• CaSiO3デイブマオアイトへのAlの固溶についてアナログ物質SrTiO3からのアプローチ
  科学研究費助成事業
  01 Apr. 2024 - 31 Mar. 2027
  永井 隆哉
  日本学術振興会, 基盤研究(C), 北海道大学, 24K07181
• Coordination and research support of the project "Earth Science Based on High-Pressure and High-Temperature Neutron Experiments
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
  13 Nov. 2008 - 31 Mar. 2014
  YAGI Takehiko, UTSUMI Wataru
  本研究は平成20年度から24年度まで5年間にわたり行われた新学術領域研究「高温高圧中性子実験で拓く地球の物質科学」の総括と支援を行うために実施されたものである。新学術領域研究では東海村のJ-PARCに高圧中性子実験に特化した新しいビームライン、”PLANET”を建設し、それを用いて地球深部物質に対する高圧下の中性子回折実験を行い、特に水が及ぼす影響に着目して地球深部構造の研究を展開することを目的とした。そこで、予定通り建設されたPLANETを使ってさまざまな成果が出始めたことを踏まえ、それらを総括してさらなる発展の方向性を議論することや、新しい装置にが今後広い学問分野での研究に使われるようさまざまな広報活動を行うことが、本研究の目的となった。その方針に従い、さまざまな研究会を開催したり、国際会議で報告するために人を派遣したり、報告書やパンフレット等を作成した。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), 20103001
• Incorporation mechanism of hydrogen into some minerals and its dynamical behavior at high pressure
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
  2008 - 2012
  NAGAI Takaya, AKASAKA Masahide, KURIBAYASHI Takahiro, NFUKAZAWA Hiroshi, SANO Asami, UTSUMI Wataru
  More and more application of neutron diffraction technique is expected in the field of mineral physics in the near future. Crystallographic information about hydrogen positions in some important hydrous minerals was successfully obtained in quite wide range of pressure-temperature conditions. These could give some new insights of hydrogen positions in some mantle minerals, a pressure-induced hydrogen-bond symmetrization mechanism, the relationship between specific thermal expansion and dynamical behavior of hydrogen atoms, and the relationship between cationic substitution and hydrogen positions in some crustal minerals.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Hokkaido University, Competitive research funding, 20103002
• Spin transition of ferric iron in the lower mantle
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
  2009 - 2011
  FUJINO Kiyoshi, NAGAI Takaya
  Spin transitions of ferric iron in Mg-perovskite(Pv) and post-Mg-perovskite(PPv) were examined up to 200 GPa and 165 GPa, respectively, by X-ray emission spectroscopy and X-ray diffraction. The results showed that high spin ferric iron in Pv moves from the A-site to the B-site above 50-60 GPa and becomes low spin, while ferric iron in PPv occupies the B-site and is low spin in its whole stability region.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), 21540491
• Origin of diamonds derived from the Earth's lower mantle
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
  2006 - 2008
  NAGAI Takaya, KAGI Hiroyuki, SATA Nagayoshi, FUJINO Kiyoshi
  人類を魅了してやまないダイヤモンド。その中で近年多く認識されるようになった地下670km以深の下部マントルと呼ばれる領域を起源とするダイヤモンドは、炭酸塩鉱物が石英と一緒に地球深部の下部マントル中心部にまで沈み込んだときに生成された可能性があることを実験的に初めて明らかにした。このことは炭酸塩鉱物という地球表層に存在する鉱物が、地球深部に取り込まれる地質学的プロセスが存在し、さらに、生成したダイヤモンドが再び地球上にもたらされるというダイナミックな炭素循環が地球に存在することを意味する。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 18340167
• 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
  科学研究費助成事業 基盤研究(C)
  2006 - 2006
  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。
  日本学術振興会, 基盤研究(C), 東京大学, 18634010
• Development of simultaneous measurements system of electric conductivity and x-ray diffraction on mantle minerals at high pressure and temperature
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
  2003 - 2004
  NAGAI Takaya
  A diamond anvil cell, which can apply to electric resistance and x-ray diffraction measurements simultaneously, was designed in this research project. The DAC is basically modified the lever & spring type DAC and two electrodes model for electric resistance measurements is installed the DAC.
  A series of single crystals of the magnetite (Fe_3O_4)-ulvospinel (Fe_2TiO_4) solid solution were synthesized by the FZ method. Then, electric resistance measurements were performed on those samples and x-ray diffraction measurements were also performed at the same time.
  Electric resistances on all samples decrease gradually with increasing pressure probably due to the electron hopping and the band overlapping mechanism. However, the electric resistances suddenly show no pressure-dependency-above some critical pressures. The critical pressure increases with iron content in the solid solution of Fe_<3-x>Ti_xO_4. For example, the critical pressures are about 6.5GPa for Fe_2TiO_4 and about 24GPa for Fe_3O_4. X-ray powder diffraction patterns obtained above the critical pressure showed that some single diffraction peaks split into doublet peaks above the critical pressure. The evidence suggests a structural transition occurs at the critical pressure. According to the single crystal structure analysis experiments on Fe_2TiO_4 at high pressure, the structural transition could be assigned as the transition from cubic to tetragonal symmetry and the Mn_3O_4 type structure can be proposed as a candidate of the high-pressure form of Fe_2TiO_4. The newly designed system in this research project can provide some interesting and important information about the relationship between the crystal structures and electric resistances.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 15340187
• Lattice dynamics study of pressure-induced structure change of earth materials under high pressure using single crystals.
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
  2002 - 2004
  YAMANAKA Takamitsu, OHTAKA Osamu, OKADA Taku
  For the investigation of earth interiors under high-temperature and high-pressure condition of the mantle, lattice dynamical studies under high pressures are complementary with X-ray diffraction structure analyses using single crystals. By means of the latter experiments, the crystal structure information can be provided from the interatomic distances, bonding electron, effective charge and electronic state. In formation of interatomic force can be provided from lattice dynamical analysis. The present experiment aims to elucidate crystal dynamical charge as functions of temperature and pressure by means of laser Raman spectroscopy.
  (1)At the first stage of this experiment during these three years(2002-2004) with the aid of the Scientific Research (A)(2)development and test of the microscopic Raman spectrometer have been made under extreme conditions.
  (2)The new lattice dynamical experimental system has been performed for the purpose that Raman spectral studies taking into account the crystallographic anisotropy have been executed using single crystal.
  (3)In order to comprehend the phase transformation of MgSiO3 polymorphs in mantle, pyroxene-garnet-ilmenite-perovskite, three synthetic ilmenites, MgSiO3 MgGeO3and MgTiO3, are applied for the measuring Raman shift with compositional effect.
  (4)Pressure effect of these three ilmenites has been clarified as a function of pressure using diamond anvil pressure cell (DAC), in which powder sample and transmitting media are installed.
  (5)For the purpose of understanding the water presence in the mantle, kinetic studies of Raman spectra of hydrous silicate minerals have been conducted. From the investigation of pressure effect of hydrogen bond O-H…O, bulk modulus, elastic properties and equation of state have been discussed for pressure-induced transformation.
  (6)Pressure effect of the electron density distribution, lattice distortion and charge transfer were investigated using synchrotron radiation from the viewpoint of solid-state electron. Phase stability of earth's interiors has been discussed from the Raman spectroscopic analyses together with the above-mentioned X-ray diffraction studies.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Osaka University, 14204053
• Crystal structure refinement of mantle minerals under high pressure and temperature using Rietveld method
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
  2001 - 2002
  NAGAI Takaya
  In-situ X-ray diffraction measurements under pressure were performed on several minerals and obtained powder diffraction patterns were analyzed by means of Rietveld structure refinement method. High pressure is generated by a diamond anvil cell (DAC) and X-ray diffraction experiments were mainly performed in synchrotron radiation facilities, such as PF and SPring8.
  Shortening of hydrogen bonded oxygen-oxygen distances controls compression of some hydrous minerals, such as KHCO_3 and NaHCO_3. A phase transition occurs on KHCO_3 at about 2.8 Gpa. It is interesting thai hydrogen bonded O-O distance in NaHCO_3 reaches to 2.4 A^^○ at 9 Gpa and this suggests a possibility of hydrogen bond symmetrization. Shortening of hydrogen bonded O-O distance also controls compression behavior of goethite and its shortening behavior is quite similar to that of ice VII.
  Laser annealing is quile useful for relaxing strain in materials caused by nonhydrostatic pressure Laser annealing was applied to compression experiments of NiTiO_3-ilmenite in PF. Obtained diffraction patterns after annealing treatment were greatly improved and Rietveld analysis could be done successfully up to 20 Gpa.
  Laser heating is a powerful method for creating lower mantle conditions on the earth. We performed insitu X-ray diffraction experiments under high pressure and temperature conditions at SPnng8 to clarify a possibility of a reaction between maguesite and iron. No evidence of the reaction was observed at 2000℃ and 1000℃ at 40 Gpa Diffraction patterns of CaSiO_3 perovskite could be observed at 20 Gpa and 1500-1600 K. Technical improvements are still needed but quite good quality diffraction patterns were recorded.
  EOS of CaO was determined by X-ray diffraction measurements using a hydraulically operated DAC and discusses a possibility of dissociation reaction of CaSiO_3 perovskile at the lowest part of the lower mantle.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Osaka University, 13440162
• Crystal structure and solid state physics of earth's interiors under high pressure and high temperature
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B).
  1999 - 2000
  YAMANAKA Takamitsu, NAGAI Takaya, OHTAKA Osamu, YOSHIASA Akira, SHIMOMURA Osamu, YAGI Takehiko
  In order to understand dynamics of mantle or earth's shell, such as subduction of slab, mechanism of deep earthquake and mantle convection, in situ investigations of material sciences of constituent substances under high pressure and temperature are significant subject. Present experimental proposal is the collaboration works between French and Japanese geophysicists with mutual relations. By making use of the facilities in ESRF in Francc and SPring-8 and Photon Factory, phase transitions of oxides and silicates was studied under compression or stress field. Studies of solid state physics of electric conductivity, conductivity, elastic coefficient and thermal expansion coefficient were made using diamond anvil or multianvil high-pressure apparatus. The following experiments were executed :
  Electric conductivity measurement of olivine (Mg1-x, Fex)2SiO4 under high pressure and high temperature was carried out by using multianvil high-pressure apparatus. Thc measurement was conducted at temperature up to 1000 and pressure up to 6GPa. Geothermal change with depth can be estimated from the experimental results
  The electric conductivity measurement of Fe2SiO4 indicate a large gap of the conductivity at the olivine-spinel transition at about 6GPa. It is clarified that the carrier of the conduction is attributed to the Fe^<2+>⇔Fe^<3+> electron hopping rather than hole.
  ÅiCRÅjBy using diamond anvil high-pressure cell, electric conductivity of wustite (Mg1-x, Fex)O, one of major lower mantle substance, was measured measurement as functions of pressure and temperature together with Fe composition (x=0.1, 0.3, 0.5). This experiment was carried out at Inst. Physque du Globe, ) Paris University. Activation energy of electric conductivity was elucidated. With increasing Fe content in the solid solution the conductivity is elevated. The d-electron configuration of Fe ion in the bonding electron raises the conductivity.
  ÅiCSÅjCollaboration work with Prof.J.P.Poirier (Inst.Physque du Globe) is the investigation of the melting curve of iron metal, earth core material at extremely high temperature over 2000℃ under high pressure.The experiment was made with the multianvil apparatus and synchrotron radiation at SPring-8. For this experiment The present Grant-in-Aid supported the travel fee of Dr.Andrault. Dr.Ohtaka of Osaka University and Dr.Shimomura of SPring-8 stuff were supporting members.
  All experimental results have been reported at several International Conference or workshop and they were published in the science journals.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B)., Osaka University, 11694076
• Lattice instability and kinetic study of mantle substances in the nonequilibrium process under high-pressure and high stress field
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A).
  1998 - 2000
  YAMANAKA Takamitsu, NAGAI Takaya, OHTAKA Osamu, YOSHIASA Akira
  Structure changes of EarthAfs interiors under compression, such as phase transformation, decomposition, amorphization or solid reactions have been discussed by the lattice instability due to the plastic and elastic deformation. Their athermal structure changes become more crucial problems in order to elucidate geophysical dynamical process. In situ pressure-induced structure changes have been investigated by synchrotron radiation. Anisotropic structures such as chain structure or layered structures like pyroxene and olivine are subjected to a large effect of the shear stress in the mantle. Nonhydrostatic condition gave an anisotropic lattice deformation, which is different from those hydrostatic compression. The following experimental results have been published in science jourals and reported at international conference or domestic science anual meetings :
  (1) At kinetically low temperatures atomic mobility is not large enough to generate thermodynamically stable phases. The phase transition is possible by the non-diffusion martensic transformation or small atomic displacement under stress field. FeGeO3 clinopyroxene showed a reversible transformation to high-pressure phase (pseudo ilmenite) under hydrostatic condition, which was newly found. Then it transforms to ilmenite and further perovskite structure. This transition path was firstly found.
  (2) The structure changes are resulted from the elastic transformation mainly due to the virial theorem between external pressure and interatomic forces. Electron density measurement of SiO2 stishovite under high pressures up to 50GPa was clarified by using the newly devised diamond anvil and synchrotron radiation. Through single-crystal structure analysis the bonding electron density changes with pressure was confirmed.
  (3) Kinetic study of quartz-coesite transition was carried out by time-resolved diffraction experiment using multianvil high-pressure apparatus at SPring-8. Nucleation and growth were separately analyzed resulting in giving the transition rate and activation energy. It is clarified that the nucleation starts at the crystal surface or grain boundary.
  (4) Pressure-induced amorfization of hydrates were examined and two different types of the elastic and plastic deformation of lattice transition bring the amorfization.
  (5) MD calculation suggested that those phase transformations and their dynamical processes reflect the mechanism of elastic instability, which is a precursor atomic movement on the transition process. Some sublattices such as dense zone are preserved and the others are deformed in the random fashion. Elastic constants cij as a function of pressure calculated from MD reveal elastic instability in the course of structure transformation. The lattice instability can be interpreted by elastic tensors based on BomÅfs criterion. Under the condition that some elastic tensors or their combination become negative, structure becomes unstable resulting in the transformation.
  (6) Structure anisotropy brings the variation of metastable phases in the kinetics of phase transformation under pressure by OstwaldÅfs step rule. Then thermodynamically stable phases are not only candidates found in nature. Nonhydrostatic or quasihydrostatic condition brings metastable or intermediate phases in the proen of phase transition.
  (7) High-pressure EXAFS spectroscopy brought the local structure of solid ionics. Anharonic thermal effect on the pair potential of gold metal was observed by high-tcmperature and pressure study.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A)., Osaka University, 10304044
• Development of time resolved diffraction study under high pressure using charge coupled devise detector
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B).
  1998 - 2000
  YAMANAKA Takamitsu, NAGAI Takaya, YOSHIASA Akira, TSUNEMI Hiroshi
  The aim of the present research project aimed to investigate the structure changes and stability relations of earth's interiors under the conditions of same temperature and pressure as carth mantle and core. Dynamical structure changes under compression were observed by time-resolved diffraction experiment in time interval of second or millisecond. In order to understand the mechanism of phase transition or decomposition, we developed the single-crystal X-ray diffraction system for kinetic studies of these structure transformations. For this purpose, two-dimensional X-ray detector of charge coupled detector (CCD) was planed to be installed in the newly devised system. It enables to execute the time-resolved study. After searching the several CCD detectors made by SIMENS, NONIUS, QUANTUM and RIGAKU.The RIGAKU detector was tested from the viewpoints of dynamic range, quantum efficiency, positional resolution and reproducibility. Computer programs for driving the system and data analysis were also developed. Combined with the rotating anode X-ray generator and HUBER four-circle diffractometer facilitated in laboratory, diamond anvil high-pressure cell with electric resistance heater makes possible the diffraction study of structure transformation in the process of compression. The high-pressure and high-temperature studies up to 80GPa and 550℃ can be possible.
  The present instrumental development has already been reported in annual meeting of High-Pressure Technology and Sciences : By using the new system the following experiments are scheduled in near future.
  (1) Observation of pressure-induced amorphization, martensic structure transition, and precursor phenomenon of melting.
  (2) Time-resolving diffraction study of structure transformation including dehydration, degas, phase decomposition, radiation damage etc.
  (3) Inspection of crystallization from melts.
  (4) Perception of solid-solid reaction under compression with heating condition.
  (5) Elucidation of electronic density of state in the filed of material sciences, metallurgy, solid-state physics and several other science.
  The present detector system combined with synchrotron radiation will be an effective tool for kinetic study of structure transformation.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B)., Osaka University, 10554025
• Effective factors in the kinetics of pressure-induced transformation.
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
  1998 - 1999
  NAGAI Takaya
  The kinetics of the quartz-coesite transformation were investigated at 4 GPa and 650, 750 and 850℃ using quartz single crystal and powdered samples. Optical microscopic observations for partly transformed single crystal samples indicate that the coesite heterogeneously nucleates on the surface of the quartz grain and grows into the interior. The growth rate of coesite is independent of crystallographic orientations. The mechanism of incoherent grain-boundary nucleation and interface-controlled growth seems to operate during the transformation. The thickness of the coesite rims increases linearly as a function of time and the growth rate clearly depends on temperature. The activation energy for growth of coesite is determined as 85 (±11) kJ/mol and this value is significantly small in comparison with that determined for powdered samples.
  Synchrotron x-ray powder diffraction studies were performed on Ca(OH)ィイD22ィエD2 and Mg(OH)ィイD22ィエD2 under room temperature pressurization to 10.4 GPa and 16.0 GPa, respectively. We used the diamond anvil cells technique and the data were collected with an imaging plate detector at BL-18C in Photon Factory at KEK, Japan. The c-axis is much softer than the a-axis and, thus, the c/a ratio decreases with pressure. There is no remarkable discontinuity in the compression curves. The atomic position of O atoms, (1/3, 2/3, z), has been successfully refined using Rietveld analysis of x-ray powder diffraction patterns. In Mg(OH)ィイD22ィエD2, a change of compression mechanism is observed at 11GPa. However, in Ca(OH)ィイD22ィエD2, it is concluded that the shortening of the interlayer spacing controls compression below the amorphization pressure and no change of compression mechanism has occurred. It has been reported that H disorder occurs at a pressure in Mg(OH)ィイD22ィエD2 and the present results clearly suggest that the H disorder has great influence on the compression behavior.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Osaka University, 10640463
• Structure & physical Properties of Earth Interior at High Pressure
  Grants-in-Aid for Scientific Research Grant-in-Aid for international Scientific Research
  1996 - 1997
  YAMANAKA Takamitsu, NAGAI Takaya, OTAKA Osamu, YOSHIASA Akira, YAGI Takehiko, SHIMOMURA Osamu
  In order to comprehend the dynamics of theology, earth quake and subduction of slab in the earth crust or mantle, we investigate the phase transition and structure change of earth materials under high temperature and pressure. We have also proceed the collaboration works concerning the solid state earth science and high pressure technology with German crystallographers and mineralogists using synchrotron and neutron diffraction.
  It has been known that structure and texture changes of minerals composed of polycrystalline materials under stress field induces the solid mobility. For the purpose of understanding the above mentioned mechanical process, quantitative kinetic investigations has been undertaken by the simulation of physco-chemical process found in the earth interiors as a function of temperature, pressure, partial pressure, electric field, magnetic field and chemical potential.
  Our investigations are worth while not only for science intelligence of material structure and texture under high pressure but also for the suggestions to the analysis of the mechanism of the earth crust dynamics and mantle science.
  The present research has provided the great influence to the collaboration between German and Japanese mineral science.
  The following research projects have been performed :
  (1) Structure change with ascent and descent of earth interiors (precise measurement of intracrystalline proliferation and computer simulation as a function of pressure-temperature-time.)
  (2) Analysis of plastic and elastic deformation of crystal lattice under high pressure and temperature.
  (3) Mobility of earth materials as functions of such deriving forces as bulk modulus, viscosity, thermal expansibity, elastic velocity.
  Japan Society for the Promotion of Science, Grant-in-Aid for international Scientific Research, Osaka University, 08044082
• In situ observation and kinetics of the phase transformation under high pressure and stress
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
  1996 - 1997
  YAMANAKA Takamitsu, NAGAI Takaya, OTAKA Osamu, UEDA Chiaki, YOSHIASA Akira
  Present investigation aims to discuss the kinetics of the phase transformation of silicates and hydrates constituting earth crust and mantle. It has been known that the phase change often stays in the metastable or even unstable state by the Ostwald step rule, when the thermal energy is not large enough to supply the proper activation energy for the phase transformation. For the purpose of understanding the above mentioned mechanical process, quantitative kinetic investigations have been undertaken by the simulation of physico-chemical process found in the earth interiors as a function of temperature, pressure and stress. The following research projects have been performed :
  (1) X-ray diffraction study of the phase transition of Ca(OH)2, which is an analog material to mafic hydrates such as serpentine, has been carried out using the single crystal under hydrostatic pressure condition at 300K with diamond-avil cell (DAC). The compression induced a high density amorphous state but never brought a CaCl2 type high pressure stable phase. This pressure-induced amorphization was caused by elastic deformation of the lattice and it is a reversible transformation.
  (2) An internal Pt heating system installed in the DAC enable to simulate the more precise phase transformation in the earth mantle in consideration of the geothermal gradient. Kinetics study of the structure change from quartz to coesite under various pressures and temperatures was undertakek by the time resolved diffraction study, Their physical properties such as thermal expansibity, bulk moduli and elastic constants were observed. It has clarified that the various compression paths and heating processes bring a different threshold transition critical pressure and temperature.
  (3) The present Raman spectroscopic study and EXAFS experiment accounts for the elastic or plastic lattice deformation causes the amorphization under high pressure. The investigation of the local structure of glass and high density amorphous phase of GeO2 could explain the different mechanism of the pressure-induced amorphization.
  (4) Simulation of structure change of SiO2, GeO2, SnO2 and PbO2 having a rutile structure has been executed under variable stress field through the molecular dynamical calculation using optimized pair potential and molecular orbital calculation based on DX-Xalpha method.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Osaka University, 08640606
• 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
  科学研究費助成事業 奨励研究(A)
  1996 - 1996
  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。
  日本学術振興会, 奨励研究(A), 大阪大学, 08740413
• Evaporation Experiments on Planetary Materials.
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
  1995 - 1996
  TSUCHIYAMA Akira, NAGAI Takaya, YAMANAKA Takamitsu, UYEDA Chiaki
  It has been believed that evaporation and condensation processes playd important roles in differentiation of materials during the formation of the solar system. The following results were obtained in the present project in relation to the above topics.
  (1) Experimental techniques for exactly obtaining time variation in the amounts of evaporation and condensation by using ultra-high temperature thermal balance to discuss their kinetics strictly were developed. First of all, dehydration experiments on hydrous silicate minerals and glass were carried out, and it was confirmed that kinetics of dehydration, wthich is regarded as incongruent evaporation of water, can be discussed by time variation in the amouts of dehydration. Evaporation experiments of alkalies (Na and K) on silicate melts were carried out at low pressures, and the evaporation rates were successfully obtained.
  (2) A new model on evaporation of Na from silicate melts and origin of chondrules was proposed. It was shown that chondrule formation is possible not only by open-system flash heating mechanism which has been proposed previously but by closed-system gradual heating. This gave a new viewpoint on the chondrule formation issue.
  (3) Evaporation experiments on Fe-S minerals (metallic iron and troilite) were done, and their kinetics (modes and rates) were obtained. Evaporation rates of these minerals in the primordial solar nebula were estimated based on the present results, and the Fe/S fractionation in the primordial solar nebula was discussed by combining a model for formation of a protoplanetary disk with the evaporation data.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Osaka University, 07454132
• 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
  科学研究費助成事業 奨励研究(A)
  1995 - 1995
  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。
  日本学術振興会, 奨励研究(A), 大阪大学, 07854027
• Evaporation Experiments on Planetary Materials.
  Grants-in-Aid for Scientific Research Grant-in-Aid for General Scientific Research (C)
  1993 - 1994
  TSUCHIYAMA Akira, NAGAI Takaya, TAKUBO Hiroshi, YAMANAKA Takamitsu, MATSUDA Junichi, UEDA Chiaki
  Evaporation rates and their evaporation coefficients of important minerals forming terrestrial planets (forsterite, metallic iron, and troilite) were determined by evaporation experiments. Forsterite evaporates congruently, and the evaporation obeys a linear rate law. Its evaporation coefficient showed that the evaporation of forsterite under a H_2-rich atmosphere occurs by mechanism similar to that of free evaporation. From the results, evaporation rates of forsterite in a primordial solar nebula can be estimated. Evaporation of metallic iron also obeys a linear rate law, and its evaporation coefficient is close to unity. Incongruent evaporation of troilite with metallic iron residue obeys a linear rate law due to reaction at the troilite-metallic iron interface as a rate-determining process. From the experimental results together with previous data, evaporation rates of important minerals forming terrestrial planets were complied. Elemental fractionation (Mg/Si and Fe/S) due to evaporation of mineral dust in the primordial solar nebula was discussed based on the complied data. It was suggested that incongruent evaporation of enstatite did not occur but apparent congruent evaporation of enstatite occurred, and thus no Mg/Si fractionation is expected. However, Mg/Si fractionation is possible as long as the dust was amorphous Mg-silicate. Fe/S fractionation was expected due to incongruent evaporation of troilite. A model for isotopic mass fractionation due to evaporation of solids was also constructed based on the evaporation rates of the minerals. The fractionation depends on the evaporation rate, diffusion coefficient in the solid, the size of the solid, and isotopic fractionation factor which is determined from the mass of evaporated molecules. Based on the model, conditions for isotopic mass fractionation found in meteorites were estimated successfully.
  Japan Society for the Promotion of Science, Grant-in-Aid for General Scientific Research (C), Osaka University, 05833009
• 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
  科学研究費助成事業 一般研究(C)
  1993 - 1993
  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。
  日本学術振興会, 一般研究(C), 大阪大学, 05640531