Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of High Pressure Science and Technology  

Recent progress in theoretical mineral physics based on the ab initio quantum mechanical computation method has been dramatic in conjunction with the advancement of computer technologies. It is now possible to predict stability and several physical properties of complex minerals quantitatively not only at high pressures but also at high temperatures with uncertainties that are comparable to or even smaller than those attached in experimental data. Our present challenges include calculations of high-P,T elasticity to constrain the lower mantle mineralogy, transport properties such as lattice thermal conductivity, and further extensions to terapascal phase equilibria of Earth materials for studying planetary interiors.

DOI： 10.4131/jshpreview.30.140

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Atomic structure and lattice dynamics properties of the novel configurations of VN4 and VN4H defects in combination with the {001} platelet structure in diamond are investigated by first-principles density functional techniques. We find that incorporation of B centers (VN4) in the platelet structure substantially reduce the formation energy of B centers by ~0.45 eV for both structure models, suggesting that they may tend to develop preferentially together with platelets. Moreover, our results provide evidence that VN4 centers in the platelet might be effective sinks for atomic hydrogen in diamond. Vibrational properties of the defective structures are computed by using the linear response density functional perturbation theory (DFPT). Nsingle bondH stretching modes for VN4H centers appear around 3221 (model 1) and 3095 (model 2) cm−1, suggesting that the experimental vibrational modes of 3085.4, 3107 and 3237 cm−1 observed in natural IaA/B diamonds could be attributed to the VN4H defects. Moreover, we observed that incorporation of VN4H centers quenches the platelet IR absorption, which is unconventional but important in understanding the platelet degradation phenomenon. Our calculations shed light on possible novel configurations of VN4H centers and platelets, which can be extrapolated to VN4H2 centers as well as to a more hybrid platelet structure, and elucidate the role of nitrogen and hydrogen in the development of platelet defects in diamond.

DOI： 10.1016/j.diamond.2020.107957

researchmap

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1146/annurev-earth-071719-055139

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

The effects of light elements such as H, C, O, Si, and S on the local structures of liquid Fe under high pressure are investigated by ab initio molecular dynamics (MD) simulations. The simulations clarify that H, C, and O are incorporated into liquid Fe interstitially while Si and S are “substitutional” type impurities. From the calculated partial pair distribution functions, it is found that an interaction between light elements exists even under high‐pressure conditions exceeding 100 GPa. Additionally, the interaction depends on the type of element. The CC interactions are stronger than those of other light elements. The SS interactions depend on the S concentration, in the sense that the shape of pair distribution functions for the SS correlation changes with increasing S concentration.

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The density of liquid iron has been determined up to 116 GPa and 4350 K via static compression experiments following an innovative analysis of diffuse scattering from liquid. The longitudinal sound velocity was also obtained to 45 GPa and 2700 K based on inelastic x-ray scattering measurements. Combining these results with previous shock-wave data, we determine a thermal equation of state for liquid iron. It indicates that Earth's outer core exhibits 7.5%-7.6% density deficit, 3.7%-4.4% velocity excess, and an almost identical adiabatic bulk modulus, with respect to liquid iron.

DOI： 10.1103/PhysRevLett.124.165701

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：{MDPI} {AG}  

DOI： 10.3390/min10010054

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2018jb015857

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Potassium partitioning between molten silicates and liquid iron alloys is the fundamental process determining its incorporation into the Earth's core. In this study, it is investigated using the method of the ab initio molecular dynamics simulation combined with the thermodynamic integration technique. Results suggest that the potassium incorporation into iron alloys positively depends on temperature, while the effect of pressure is insignificant. Moreover, the existence of oxygen in liquid iron alloys significantly enhances the potassium solubility therein, whereas sulfur and silicon only have negligible effects. Electronic structure analyses reveal that potassium remains alkali‐metallic in liquid iron alloy systems under all conditions in this study, which is distinct from the characteristics reported for solid potassium. Atomic structure analyses indicate that the oxygen coordination number around potassium atom increases with oxygen concentration in liquid iron alloys, supporting the oxygen concentration dependence of the potassium partitioning between molten silicates and liquid iron alloys. Using the obtained partitioning coefficients combined with geochemical property, the maximum potassium concentration in the Earth's core is estimated to be ~30 ppm, which would be unlikely to affect the thermal evolution of the Earth's core significantly.

DOI： 10.1029/2018JB015522

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

irst-principles calculations are performed to investigate vacancy formation and migration in the B2 phase of MgO. Defect energetics suggest the importance of intrinsic non-interacting vacancy pairs, even though the extrinsic vacancy concentration might govern atomic diffusion in the B2 phase of MgO. The enthalpies of ionic vacancy migration are generally found to decrease across the B1-B2 phase transition around a pressure of 500 GPa. It is shown that this enthalpy change induces a substantial increase in the rate of vacancy diffusion in MgO of almost four orders of magnitude (∼104) when the B1 phase transforms into the B2 phase with increasing pressure. If plastic deformation is controlled by vacancy diffusion, mantle viscosity is expected to decrease in relation to this enhanced diffusion rate in MgO across the B1-B2 transition in the interior of Earth-like large exoplanets. Our results of atomic relaxations near the defects suggest that diffusion controlled creep viscosity may generally decrease across high-pressure phase transitions with increasing coordination number. Plastic flow and resulting mantle convection in the interior of these super-Earths may be therefore less sluggish than previously thought.

DOI： 10.1016/j.icarus.2017.12.020

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

The melting curve of MgO is extended up to 4 TPa, corresponding to the Jovian core pressure, based on the one-step thermodynamic integration method implemented on ab initio molecular dynamics. The calculated melting temperatures are 3100 and 16 000 K at 0 and 500 GPa, respectively, which are consistent with previous experimental results, and 20 600 K at 3900 GPa, which is inconsistent with a recent experimental extrapolation, which implies the molten Jovian core. A quite small Clapeyron slope () of is found at 3900 GPa due to comparable densities of the liquid and B2 phases under extreme compression. The Mg-O coordination number in the liquid phase is saturated at around 7.5 above 1 TPa and remains smaller than that in the B2 phase (8) even at 4 TPa, suggesting no density crossover between liquid and crystal and thus no further denser crystalline phases. Dynamical properties (atomic diffusivity and viscosity) are also investigated along the melting curve to understand these behaviors in greater detail.

DOI： 10.1088/1361-648X/aaac96

Scopus

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of High Pressure Science and Technology  

The Hugoniot of magnesium oxide (MgO) has been investigated experimentally and computationally at the pressure range between 200 GPa and 1 TPa, where B1 and B2 structures are theoretically stable and liquid exists. The shock velocity is found to be proportional with the particle velocity up to the shock velocity of 15 km s^&minus;1, suggesting MgO is in the B1 structure up to a shock pressure of ～350 GPa. Moreover, the Hugoniot data combined with <i>ab initio</i> calculations show two crossovers between the Hugoniot and an extrapolation by the linear relation around 350 GPa (and 8000 K) and 650 GPa (and 14000 K), respectively. The regions separated by the two crossovers are interpreted to be the fields of B1-B2, and B2-liquid transitions, respectively. They are consistent with the results by the <i>ab initio</i> calculations.<br>

DOI： 10.4131/jshpreview.27.137

CiNii Books

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We investigated transverse acoustic (TA) phonons in iron-bearing magnesium oxide (ferropericlase) up to 56 GPa using inelastic x-ray scattering (IXS). The results show that the energy of the TA phonon far from the Brillouin zone center suddenly increases with increasing pressure above the spin transition pressure of ferropericlase. Ab initio calculations revealed that the TA phonon energy far from the Brillouin zone center is higher in the low-spin state than in the high spin state; that the TA phonon energy depend weakly on pressure; and that the energy gap between the TA and the lowest-energy-optic phonons is much narrower in the low-spin state than in the high-spin state. This allows us to conclude that the anomalous behavior of the TA mode in the present experiments is the result of gap narrowing due to the spin transition and explains contradictory results in previous experimental studies.

DOI： 10.1088/1361-648X/aa7026

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Lattice thermal conductivity κlat of MgO at high pressures P and temperatures T up to 150 GPa and 4000 K are determined using lattice dynamics calculations and the linearized phonon Boltzmann transport equation (BTE) beyond the relaxation time approximation (RTA) from first principles. It is found that the complete solution of the linearized BTE substantially corrects values of κlat calculated with the RTA by ∼30%, from ∼42 to ∼54Wm-1K-1 under ambient conditions. The calculated values of κlat are in good agreement with those from the existing experiments. At conditions representative of the Earth's core-mantle boundary (P=136GPa and T=3800K), κlat is predicted to be ∼32 and ∼40Wm-1K-1 by RTA and the full solution of BTE, respectively. We report a detailed comparison of our study with earlier theoretical studies.

DOI： 10.1103/PhysRevB.95.184303

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Lattice thermal conductivity κlat of MgO at high pressures P and temperatures T up to 150 GPa and 4000 K are determined using lattice dynamics calculations and the linearized phonon Boltzmann transport equation (BTE) beyond the relaxation time approximation (RTA) from first principles. It is found that the complete solution of the linearized BTE substantially corrects values of κlat calculated with the RTA by ∼30%, from ∼42 to ∼54 W m−1 K−1 under ambient conditions. The calculated values of κlat are in good agreement with those from the existing experiments. At conditions representative of the Earth’s core-mantle boundary (P = 136 GPa and T = 3800 K), κlat is predicted to be ∼32 and ∼40 W m−1 K−1 by RTA and the full solution of BTE, respectively. We report a detailed comparison of our study with earlier theoretical studies.

DOI： 10.1103/PhysRevB.95.184303

Scopus

researchmap

Publishing type：Research paper (scientific journal)   Publisher：{AIP} Publishing  

© 2017 Author(s). The elastic constants of ice VIII and ice X phases under pressure have been determined at static 0 K conditions using first principles calculation. A step-like increase of the elastic constants of ice VIII phase occurred at 100-110 GPa due to hydrogen bond symmetrization. The elastic constants, and the pressure dependencies of these constants, of ice X and VIII are completely distinct. Due to these differences, these two phases can be distinguished on the basis of the elastic behavior. Conversely, the experimental elastic constant of C 11 of ice VII gradually changes from an ice VIII like asymmetric hydrogen bond to a symmetric bond character within a wide pressure range. This finding suggests that the transition from ice VII to ice X starts around 30 GPa and completes at 110 GPa.

DOI： 10.1063/1.4973339

Scopus

researchmap

Language：Japanese   Publisher：The Japan Society of High Pressure Science and Technology  

© 2017, Japan Society of High Pressure Science and Technology. All rights reserved. The Hugoniot of magnesium oxide (MgO) has been investigated experimentally and computationally at the pressure range between 200 GPa and 1 TPa, where B1 and B2 structures are theoretically stable and liquid exists. The shock velocity is found to be proportional with the particle velocity up to the shock velocity of 15 km s -1 , suggesting MgO is in the B1 structure up to a shock pressure of ~350 GPa. Moreover, the Hugoniot data combined with ab initio calculations show two crossovers between the Hugoniot and an extrapolation by the linear relation around 350 GPa (and 8000 K) and 650 GPa (and 14000 K), respectively. The regions separated by the two crossovers are interpreted to be the fields of B1-B2, and B2-liquid transitions, respectively. They are consistent with the results by the ab initio calculations.

DOI： 10.4131/jshpreview.27.137

Scopus

CiNii Books

researchmap

Publishing type：Research paper (scientific journal)  

© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. Water transported into Earth&#039;s interior by subduction strongly influences dynamics such as volcanism and plate tectonics. Several recent studies have reported hydrous minerals to be stable at pressure and temperature conditions representative of Earth&#039;s deep interior, implying that surface water may be transported as far as the core-mantle boundary. However, the hydrous mineral goethite, α-FeOOH, was recently reported to decompose under the conditions of the middle region of the lower mantle to form FeO 2 and release H 2, suggesting the upward migration of hydrogen and large fluctuations in the oxygen distribution within the Earth system. Here we report the stability of FeOOH phases at the pressure and temperature conditions of the deep lower mantle, based on first-principles calculations and in situ X-ray diffraction experiments. In contrast to previous work suggesting the dehydrogenation of FeOOH into FeO 2 in the middle of the lower mantle, we report the formation of a new FeOOH phase with the pyrite-Type framework of FeO 6 octahedra, which is much denser than the surrounding mantle and is stable at the conditions of the base of the mantle. Pyrite-Type FeOOH may stabilize as a solid solution with other hydrous minerals in deeply subducted slabs, and could form in subducted banded iron formations. Deep-seated pyrite-Type FeOOH eventually dissociates into Fe 2 O 3 and releases H 2 O when subducted slabs are heated at the base of the mantle. This process may cause the incorporation of hydrogen into the outer core by the formation of iron hydride, FeH x, in the reducing environment of the core-mantle boundary.

DOI： 10.1038/nature22823

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Association for the Advancement of Science  

Hexagonal close-packed iron (hcp-Fe) is a main component of Earth's inner core. The difference in density between hcp-Fe and the inner core in the Preliminary Reference Earth Model (PREM) shows a density deficit, which implies an existence of light elements in the core. Sound velocities then provide an important constraint on the amount and kind of light elements in the core. Although seismological observations provide density-sound velocity data of Earth's core, there are few measurements in controlled laboratory conditions for comparison. We report the compressional sound velocity (VP) of hcp-Fe up to 163 GPa and 3000 K using inelastic X-ray scattering from a laser-heated sample in a diamond anvil cell. We propose a new high-temperature Birch's law for hcp-Fe, which gives us the VP of pure hcp-Fe up to core conditions. We find that Earth's inner core has a 4 to 5% smaller density and a 4 to 10% smaller VP than hcp-Fe. Our results demonstrate that components other than Fe in Earth's core are required to explain Earth's core density and velocity deficits compared to hcp-Fe. Assuming that the temperature effects on iron alloys are the same as those on hcp-Fe, we narrow down light elements in the inner core in terms of the velocity deficit. Hydrogen is a good candidate
thus, Earth's core may be a hidden hydrogen reservoir. Silicon and sulfur are also possible candidates and could show good agreement with PREM if we consider the presence of some melt in the inner core, anelasticity, and/or a premelting effect.

DOI： 10.1126/sciadv.1500802

Scopus

researchmap

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_1500

researchmap

Web of Science

researchmap

Language：Japanese   Publishing type：Research paper (other academic)  

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The self-diffusion and tracer diffusion coefficients and viscosity of non-magnetic liquid Fe-0 alloys were determined at 100-350 GPa and 4000-8000 K on the basis of the ab initio molecular dynamics simulation method. Those of pure liquid iron are found to be consistent with the results of former studies. We confirmed that the self-diffusivity of Fe monotonically increases with increasing oxygen fraction. Meanwhile, the viscosity monotonically decreases with increasing oxygen fraction. On the other hand, the depth dependence of diffusivities and viscosity in the outer core are not great along the geotherm because pressure and temperature conversely affect the transport coefficients. The calculated diffusivity suggests that an O-rich stratified layer with a thickness of 70 km could be produced at the uppermost layer of the outer core if the layer was created from the diffusion of O from the mantle. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2015.03.006

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Magnesium oxide has been experimentally and computationally investigated in the warm-dense solid and liquid ranges from 200 GPa to 1 TPa along the principal Hugoniot. The linear approximation between shock velocity and particle velocity is validated up to a shock velocity of 15 km/s from the experimental data, this suggesting that the MgO B1 structure is stable up to the corresponding shock pressure of similar to 350 GPa. Moreover, our Hugoniot data, combined with ab initio simulations, show two crossovers between MgO Hugoniot and the extrapolation of the linear approximation line, occurring at a shock pressures of approximately 350 and 650 GPa, with shock temperatures of 8000 and 14 000 K, respectively. These crossover regions are consistent with the solid-solid (B1-B2) and the solid-liquid (B2-melt) phase boundaries predicted by the ab initio calculations.

DOI： 10.1103/PhysRevE.92.023103

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The physical state and properties of silicates at conditions encountered in the cores of gas giants, ice giants, and of Earth-like exoplanets now discovered with masses up to several times the mass of the Earth remain mostly unknown. Here, we report on theoretical predictions of the properties of silica, SiO2, up to 4 TPa and about 20 000 K by using first principles molecular dynamics simulations based on density functional theory. For conditions found in the super Earths and in ice giants, we show that silica remains a poor electrical conductor up to 10 Mbar due to an increase in the Si-O coordination with pressure. For Jupiter and Saturn cores, we find that MgSiO3 silicate has not only dissociated into MgO and SiO2, as shown in previous studies, but that these two phases have likely differentiated to lead to a core made of liquid SiO2 and solid (Mg,Fe)O.

DOI： 10.1103/PhysRevB.92.014105

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

The dominant minerals in Earth's lower mantle are thought to be Fe- and Al-bearing MgSiO3 bridgmanite and (Mg, Fe)O ferropericlase(1). However, experimental measurements of the elasticity of these minerals at realistic lower-mantle pressures and temperatures remain impractical. As a result, different compositional models for the Earth's lower mantle have been proposed(2-4). Theoretical simulations, which depend on empirical evaluations of the effects of Fe incorporation into these minerals, support a pyrolitic lower mantle that contains a significant amount of ferropericlase(5,6), much like the Earth's upper mantle. Here we present first-principles computations combined with a lattice dynamics approach that include the effects of Fe2+ and Fe3+ incorporation. We calculate the densities and elastic-wave velocities of several possible lower-mantle compositions with varying amounts of ferropericlase along a mantle geotherm. On the basis of our calculations of aggregate elasticities, we conclude that neither a perovskitic composition (about 9:1 bridgmanite to ferropericlase by volume) nor an olivine-like composition (about 7:3) reproduces the seismological reference model of average Earth properties. However, an intermediate volume fraction (about 8:2) consistent with a pyrolitic composition can reproduce the reference velocities and densities. Bridgmanite that is rich in ferric iron produces the best fit. Our findings support a uniform chemical composition throughout the present-day mantle, which we suggest is the result of whole-mantle convection.

DOI： 10.1038/NGEO2458

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Ca-perovskite (CaPv) is considered to be one of the most abundant minerals in the Earth's lower mantle (LM). Furthermore, previous static calculations and mean-field theory suggest that it has a much larger shear modulus than bridgmanite (MgPv). In this study, the elasticity of cubic CaPv was reinvestigated using the density functional constant-temperature first principles molecular dynamics method under the correct conditions to simulate its elasticity. Our new results clearly demonstrate that cubic CaPv has comparable bulk and slightly smaller shear moduli than Fe-bearing MgPv. This is because the boundary condition for the supercell used in this study allows for the rotational phonon motion of SiO6 octahedra under strain, which predominantly affects the decrease in C-11 and C-44. Acoustic wave velocities determined from the elastic moduli indicate that cubic CaPv has slower velocities and larger densities than Fe-bearing MgPv and preliminary reference Earth model in the LM. This suggests that if CaPv-rich material exists, it can accumulate in the lowermost LM and produce a seismically low-velocity anomaly.

DOI： 10.1002/2015GL063446

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We study the high-pressure stability and elastic properties of Mg3Al2Si3O12 Pyrope garnet using the density functional first principles computation method. Pyrope garnet is found to dissociate into an assemblage of MgSiO3 Mg-perovskite (Pv) and Al2O3 corundum (Cor) solid solutions at similar to 19.7 GPa at static conditions. Then, this assemblage undergoes a phase transition to pyropic (Al-bearing) Pv at similar to 65 GPa. The enthalpy of an assemblage of MgAl2O4 calcium ferrite (CF), MgPv, and stishovite (St) is less stable than that of MgPv plus Cor. A continuous reaction in the MgSiO3-Al2O3 system suggested by this study is consistent with previous experimental and computational studies but not with a recently modeled phase diagram. This implies that the formation of pyropic Pv could not cause any seismic scatterers in the mid-lower mantle. The investigated anisotropy of elastic velocities further indicates that pyrope garnet is a very isotropic mineral. Our results suggest that seismological anisotropy inferred in the upper mantle could not be due to garnet. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2014.10.005

Web of Science

Scopus

researchmap

Language：English   Publishing type：Part of collection (book)   Publisher：Springer International Publishing  

The fate and amount of granitic materials subducted into the deep mantle are still under debate. The density, elastic property, and phase stability of granitic materials in the mantle pressures are key to clarifying them. Here, we modeled highpressure properties of the granitic assemblage by using ab initio mineral physics data of grossular garnet, K-hollandite, jadeite, stishovite, and calcium ferrite (CF)-type phase. We find that the ongoing subducting granitic assemblage, such as sediments and average upper crust rocks, is much denser than pyrolite in the pressure range from 9 GPa (~270 km), at which coesite undergoes a phase transition to stishovite, to around 27 GPa (~740 km). Above this pressure, granitic material becomes less dense than a pyrolite. This indicates that the granitic assemblage becomes gravitationally stable at the base of the mantle transition zone (MTZ). Results suggest a possibility that the granitic materials could accumulate around the 740 km depth if carried into the depth deeper than 270 km and segregated at some depth. Comparison of the velocities between granitic and pyrolitic materials shows that granitic materials can produce substantial velocity anomalies in the MTZ and the uppermost lower mantle (LM). Seismic observations such as anomalously fast velocities, especially for the shear wave, around the 660-km discontinuity, the complexity of 660-km discontinuity, and the scatterers in the uppermost LM could be associated with the subducted granitic materials.

DOI： 10.1007/978-3-319-15627-9_8

Web of Science

Scopus

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

J-GLOBAL

researchmap

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_1756

CiNii Books

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The postperovskite phase of ZnGeO3 was confirmed by laser heating experiments of the perovskite phase under 110-130 GPa at high temperature. Ab initio calculations indicated that the phase transition occurs at 133 GPa at 0 K. This postperovskite transition pressure is significantly higher than those reported for other germanates, such as MnGeO3 and MgGeO3. The comparative crystal chemistry of the perovskite-to-postperovskite transition suggests that a relatively elongated b-axis in the low-pressure range resulted in the delay in the transition to the postperovskite phase. Similar to most GdFeO3-type perovskites that transform to the CaIrO3-type postperovskite phase, ZnGeO3 perovskite eventually transformed to the CaIrO3-type postperovskite phase at a critical rotational angle of the GeO6 octahedron. The formation of the postperovskite structure at a very low critical rotational angle for MnGeO3 suggests that relatively large divalent cations likely break down the corner-sharing GeO6 frameworks without a large rotation of GeO6 to form the postperovskite phase.

DOI： 10.1021/ic501958y

Web of Science

PubMed

researchmap

Language：Japanese  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

We systematically investigated the L-edge X-ray emission spectroscopy (XES), a 3d-to-2p transition, of Fe2+- and Fe3+-bearing MgSiO3 perovskite under high pressure based on the internally consistent LSDA+U technique combined with the Slater-transition method. The Fe L-edge XES spectra can be used to directly interpolate the distribution of Fe-3d electrons including the spin states and coordination environments of iron. Our results show that the spin transition from the high-spin state to low-spin state of Fe2+ and Fe3+ can be identified easily by the L-edge XES technique. The valence state of Fe (2+ or 3+) can be verified by this, since a shift of the first main peak of Fe2+ across the spin transition of 2 eV, in good agreement with the experimental value (similar to 1.6 eV), is significantly smaller than that of Fe3+ of 4 eV. The width of the L-edge XES of Fe3+ also depends strongly on the substitution sites (Mg or Si), meaning that its coordination environments might also be distinguishable based on the Fe L-edge XES spectra. These strong sensitivities to the Fe's states suggest that the high-resolution Fe L-edge XES would be a useful experimental technique to investigate Fe-bearing silicate minerals.

DOI： 10.2138/am.2014.4518

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

The equation of state (EoS) and thermodynamic properties of non-magnetic liquid iron were investigated from energy (E)-pressure (P)-volume (V)-temperature (T) relationships calculated by means of ab initio molecular dynamics simulations at 60-420 GPa and 4000-7000K. Its internally consistent thermodynamic and elastic properties, in particular, density, adiabatic bulk modulus, and P wave velocity, were then analyzed. Compared to the seismological data of the Earth's outer core, pure liquid iron is found to have an 8-10% larger density and 3-10% larger bulk modulus than the Earth's values. Results also show that the P wave velocity of liquid iron has marginal temperature dependence as the bulk sound velocity of solid iron. The new EoS model and thermodynamic properties of liquid iron may serve as fundamental data for the thermochemical modeling of the Earth's core.

DOI： 10.1002/2013JB010732

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

Ca-perovskite (Pv) is considered to be one of the most abundant minerals in the Earth's lower mantle (LM) with an ideal cubic structure at LM pressures and temperatures. In this study, a pressure-volume-temperature (P-V-T) equation of state model for Ca-Pv is constructed using density functional first-principles molecular dynamics simulations. The calculated P-V-T data yield KT01000K = 203.95 GPa, V01000K = 46.17 Å3/formula unit, γ0 = 1.576, and q = 0.96 within the framework of the Mie-Grüneisen-Debye formulation. We compare the density and bulk sound velocity of Ca-Pv with those of iron-bearing Mg-Pv and seismological values. Along an adiabatic temperature gradient, Ca-Pv has ~2.5% higher density and ~0.7% faster bulk sound velocity than the preliminary reference Earth model, while it has ~3.8% higher density and ~2.7% slower bulk sound velocity than iron-bearing Mg-Pv. Our results indicate that a possible lateral variation in the Ca-Pv fraction in the LM could produce an anticorrelation between V Φ and ρ. ©2014. American Geophysical Union. All Rights Reserved.

DOI： 10.1002/2013JB010905

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

The crystal structure of a high-pressure phase of calcium hydroxide, Ca(OH)(2) (portlandite), was clarified for the first time using the combination of in situ single-crystal and powder X-ray diffraction measurements at high pressure and room temperature. A diamond-anvil cell with a wide opening angle and cell-assembly was improved for single-crystal X-ray diffraction experiments, which allowed us to successfully observe Bragg reflections in a wide range of reciprocal space. The transition occurred at 6 GPa and the crystal structure of the high-pressure phase was determined to be monoclinic at 8.9 GPa and room temperature [I121; a = 5.8882(10), b = 6.8408(9), c = 8.9334(15) angstrom, beta = 104.798(15)degrees]. The transition involved a decrease in molar volume by approximately 5.8%. A comparison of the structures of the low- and high-pressure phases indicates that the transition occurs by a shift of CaO6 octahedral layers in the a-b plane along the a-axis, accompanied by up-and-down displacements of Ca atoms from the a-b plane. The crystal structure of this high-pressure phase is considered to be an intermediate state between the low-pressure phase and the high-pressure-high-temperature phase. The complicated diffraction patterns of the high-pressure phase suggest that the phase transition occurred toward three directions around the c-axis of the low-pressure phase. This explains the difficulties encountered in previous structural analyses. The present results will provide key information for discussing the behavior of hydrogen bonds in these hydrous minerals under pressure.

DOI： 10.2138/am.2013.4386

Web of Science

researchmap

Language：Japanese   Publisher：The Japan Society of High Pressure Science and Technology  

Recent progress in theoretical mineral physics based on the <i>ab initio</i> quantum mechanical computation method has been dramatic in conjunction with the advancement of computer technologies. It is now possible to predict stability and several physical properties of complex minerals quantitatively not only at high pressures but also at high temperatures with uncertainties that are comparable to or even smaller than those attached in experimental data. Our present challenges include calculations of high-<i>P</i>,<i>T</i> elasticity to constrain the lower mantle mineralogy, transport properties such as lattice thermal conductivity, and further extensions to terapascal phase equilibria of Earth materials for studying planetary interiors.<br>

DOI： 10.4131/jshpreview.23.103

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/10020487019?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHINA UNIV GEOSCIENCES, BEIJING  

The Earth was born from a giant impact at 4.56 Ga. It is generally thought that the Earth subsequently cooled, and hence shrunk, over geologic time. However, if the Earth's convection was double-layered, there must have been a peak of expansion during uni-directional cooling. We computed the expansion-contraction effect using first principles mineral physics data. The result shows a radius about 120 km larger than that of the present Earth immediately after the consolidation of the magma-ocean on the surface, and subsequent shrinkage of about 110 km in radius within about 10 m.y., followed by gradual expansion of 11 km in radius due to radiogenic heating in the lower mantle in spite of cooling in the upper mantle in the Archean. This was due to double-layered convection in the Archean with final collapse of overturn with contraction of about 8 km in radius, presumably by the end of the Archean. Since then, the Earth has gradually cooled down to reduce its radius by around 12 km. Geologic evidence supports the late Archean mantle overturn ca. 2.6 Ga, such as the global distribution of super-liquidus flood basalts on nearly all cratonic fragments (&gt;35 examples). If our inference is correct, the surface environment of the Earth must have undergone extensive volcanism and emergence of local landmasses, because of the thin ocean cover (3-5 km thickness). Global unconformity appeared in cratonic fragments with stromatolite back to 2.9 Ga with a peak at 2.6 Ga. The global magmatism brought extensive crustal melting to yield explosive felsic volcanism to transport volcanic ash into the stratosphere during the catastrophic mantle overturn. This event seems to be recorded by sulfur mass-independent fractionation (SMIF) at 2.6 Ga. During the mantle overturn, a number of mantle plumes penetrated into the upper mantle and caused local upward doming of by ca. 2-3 km which raised local landmasses above sea-level. The consequent increase of atmospheric oxygen enabled life evolution from prokaryotes to eukaiyotes by 2.1 Ga, or even earlier in the Earth history. (C) 2013, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.gsf.2013.11.008

Web of Science

researchmap

Language：English  

researchmap

Language：English   Publishing type：Part of collection (book)   Publisher：John Wiley and Sons  

Recent progress in theoretical mineral physics based on the ab initio quantum mechanical computation method has been dramatic in conjunction with the rapid advancement of computer technologies. This chapter briefly reviews recent progress in studying high-pressure elasticity of lower mantle minerals including silicates, oxides, and some hydrous phases, and then summarizes current knowledge on the aggregate elasticity of representative lithology closely related to the mantle and slab materials. The analyses presented in the chapter indicate that the pyrolitic composition can describe the Earth's properties quite well in terms of density, P and S wave velocity, and bulk sound velocity. The overall agreements are better than those expected in more silicic compositions. Computations also suggest that cumulated basaltic piles are unsuitable to explain the LLSVP. © 2013 John Wiley &amp
Sons, Ltd.

DOI： 10.1002/9781118529492.ch7

Scopus

researchmap

Language：Japanese   Publishing type：Research paper (other academic)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

High-pressure (P) and high-temperature (T) thermodynamics and spin transition of Fe3+-bearing MgSiO3 perovskite (Pv) are investigated by means of the internally consistent LDA + U method combined with the lattice dynamics method. Fe3+ is found to contribute mainly to the low frequency phonons. The spin transition of iron in the B site occurs at 55 GPa at 300 K and from ~75 to ~90 GPa at lower mantle temperatures. Although high-spin Fe3+ expands the volume of Pv, most of the bulk thermodynamic properties of Pv are insensitive to Fe3+ incorporation at least at XFe2O3 = 0.0625, with the exception of the Grüneisen parameter. The calculated properties are in good agreement with room temperature experimental data, but a significant increase suggested in the isothermal bulk modulus is not predicted. Results clearly demonstrate that Fe3+-bearing perovskite alone does not reproduce the density and the bulk sound velocity of the Earth's lower mantle simultaneously. Key Points The spin transition of Fe3+ in Pv occurs from ~75 GPa to ~90 GPa at ~2000 K Most of the thermodynamic properties of Pv are insensitive to Fe3+ Fe3+-bearing Pv alone does not reproduce the Earth's rho and Vf simultaneously ©2012. American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JB009696

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN ACAD  

We investigate the shear response of possible slip systems activated in pure and Fe-bearing MgSiO3 post-perovskite (PPv) through ab initio generalized stacking fault (GSF) energy calculations. Here we show that the [100](001) slip system has the easiest response to plastic shear among ten possible slip systems investigated. Incorporation of Fe2+ decreases the strength of all slip systems but does not change the plastic anisotropy style. Therefore, pure and Fe-bearing MgSiO3 PPv should demonstrate similar LPO patterns with a strong signature of the [100](001) slip system. An aggregate with this deformation texture is expected to produce a V-SH &gt; V-SV type polarization anisotropy, being consistent with seismological observations.

DOI： 10.2183/pjab.89.51

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHINA UNIV GEOSCIENCES, BEIJING  

It has been thought that granitic crust, having been formed on the surface, must have survived through the Earth's evolution because of its buoyancy. At subduction zones continental crust is predominantly created by arc magmatism and is returned to the mantle via sediment subduction, subduction erosion, and continental subduction. Granitic rocks, the major constituent of the continental crust, are lighter than the mantle at depths shallower than 270 km, but we show here, based on first principles calculations, that beneath 270 km they have negative buoyancy compared to the surrounding material in the upper mantle and transition zone, and thus can be subducted in the depth range of 270-660 km. This suggests that there can be two reservoirs of granitic material in the Earth, one on the surface and the other at the base of the mantle transition zone (MTZ). The accumulated volume of subducted granitic material at the base of the MTZ might amount to about six times the present volume of the continental crust. Our calculations also show that the seismic velocities of granitic material in the depth range from 270 to 660 km are faster than those of the surrounding mantle. This could explain the anomalous seismic-wave velocities observed around 660 km depth. The observed seismic scatterers and reported splitting of the 660 km discontinuity could be due to jadeite dissociation, chemical discontinuities between granitic material and the surrounding mantle, or a combination thereof. (C) 2012, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.gsf.2012.08.003

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

To understand the fate of the host phase for potassium subducted into the deep Earth's interior, we have studied the high-pressure stability and elastic properties of KAlSi3O8 hollandite (K-hollandite) by means of the first-principles computation method. Based on experimental observations, the tetragonal K-hollandite I phase was found to undergo a ferroelastic second-order phase transition to the monoclinic K-hollandite II phase at 14.9 GPa. This K-hollandite II phase was mechanically stable up to 150 GPa (i.e., entirely in the Earth's lower mantle), being consistent with previous studies. The Born's elastic stability criteria indicate that the tetragonal mechanical instability occurs at similar pressure of 16.9 GPa with shear softening. This causes anomalous pressure dependence of the wave velocities across the instability. Taking a Clapeyron slope of 7 MPa/K and a temperature of 1800 K, the transition pressure becomes similar to 28 GPa corresponding to about 770 km depth, which would be seismologically detectable and could be comparable to seismic scatterers observed at the shallowest lower mantle. Next, we studied the solid-solution effect of sodium to K-hollandite, indicating that it is very limited on the phase stability, although the Na-end-member phase was found to be metastable. Elasticity demonstrates strong anisotropy around 15 GPa due to its ferroelastic nature.

DOI： 10.2138/am.2013.4077

Web of Science

researchmap

Publishing type：Research paper (scientific journal)  

The lattice thermal conductivity (κlat) of MgSiO 3 perovskite (Mg-Pv) under high-pressure and high-temperature conditions was computed based on the ab initio anharmonic lattice dynamics method with the density functional perturbation theory. κlat of Mg-Pv is found to increase with increasing pressure from 9.8 (at 23.5 GPa) to 43.6 W m-1 K-1 (at 136 GPa) at 300 K, while decreasing with increasing temperature from 28.1 (at 300 K) to 2.3 W m-1 K -1 (at 4000 K) at 100 GPa. A multiphase composite average yielded a mantle Rayleigh number adequate to promote the vigorous thermal convection of the mantle that is expected geophysically. © 2013 American Physical Society.

DOI： 10.1103/PhysRevLett.110.025904

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Post-Perovskite: The Last Mantle Phase Transition  

A high-pressure phase transition in iron free MgSiO3 perovskite (pv), the most abundant Earth forming mineral phase, was discovered and reported in 2003- 2004. A subsequent dissociation transition in the newly found polymorph was predicted in 2006. Here, we summarize our theoretical and computational studies of these phase transitions and of the physical properties of the newly found postperovskite (ppv) and post-ppv phases. Our approach is based on density functional theory, on the plane-wave pseudopotential method, and on quasiharmonic free energy computations. We focus here on the structural, vibrational, and thermodynamic properties, and on the stability field of the ppv phase. The predicted Clapeyron slope of the ppv transition and several properties of the ppv phase strongly suggest that this is an important candidate for a primary constituent in D&quot;. We also review the post-ppv transition and the properties of the resulting aggregate. They are important for modeling and advancing our understanding of the mantle of terrestrial exoplanets and of the gas giants&#039; cores.

DOI： 10.1029/174GM08

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Vibrational densities of states and phonon dispersion relations for Mg0.875Fe0.125O ferropericlase in the high- and low-spin (HS and LS) states were calculated from first principles lattice dynamics using the internally consistent LDA+U technique. Finite-temperature thermodynamic properties were determined based on the quasi-harmonic approximation including the HS and LS mixing entropy and the magnetic entropy effects, which gave pressure and temperature variations of the low-spin fraction. Our results suggest that for thermodynamic modeling of the earth's interior, the effect of the mixed spin state cannot be ignored in the lower mantle, especially the lowermost part. The anomaly in the seismic wave velocity due to the spin crossover transition of ferropericlase, if it exists, is difficult to detect because of the wide pressure range of the transition, which is broadened by the temperature effect and the damping of the amplitude of the slow seismic wave. Citation: Fukui, H., T. Tsuchiya, and A. Q. R. Baron (2012), Lattice dynamics calculations for ferropericlase with internally consistent LDA+U method, J. Geophys. Res., 117, B12202, doi: 10.1029/2012JB009591.

DOI： 10.1029/2012JB009591

Web of Science

researchmap

Other Link： http://orcid.org/0000-0002-7880-635X

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The thermodynamic properties of (Mg0.9375Fe2+0.0625)SiO3 perovskite have been investigated at the pressure and temperature conditions of the lower mantle by first-principles calculations where iron is incorporated in the high and low-spin states for the first time. The electronic structure of ferrous Fe-bearing perovskite is modelled within the internally consistent local spin density approximation with a Hubbard correction U. The thermodynamic properties are derived from the calculation of the Helmholtz free energy within the quasi-harmonic approximation, which requires the phonon frequencies determined by direct calculations of the dynamic matrices. Incorporation of iron, irrespective of its spin states, decreases the acoustic phonon mode frequencies, but less affects high-energy optic modes, leading to decreasing of the acoustic wave velocities in Fe-bearing MgSiO3 perovskite, consistent with previous studies on the elasticity of this phase. This study suggests that the thermodynamic properties of silicate perovskite, such as the equation of state and isothermal bulk modulus, are not largely modified by the incorporation of 6.25 per cent of ferrous iron. Calculations of the static enthalpy of the iron-bearing perovskite in the 0150-GPa-pressure range demonstrate that low-spin ferrous iron is unstable at the pressure conditions of the lower mantle. Finally, we clarify the perovskite-to-post-perovskite phase transition boundary in an (Mg0.9375Fe0.0625)SiO3 composition. Ferrous iron is found to decrease the transition pressure between the two phases with a small binary phase loop of 34 GPa at the lowermost mantle conditions from 111 to 115 GPa at 2500 K and from 116 to 119 GPa at 3000 K.

DOI： 10.1111/j.1365-246X.2012.05511.x

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Vibrational density of states of the NaAlSi2O6 jadeite and NaAlSiO4 calcium ferrite (CF)-type, and SiO2 stishovite is calculated as a function of pressure up to 50 GPa using density functional perturbation theory. The calculated frequencies are used to determine the thermal contribution to the Helmholtz free energy within the quasi-harmonic approximation and to derive the equation of state and several thermodynamic properties of interest. A dissociation of jadeite into a mixture of a CF-type phase and stishovite is predicted to occur at 23.4 GPa and 1,800 K with a positive Clapeyron slope of 2.8 MPa/K. Elastic anisotropy for jadeite, the CF-type phase, and stishovite also computed clearly shows that stishovite and the CF-type phase are the most anisotropic and isotropic in these three phases, respectively.

DOI： 10.1007/s00269-012-0485-0

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

In this study, we report the elastic properties of three ultrahigh-pressure phases of SiO2: pyrite, cotunnite and Fe2P types between 300 and 1,500 GPa calculated by means of the density functional ab initio method. It is generally thought that materials tend to be more compact and isotropic with increasing pressure. These three ultrahigh-pressure phases of silica are mechanically stable in the investigated pressure range according to the Born criteria, while the cotunnite and Fe2P types are unstable at lower pressure. The elastic azimuthal anisotropy of these ultrahigh-pressure phases of silica shows that all the structures counterintuitively have considerable anisotropies even at multimegabar pressures. Among the three investigated structures, the cotunnite type of SiO2 is the most elastically anisotropic phase due to a soft compression along the b axis combined with a large distortion of the polyhedrons that make the structure. This might also be related to its thermodynamic unfavorability compared to the Fe2P type under extreme pressure condition. The bond property analyses clearly show that the Si-O bond remains an ionic-covalent mixed bond even at multimegabar pressures with an invariable ionicity with pressure. This argument can explain the monotonously pressure dependence of the elastic anisotropy in the case of pyrite, while the changes in the velocity distribution patterns out of the thermodynamic instability range largely contribute to those of the cotunnite and Fe2P types.

DOI： 10.1007/s00269-011-0473-9

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

New hexagonal aluminous (NAL) phase and orthorhombic calcium-ferrite (CF) type phase are considered to be major mantle components of the mid-ocean ridge basalt (MORB) at pressure and temperature conditions in the lower mantle, which can potentially host alkali elements with large ionic radii. The high-pressure stability and elastic properties of both NAL and CF phases are therefore of fundamental importance for understanding the fate of subducted MORB. Here we report those properties of the NaMg2Al5SiO12 system studied by means of the first-principles computation method. NAL was found to transform to the CF phase at 39.6 G Pa, accompanied by discontinuities in density (+1.8%), as well as compressional wave (-0.2%), shear wave (+0.9%), and bulk sound (-1.0%) velocities. The property of subducted MORB was evaluated using these results, and the velocity contrast between pyrolite and MORB of similar to-5% was found to be quite comparable to the shear velocity anomaly observed for seismic scatterers at depths from 1100 to 1800 km. However, since the transformation of the NAL to CF phase within MORB produces insignificant increases in the seismic velocities, it would be seismologically undetectable. On the other hand, the anisotropy change associated with the phase transition is significant and could be seismically detectable using observations such as shear wave splitting measurements since the CF phase is considerably more anisotropic compared to the NAL phase.

DOI： 10.2138/am.2012.3915

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

In order to understand the fate of subducted continental materials by means of mechanisms such as tectonic erosion and sediment subduction, it is important to understand the high-pressure stability and elastic properties of grossular garnet. We study these questions using the first principles computation method. Grossular garnet was found to dissociate into an assemblage of CaSiO3 Ca-perovskite (Pv) and Al2O3 corundum (Cor) at about 23.4 GPa, accompanied by remarkable jumps of compressional wave (8.0%), shear wave (11.6%), bulk sound (5.7%) velocities, and density (12.1%). Although Pv with the grossular garnet composition was suggested experimentally after the decomposition reaction, this phase was found to be less stable than an assemblage of CaPv and Cor at pressures higher than 20 GPa. This indicates that observed Pv with the grossular garnet composition is metastable but can be obtained because of the slow kinetics of the garnet decomposition reaction. Our results imply that the dissociation of grossular garnet (as well as that of jadeite) included in continental materials subducted into the deep mantle increases the complexity of the 660 km discontinuity and can explain seismically observed multiple reflections. We have also investigated the anisotropy of elastic velocities of grossular garnet, CaPv, and Cor and found that CaPv is the most anisotropic mineral. This implies that CaPv could produce seismic anisotropy in the uppermost lower mantle.

DOI： 10.1029/2011JB008529

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The origin of the large low velocity structures observed in the lowermost mantle is still unclear. To make new insights into deep mantle heterogeneity, we performed ab initio modeling of the elasticity of representative petrology with the pyrolitic and basaltic compositions based on the elasticities of the following mineral phases: magnesium silicate perovskite (post-perovskite), ferropericlase, calcium silicate perovskite, stishovite (CaCl2), and calcium ferrite (titanate)-type MgAl2O4. Calculations elucidated that the basalt composite is similar to 2% denser than the pyrolitic one through all of the pressures in the lower mantle. In addition, the shear (V-S) and bulk sound (V-Phi) velocities were found to be similar to 2% slower and faster in the basalt composition in particular at similar to 30 GPa and &gt;120 GPa respectively, while both the pyrolitic and basaltic composites have almost the same compressional wave speed (V-P). Thermochemically distinct piles which are thought to be related to accumulated hot and dense subducted crusts would therefore be expected to produce as much as a -5% to -6% low velocity anomaly in the S wave but only similar to-1% in the P wave. These suggest that the basaltic pile seems less compatible to the seismological signatures of the large low velocity structures, if accompanied by thermal anomalies reaching +1000 to +1500 K. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2011.06.018

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Phonon dispersion relations and vibrational density of states of (Mg0.9375Fe0.0625)SiO3 postperovskite have been determined by direct first-principles calculations of the dynamical matrix up to 150 GPa. Incorporation of iron in the postperovskite phase, irrespective of the two investigated configurations and the spin state, was found to decrease the acoustic phonon frequencies but to have a minor effect on the optic modes at high frequencies. The phonon dispersion curves exhibit negative phonon frequencies below 10 GPa when iron is incorporated in the high or low spin state and indicate unstable dynamic structures. Then, the calculated phonon frequencies of dynamically stable structures are used to determine vibrational contributions to the Helmholtz free energy within the quasi-harmonic approximation. The high temperature equation of state and several thermodynamic properties are then derived for (Mg0.9375Fe0.0625)SiO3 postperovskite and compared with those of pure MgSiO3 postperovskite. The results show that a low concentration of iron, irrespective of high spin or low spin, in MgSiO3 postperovskite has a minor effect on the thermodynamic properties at pressure-temperature conditions of the lowermost part of the Earth's mantle.

DOI： 10.1029/2010JB008018

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have carried out in situ X-ray diffraction experiments on the FeS-H system up to 16.5 GPa and 1723 K using a Kawai-type multianvil high-pressure apparatus employing synchrotron X-ray radiation. Hydrogen was supplied to FeS from the thermal decomposition of LiAIH(4), and FeSH(x), was formed at high pressures and temperatures. The melting temperature and phase relationships of FeSH(x) were determined based on in situ powder X-ray diffraction data. The melting temperature of FeSH(x) was reduced by 150-250 K comparing with that of pure FeS. The hydrogen concentration in FeSH(x) was determined to be x = 0.2-0.4 just before melting occurred between 3.0 and 16.5 GPa. It is considered that sulfur is the major light element in the core of Ganymede, one of the Galilean satellites of Jupiter. Although the interior of Ganymede is differentiated today, the silicate rock and the iron alloy mixed with H(2)O, and the iron alloy could react with H(2)O (as ice or water) or the hydrous silicate before the differentiation occurred in an early period, resulting in a formation of iron hydride. Therefore, Ganymede&apos;s core may be composed of an Fe-S-H system. According to our results, hydrogen dissolved in Ganymede&apos;s core lowers the melting temperature of the core composition, and so today, the core could have solid FeSH(x) inner core and liquid FeH(x)-FeSH(x) outer core and the present core temperature is considered to be relatively low. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2010.10.033

Web of Science

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1073/pnas.1013594108

Scopus

PubMed

researchmap

Language：Japanese   Publisher：The Crystallographic Society of Japan  

<i>Ab intitio</i> mineral physics simulations discovered several novel phase transitions in major Earth and planetary materials under (multi) megabar pressure conditions. Here we report some recent remarks on the ultrahigh-pressure structure search of some important oxides and silicates.

DOI： 10.5940/jcrsj.53.2

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00365538323?from=CiNii

Language：Japanese   Publisher：Tokyo Geographical Society  

Recent progress in our understanding of the consuming plate boundary indicates the ubiquitous occurrence of tectonic erosion of the hanging wall of the continental margin, sediment-trapped subduction, and direct subduction of immature oceanic arcs into deep mantle. Geological studies have estimated the volume of subducted tonalite-trondhjemite-granodiorite (TTG) materials to about seven times the surface total volume of continental crust. To reveal the fate of subducted crusts and how they recycle within the Earth, we studied high-pressure densities and elastic properties of TTG by means of the first principles computation method and compared them to those of peridotite. We found that TTG is gravitationally stable and its seismic velocities are remarkably faster than peridotite in the depth range from 300 to 800 km, especially from 300 to 670 km. We, therefore, propose SiO₂-rich second continents in the mantle transition zone, which used to form the TTG crust on the Earth's surface. Our proposed model may provide reasonable explanations of seismological observations such as the splitting of the 670 km discontinuity and seismic scatterers in the uppermost part of the lower mantle. The difference in seismic velocities between PREM model and experimental results in the lower part of the transition zone can be explained by 25 volumetric% of TTG, which would correspond to about six times the present volume of the continental crust. Formation and dynamics of those second continents would have controlled the Earth's thermal history over geologic time.

DOI： 10.5026/jgeography.119.1197

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00363046813?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.83.139903

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevLett.107.045701

Scopus

researchmap

Language：English  

Solving enigmas of the Earth's inner core is a grand challenge in mineral physics, and first-principles studies play a significant role for our understanding. Iron is expected to be a major component of the inner core, and first principles calculations have shed new light on the stable crystal structure and elasticity of iron at the inner core conditions. In this article, reviewing recent first-principles studies, we discuss the stable crystal structure and the elasticity of pure iron at the inner conditions, the effect of light element on them, and an outlook for the future direction.

DOI： 10.4131/jshpreview.21.69

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.83.212101

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.83.134114

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.83.054115

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHINA UNIV GEOSCIENCES, BEIJING  

Ab initio two-phase molecular dynamics simulations were performed on silica at pressures of 20-160 GPa and temperatures of 2 500-6 000 K to examine its solid-liquid phase boundary. Results indicate a melting temperature (T-m) of 5 900 K at 135 GPa. This is 1 100 K higher than the temperature considered for the core-mantle boundary (CMB) of about 3 800 K. The calculated melting temperature is fairly consistent with classical MD (molecular dynamics) simulations. For liquid silica, the O-O coordination number is found to be 12 along the T-m and is almost unchanged with increasing pressure. The self-diffusion coefficients of O and Si atoms are determined to be 1.3x10(-9)-3.3x10(-9) m(2)/s, and the viscosity is 0.02-0.03 Pas along the T-m. We find that these transport properties depend less on pressure in the wide range up of more than 135 GPa. The eutectic temperatures in the MgO-SiO2 systems were evaluated and found to be 700 K higher than the CMB temperature, though they would decrease considerably in more realistic mantle compositions.

DOI： 10.1007/s12583-010-0126-9

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Subducted crusts contain aluminous phases with incompatible elements such as sodium. In order to understand the fate of subducted crusts and how they recycle within the Earth, it is important to investigate high-pressure stability and elastic properties of host phases. Here we have studied NaAlSi2O6 jadeite, a NaAlSiO4 calcium ferrite (CF)-type phase, and SiO2 stishovite by means of a first principles computation method. Jadeite was found to dissociate into an assemblage of the CF-type phase and stishovite at about 18 GPa, associated with remarkable increases of compressional wave (18.7%), shear wave (26.4%), bulk sound (13.3%) velocities, and density (15.1%). Proximity of this transition condition to the 660 km discontinuity in the mantle transition zone suggests that seismically observed splitting of the reflection could be related to this phase transition, implying subduction of crustal materials down to the mantle transition zone. Citation: Kawai, K., and T. Tsuchiya (2010), Ab initio investigation of high-pressure phase relation and elasticity in the NaAlSi2O6 system, Geophys. Res. Lett., 37, L17302, doi: 10.1029/2010GL044310.

DOI： 10.1029/2010GL044310

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

In situ X-ray diffraction experiments and ab initio calculations elucidated the high-pressure phase transition properties of yttrium sesquioxides. The C-, B-, and A-type sesquioxides structure sequence observed in the room-temperature compression does not coincide with the high-pressure phase sequence of yttrium sesquioxides at high temperature. A reconstructive-type transformation taking place at high temperature yields the Gd2S3 structure around 8 GPa with a drastic change in cation-oxygen coordinations. Ab initio structural optimization suggests that a displacive-type transformation from B- to A-type sesquioxides structure metastably occurs under pressure at room temperature. The calculated density of states indicates that the transition to the Gd2S3 structure causes a significant decrease in the band gap. The Gd2S3 phase was also found to be partially recovered at ambient pressure. We briefly discuss the quenchability of the Gd2S3 structure in sesquioxides on the basis of the enthalpy differences between the ambient phase and the recovered products.

DOI： 10.1021/ic100042z

Web of Science

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Elastic, vibrational and thermodynamic properties of MgGeO3 perovskite (Pv) and postperovskite (PPv) were calculated based on the density functional first principles methods. We found that the calculated properties of MgGeO3 are quite similar to those of MgSiO3 in particular for anomalously large c(66) and small c(55) of PPv, but not fully comparable in particular for the velocity contrasts across the phase change, which are all negative in compressional, shear and bulk velocities at the transition pressure unlike the typical features of the D '' seismic discontinuity. MgGeO3 PPv has larger elastic anisotropy than MgSiO3, but their style is quite similar. Significant orientational preference is needed for PPv polycrystalline aggregate to reproduce seismic shear wave polarization anisotropy observed in D '' except for a case with the c direction aligned vertically. Lattice dynamics calculations indicate that the both phases are vibrationally stable under high pressure, and quasi-harmonic thermodynamics provides the Clapeyron slope of PPv phase boundary of similar to+7.8 MPa/K, which is quite comparable to that reported for MgSiO3. While the calculated Raman frequencies are in excellent agreement with experimental values in Pv, those are found less consistent in PPv.

DOI： 10.1029/2009JB006468

Web of Science

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

Uncertainties in pressure-scales have been one of the most important problems in the high-pressure science and technology. In order to overcome this problem, a method called Scale-Free Unified Analysis (SFUA) was developed to analyze P-V-T equations of state (EOS) of materials available as primary pressure-scales in high-pressure and high-temperature experiments. Here we introduce the concept and analytical procedures of SFUA, and the EOS models determined by applying the method for MgO, Au, and Pt. We will show the great advantages of SFUA to obtain most probable EOS models, and also point out some future prospects to completely dissolve the problem.

DOI： 10.4131/jshpreview.20.210

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1088/1742-6596/215/1/012105

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.81.092104

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2009JB006468

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL ACAD SCIENCES  

The internal structure of the core-mantle boundary (CMB) region of the Earth plays a crucial role in controlling the dynamics and evolution of our planet. We have developed a comprehensive model based on the radial variations of shear velocity in the D '' layer (the base of the lower mantle) and the high-P, T elastic properties of major candidate minerals, including the effects of post-perovskite phase changes. This modeling shows a temperature profile in the lowermost mantle with a CMB temperature of 3,800 +/- 200 K, which suggests that lateral temperature variations of 200-300 K can explain much of the large velocity heterogeneity observed in D ''. A single-crossing phase transition model was found to be more favorable in reproducing the observed seismic wave velocity structure than a double-crossing phase transition model.

DOI： 10.1073/pnas.0905920106

Web of Science

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Equation of state of gold (Au) is revised using the remeasured shock compression data at pressures up to 580 GPa with including the electronic free-energy contribution. The model, even though determined only using pressure-scale-free data, can reproduce not only the shock compression data but also the zero-pressure thermodynamic properties with remarkable accuracy. Previous models for the EOS of copper, silver, and MgO that were constructed using as a basis old shock compression data are found to underestimate the pressure seriously (up to ∼12% at 200 GPa and 300 K). Moreover, we redetermine the EOS model of platinum (Pt) through the same procedure. The determined models of Au and Pt are found mutually highly consistent, which provide quite comparable pressure values in extensive P, T range. These are expected to be more reliable primary pressure standards than previous models. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevB.80.104114

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Equation of state of gold (Au) is revised using the remeasured shock compression data at pressures up to 580 GPa with including the electronic free-energy contribution. The model, even though determined only using pressure-scale-free data, can reproduce not only the shock compression data but also the zero-pressure thermodynamic properties with remarkable accuracy. Previous models for the EOS of copper, silver, and MgO that were constructed using as a basis old shock compression data are found to underestimate the pressure seriously (up to similar to 12% at 200 GPa and 300 K). Moreover, we redetermine the EOS model of platinum (Pt) through the same procedure. The determined models of Au and Pt are found mutually highly consistent, which provide quite comparable pressure values in extensive P, T range. These are expected to be more reliable primary pressure standards than previous models.

DOI： 10.1103/PhysRevB.80.104114

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

In situ X-ray diffraction experiments using a laser-heated diamond anvil cell revealed a novel dense phase with the Gd2S3 structure stabilizing in Sc2O3 at pressures over 19 GPa. Although no phase transformation was induced during room-temperature compression up to 31 GPa, the C rare earth sesquioxide structure transformed into the B rare earth sesquioxicle structure at 10 GPa after laser annealing and subsequently into the Gd2S3 structure at 19 GPa. Neither the A rare earth sesquioxicle structure nor the U2S3 structure was found in Sc2O3. Static density functional lattice energy calculations demonstrated that the C structure prefers Gd2S3 over U2S3 as the post phase. Sc2O3 is the second sesquioxicle, after In2O3, to crystallize into a Gd2S3 structure at high pressures and high temperatures.

DOI： 10.1021/ic9001253

Web of Science

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We investigate the effects of silicon incorporation on the structural stability and elasticity of iron at the Earth's inner core pressures by means of the density functional calculation method in order to clarify the acceptability of silicon to the possible light elements dissolving in the inner core. Calculations show that (1) silicon incorporation enhances the bcc stability field as experimental understandings but hcp phase is the most stable at the inner core pressures even in Fe0.875Si0.125, (2) silicon less affects to the elasticity of bcc iron but decreases shear moduli of hcp and fcc phases, (3) it does not drastically change the elastic wave velocities of iron due to the cancellation of associated changes in density and elastic moduli, (4) both P and S wave velocities for each phase and compound linearly depend on the density. and (5) fcc phase is more elastically anisotropic than hcp phase and the anisotropy is enhanced by silicon. We apply two different high-temperature corrections to the wave velocities. Inner core P-wave velocity is well reproduced in the both models, whereas the calculated S-wave velocities significantly depend on the temperature correction. Small effects of silicon on the density-velocity relations are found in both models. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2009.01.007

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

In order to determine an accurate and reliable high-pressure and high-temperature equation of state (EOS) of MgO, unified analyses were carried out for various pressure-scale-free experimental data sets measured at 1 atm to 196 GPa and 300-3700 K, which are zero-pressure thermal expansion data, zero-pressure and high-temperature adiabatic bulk modulus (K-S) data, room temperature and high-pressure KS data, and shock compression data. After testing several EOS models based on the Mie-Gruneisen-Debye description for the thermal pressures with the Vinet and the third-order Birch-Murnaghan equations for the 300-K isothermal compression, we determined the K'(T0) and gamma(V) using a new functional form gamma = gamma(0){1 + a[(V/V-0)(b)-1]} to express the volume dependence of the Gruneisen parameter. Through least squares analyses with prerequisite zero-pressure and room temperature properties of V-0, K-S0, alpha(0), and C-P0, we simultaneously optimized a set of parameters of K'(T0), gamma(0), alpha, and b required to represent the P-V-T EOS. Determined new EOS models of MgO successfully reproduced all the analyzed P-V-T-K-S data up to 196 GPa and 3700 K within the uncertainties, and the total residuals between calculated and observed pressures were found to be 0.8 GPa in root mean squares. These EOS models, even though very simple, are able to reproduce available data quite accurately in the wide pressure-temperature range and completely independent from other pressure scales. We propose these models for primary pressure calibration standards applicable to quantitative high-pressure and high-temperature experiments.

DOI： 10.1029/2008JB005813

Web of Science

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.pepi.2009.01.008

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2008JB005841

Scopus

researchmap

DOI： 10.1029/2008JB005813

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.gr.2009.05.012

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Electronic spin-pairing transitions of iron and associated effects on the physical properties of host phases have been reported in lower-mantle minerals including ferropericlase, silicate perovskite, and possibly in post-perovskite at lower-mantle pressures. Here we evaluate current understanding of the spin and valence states of iron in the lower-mantle phases, emphasizing the effects of the spin transitions on the density, sound velocities, chemical behavior, and transport properties of the lower-mantle phases. The spin transition of iron in ferropericlase occurs at approximately 50 GPa and room temperature but turns into a wide spin crossover under lower-mantle temperatures. Current experimental results indicate a continuous nature of the spin crossover in silicate perovskite at high pressures, but Which valence state of iron undergoes the spin crossover and what is its associated crystallographic site remain uncertain. The spin transition of iron results in enhanced density, incompressibility, and sound velocities, and reduced radiative thermal conductivity and electrical conductivity in the low-spin ferropericlase, which should be considered in future geophysical and geodynamic modeling of the Earth's lower mantle. In addition, a reduction in sound velocities within the spin transition is recently reported. Our evaluation of the experimental and theoretical pressure-volume results shows that the spin crossover of iron results in a density increase of 2-4% in ferropericlase containing 17-20% FeO. Here we have modeled the density and bulk modulus profiles of ferropericlase across the spin crossover under lower-mantle pressure-temperature conditions and shown how the ratio of the spin states of iron affects our understanding of the state of the Earth's lower mantle. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2008.01.005

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

High-pressure transitions of Ga2 O3 and In2 O3 were examined by using a laser-heated diamond-anvil cell combined with in situ x-ray diffractometry at pressures up to 108 GPa and 20 GPa, respectively. To predict the transition pressure to high-pressure phases, first principles static lattice energy calculations based on the density functional theory were also performed. Rh2 O3 (II) phases were confirmed as post corundum phases for both Ga2 O3 and In2 O3 at about 37 GPa and 7 GPa, respectively. The transition pressures determined by high-pressure experiments are almost consistent with those by theoretical computations. In regard to the present sesquioxides, a link of transition from corundum to perovskite was not confirmed. The Rh2 O3 (II) phases converted to corundum phases under decompression at room temperature. The bulk modulus of Rh2 O3 (II) phase in Ga2 O3 and In2 O3 were determined as 271±10 GPa and 169±4 GPa with their pressure derivatives fixed at 4, respectively. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevB.77.064107

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

High-pressure transitions of Ga2O3 and In2O3 were examined by using a laser-heated diamond-anvil cell combined with in situ x-ray diffractometry at pressures up to 108 GPa and 20 GPa, respectively. To predict the transition pressure to high-pressure phases, first principles static lattice energy calculations based on the density functional theory were also performed. Rh2O3(II) phases were confirmed as post corundum phases for both Ga2O3 and In2O3 at about 37 GPa and 7 GPa, respectively. The transition pressures determined by high-pressure experiments are almost consistent with those by theoretical computations. In regard to the present sesquioxides, a link of transition from corundum to perovskite was not confirmed. The Rh2O3(II) phases converted to corundum phases under decompression at room temperature. The bulk modulus of Rh2O3(II) phase in Ga2O3 and In2O3 were determined as 271 +/- 10 GPa and 169 +/- 4 GPa with their pressure derivatives fixed at 4, respectively.

DOI： 10.1103/PhysRevB.77.064107

Web of Science

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.78.092107

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.pepi.2008.05.015

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.2465/jmps.071022e

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.2138/am.2008.2627

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1073/pnas.0805660105

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

We have investigated the dissociation of iron free ringwoodite, Mg2SiO4 gamma-spinel, into MgO periclase and MgSiO3 perovskite using quasi-harmonic free energy computations within the local density approximation (LDA) and generalized gradient approximation (GGA). The transition pressure, P-tr, obtained from GGA is higher and in much better agreement with experimental measurements than its LDA counterpart. This can be rationalized by close inspection of GGA and LDA functional forms. The Clapeyron slope obtained from this calculation is - 2.9 - - 2.6 MPa/K. Surprisingly, we find a small decrease in bulk sound velocity across this transition. Our results are consistent with 64 +/- 12% ringwoodite volume fraction at the bottom of the transition zone.

DOI： 10.1029/2007GL029462

Web of Science

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Geophysical Monograph Series  

DOI： 10.1029/174GM08

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Superplumes: Beyond Plate Tectonics  

A high-pressure phase transition in iron free MgSiO3 perovskite, the most abundant Earth forming mineral phase, was discovered and reported in 2003-2004. Here, we summarize our theoretical and computational studies on this phase transition and on the physical properties of the newly found post-perovskite phase. The theoretical approach is based on density functional theory and on the plane-wave pseudopotential method. We focus here on the structural, elastic, vibrational, and thermodynamic properties of the post-perovskite phase. The predicted Clapeyron slope of this transition and several elastic properties of the highpressure phase strongly suggest that this new phase is an important candidate for a primary constituent in D″. © 2007 Springer.

DOI： 10.1007/978-1-4020-5750-2_4

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.76.144119

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.76.174108

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.76.092105

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

Iron in the major lower mantle (LM) minerals undergoes a high spin (HS) to low spin (LS) transition at relevant pressures (23-135 GPa). Previous failures of standard first principles approaches to describe this phenomenon have hindered its investigation and the clarification of important consequences. Using a rotationally invariant formulation of LDA+U we report a successful study of this transition in low solute concentration magnesiowustite, (Mg1-xFex)O, (x &lt; 0.2), the second most abundant LM phase. We show that the HS-LS transition goes through an insulating (semiconducting) intermediate mixed spins (MS) state without discontinuous changes in properties, as seen experimentally. We show that the HS state crosses over smoothly to the LS state passing through an insulating MS state where properties change continuously, as seen experimentally.

DOI： 10.1103/PhysRevLett.96.198501

Web of Science

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.2138/am.2006.2221

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssb.200666814

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2006GL025706

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1073/pnas.0506879103

Scopus

researchmap

Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Web of Science

researchmap

Publisher：Japan Association of Mineralogical Sciences  

Mg-Fe substitution is most commonly seen in natural solid solution minerals. High resolution X-ray spectroscopy has recently demonstrated that the major lower mantle (LM) minerals undergo a high-to-low spin transition at LM pressures (23-135 GPa). Previous failures of standard DFT and "LDA+U" approaches to describe this phenomenon have hindered its investigation and consequences of fundamental importance to geophysics, such as heat transport in Earth's mantle. Here, using the latest rotationally invariant first principles formulation of LDA+U with optimized effective U, we report the first successful study of this transition in low solute concentration (Mg(1-x)Fex)O, magnesiumwustite. This is believed to be the second most abundant phase of Earth's LM. This encouraging result appears to open for exploration a new class of problems of enormous significance to deep Earth geophysics

DOI： 10.14824/kobutsu.2005.0.1.0

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2005EO010001

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.2138/am.2005.1628

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2004JB003409

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.72.020103

Scopus

researchmap

Publisher：Japan Association of Mineralogical Sciences  

Hydrogen has large influence on physical and chemical properties of Earth's constituent minerals such as melting temperature and rheological properties. In order to determine the solubility of water in mantle minerals and estimate how much water is stored in Earth's interior, it is critical to investigate the forms of hydrogen in these minerals under high pressure at the atomistic level. We have investigated structural and vibrational properties of hypothetical fully hydrated wadsleyite (Mg7Si4O14(OH)2) using first principles techniques. Cell parameters and linear compressibilities are good agreement with experiments except a axis. We obtained bulk modulus about 138 GPa (K' = 4.5). Using first principles perturbation theory, we have calculated vibrational properties of hydrous wadsleyite. The O-H stretching vibrational frequencies are 3474, 3483, 3503 and 3505 cm-1.

DOI： 10.14824/kobutsu.2005.0.6.0

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

The structural and dynamic properties of water between brucite (0001), talc (001), and halite (100) surfaces have been calculated by classical molecular dynamics (MD) simulations at ambient conditions. The interaction potential models between water and the minerals have been developed by the energy curves obtained from the ab initio electronic state calculations. Orientational anisotropy of water molecules is almost limited in the vicinity of all the surfaces. The significant different properties of water between the surfaces are observed in the density profiles and self-diffusion coefficients. The density profile of water between talc surfaces is flat and the density is equivalent to the bulk one, while those of water between brucite and halite surfaces strongly oscillate with the distance from the surfaces. The self-diffusion coefficients parallel to the surfaces are enhanced in the vicinity of brucite and talc surfaces, and reduced on halite surface compared with that in bulk.

DOI： 10.1080/08927020412331299350

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

A two-phase molecular dynamics simulation of coexisting solid and liquid has been carried out to investigate the melting point of wurtzite-type GaN crystals. The melting point is determined by examining the movement of the interface between the solid and liquid during the simulation. The potential is a two-body interatomic one composed of the long-range Coulomb interaction, the Gilbert-type short-range repulsion, the covalent bonding and covalent repulsion of the modified Morse type, and the van der Waals interaction. The melting point and the interface morphology depend on the crystallization direction. The melting point T-m (K) increases with pressure P (GPa), but there appears a discontinuity in the vicinity of 8-9 GPa. This is due to the solid-electrolyte-like behavior of Ga atoms with a partial charge in the high-pressure region. The discontinuity has not yet been confirmed by experiment. The least-squares fitted result is T-m=2538+177P-4.62P(2) at pressures lower than 8 GPa and T-m=2825+210P-5P(2) at pressures higher than 9 GPa. The Clausius-Clapeyron relation is confirmed using calculated thermodynamic data. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1772878

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Microscopic dislocation structures in wurtzite-type GaN crystal have been studied by the use of molecular dynamics simulation. Parameters for a two-body interatomic potential are determined by the Hartree-Fock ab initio method. A dislocation is generated by the coalescence of the facing planes of a semi-infinite trench structure in the crystal. Six types of trench structures with different depth-directions and extension-directions are examined. Temperatures of 1000 and 1500 K are considered. A core structure with an eightfold ring has been confirmed for edge dislocations along the c axis, though there appear a few atoms that are shifted from the ring core structure. The ring core structure is consistent with reported theoretical expectations and experimental observations. A tenfold ring core structure is also observed for edge dislocations along the c axis. A screw dislocation is generated by an attracting force between gallium and nitrogen atoms across the trench space when the attracting force has a large component parallel to the trench extension direction. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1772879

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We investigated the phase transitions of FeO at high pressure and high temperature up to 87 GPa and 1730 K by in situ synchrotron X-ray diffraction measurements in a laser-heated diamond anvil cell (DAC). The results demonstrated that the NaCl-type (B1) structure of FeO undergoes transition to the NiAs-type (B8) structure above 70 GPa at 1600 K. The density increase across this transition is about 2%. Present B1-B8 transition pressure is consistent with the previous shock-induced transition pressure. The relative intensities of diffraction peaks of the B8 phase may suggest a polytype normal/inverse NiAs structure, which has a metallic nature that could promote the oxygen incorporation into the iron-rich core. Transition to the metallic B8 phase above 70 GPa is also consistent with the earlier electrical resistance measurements. The hexagonal close-packed (hcp) epsilon-phase of Fe coexisted with FeO both at room temperature and high temperatures above 44-87 GPa. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2003.06.011

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

The behaviors of Ga and N vacancies (Schottky defects, Frenkel defects), lattice-site and interstitial Mg atoms, and interstitial H atoms are studied in the wurtzite-type GaN crystal by molecular dynamic simulation. Parameters for a two-body interatomic potential are determined by the Hartree-Fock ab initio method. When there are Schottky defects, Ga and N vacancies are often paired, and the paired vacancies repeatedly form and disappear during the simulation. When there are Frenkel defects, interstitial Ga or N atoms become lattice-site ones by the substitutional-interstitial mechanism. The lattice-site Mg atom shows a very stable state, stays there for a long period and undergoes thermal vibration. The interstitial Mg atom is in a semistable state at the cage center of a hexagonal crystal structure. The Mg atom undergoes thermal vibration there, then hops from one cage center to an adjacent one. The diffusivity of interstitial Mg atoms on the (0001) plane is predominant compared with the diffusivity along the [0001] direction.

DOI： 10.1143/JJAP.43.522

Web of Science

researchmap

Language：Japanese   Publisher：The Japan Society of High Pressure Science and Technology  

An essential and fundamental problem to determine a <i>P-V-T</i> thermal equation of state (EOS) of solid as a primary pressure standard is the fact that the pressure or volume dependence of thermal property of solid, that is necessary for the conversion of Hugoniot to isotherm, cannot be obtained experimentally. In this article, theory of <i>P-V-T</i> EOS of solid is reviewed first, and based on our recent <i>ab initio</i> results of gold, validity of previous <i>P-V-T</i> EOS models and especially volume dependence of Grüneisen parameter are discussed in detail.

DOI： 10.4131/jshpreview.14.61

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00236572395?from=CiNii

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2004GL020278

Scopus

researchmap

Language：Japanese   Publisher：The Japan Society of High Pressure Science and Technology  

Theoretical study of mineral physics has rapidly progressed by first principles method based on the density functional theory. In this article, recent studies of the Earth's constituents and related materials by means of the first principles electronic structure calculation methods are reviewed. Especially, calculations of high-pressure thermodynamic properties, PVT equations of state, high-pressure elasticity, high-PT phase stability are reported. These techniques are applied to study thermochemical state and physical properties of the Earth's lower mantle.

DOI： 10.4131/jshpreview.14.173

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00241746156?from=CiNii

Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2004GL019649

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.epsl.2004.05.017

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：INT UNION CRYSTALLOGRAPHY  

Recently, there has been substantial interest in the new high-pressure polymorphs of GeO2 synthesized in the laboratory. Previous investigators reported the synthesis of 'CaCl2-type', 'alpha-PbO2-type' and 'pyrite-type (modfied-fluorite-type)' GeO2 at pressures of 30 - 130 GPa in laser-heated diamond anvil cells. In order to provide definitive information about the new high-pressure polymorphs, we performed Rietveld refinements of the structures. The structure refinements confirm that two of these high-pressure phases do have the alpha-PbO2-type and pyrite-type (modified-fluorite-type) structures.

DOI： 10.1107/S0108768103021761

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Observations of the phase transition between the CaCl2-type (Pnnm) and alpha-PbO2-type (Pbcn) structures of germanium dioxide (GeO2) were carried out using quench and in situ x-ray diffraction methods in a laser-heated diamond anvil cell (LHDAC). First-principle theoretical simulations were also performed to complement the experimental results. The experiments showed that the transition had a positive dP/dT dependence. The phase boundary between the CaCl2-type and alpha-PbO2-type structures in the temperature range 1500-2400 K was determined to be P (GPa)=(53+/-3)+(0.011+/-0.005)(T-1800) (K) based on the equation of state of platinum and the ruby scale. The positive slope of the transition is consistent with the known phase boundary between the CaCl2-type and alpha-PbO2-type structures of tin dioxide (SnO2) as germanium dioxide analog and theoretical simulation results. However, our results do not agree with the slope of the phase boundary of silica (SiO2), which has been reported to have a negative slope.

DOI： 10.1103/PhysRevB.68.134108

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

[1] The P-V-T equation of state (EOS) of gold is the most frequently used pressure calibration standard in high-P-T in situ experiments. Empirically proposed EOS models, however, severely scatter under high-P-T conditions, which is a serious problem for studies of the deep Earth. In this study, the EOS of gold is predicted using a first-principles electronic structure calculation method without any empirical parameters. The calculated thermoelastic properties of gold compare favorably to experimental data at ambient conditions so that B-T0 and B'(T0) are 166.7 GPa and 6.12, respectively. Up to V/V-a = 0.7, the calculated Gruneisen parameter of gold depends on volume according to the function gamma/gamma(a) = (V/V-a)(zeta) with gamma(a) of 3.16 and zeta of 2.15. On the basis of these data, the validity of previous EOS models is discussed. It is found that the present ab initio EOS provides a 1.3 GPa higher pressure than Anderson's scale at 23 GPa and 1800 K and largely reduces the discrepancy observed between conditions at the transition of Mg2SiO4 and the 660-km seismic discontinuity. However, a discrepancy of about 0.7 GPa still remains between the 660-km discontinuity and the postspinel transition.

DOI： 10.1029/2003JB002446

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Structural phase transitions of germanium dioxide (GeO2) have been investigated at pressures up to 120 GPa, which was heated to a temperature above 2000 K, using a laser-heated diamond anvil cell technique. A phase transition between CaCl2-type and alpha-PbO2-type phases was observed at about 50 GPa. At pressures higher than 90 GPa, we also observed the occurrence of a new high-pressure phase of pyrite-type (modified-fluorite type) structure (Pa (3) over bar) that is denser than other known GeO2 phases. Our results were consistent with the high-pressure transition sequence of tin dioxide (SnO2) as analog of GeO2. The new structure of the GeO2 high-pressure phase may be that of high-pressure silica (SiO2) phase predicted by the theoretical investigations.

DOI： 10.1103/PhysRevE.68.014103

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WILEY-VCH, INC  

A two-phase molecular dynamic simulation of coexisting solid and liquid has been made for a wurtzite-type GaN crystal. The melting point is determined by examining the movement of the interface between solid and liquid during the calculation. The pressure dependence of the melting point is systematically obtained for the first time. The melting point To, increases linearly with pressure P as T-m(K) = 2513 + 186 x P(GPa). (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.200303476

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Observations of the phase transition between the CaCl2-type (Pnnm) and α-PbO2-type (Pbcn) structures of germanium dioxide (GeO2) were carried out using quench and in situ x-ray diffraction methods in a laser-heated diamond anvil cell (LHDAC). First-principle theoretical simulations were also performed to complement the experimental results. The experiments showed that the transition had a positive dP/dT dependence. The phase boundary between the CaCl2-type and α-PbO2-type structures in the temperature range 1500–2400 K was determined to be P (GPa)=(53±3)+(0.011±0.005)(T-1800) (K) based on the equation of state of platinum and the ruby scale. The positive slope of the transition is consistent with the known phase boundary between the CaCl2-type and α-PbO2-type structures of tin dioxide (SnO2) as germanium dioxide analog and theoretical simulation results. However, our results do not agree with the slope of the phase boundary of silica (SiO2), which has been reported to have a negative slope. © 2003 The American Physical Society.

DOI： 10.1103/PhysRevB.68.134108

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

The behaviors of Ga and N vacancies (Schottky defects, Frenkel defects), lattice-site and interstitial Mg atoms, and interstitial H atoms have been studied in the wurtzite-type GaN crystal by molecular dynamic simulation. The diffusivity of interstitial Mg atoms on the (0001) plane is predominant compared with the diffusivity along the [0001] direction. Diffusion coefficients of interstitial Mg atoms are composed of two Arrhenius formula for temperatures from 850 K to 2000 K. The one reflects the high-possibility occurrence of jumping movements among cage centers of hexagonal crystal structure for higher temperature. The other reflects the thermal vibration at the cage center for lower temperature. © 2003 WILEY-VCH Verlag GmbH &amp
Co. KGaA.

DOI： 10.1002/pssc.200303298

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WILEY-VCH, INC  

The behaviors of Ga and N vacancies (Schottky defects, Frenkel defects), lattice-site and interstitial Mg atoms, and interstitial H atoms have been studied in the wurtzite-type GaN crystal by molecular dynamic simulation. The diffusivity of interstitial Mg atoms on the (0001) plane is predominant compared with the diffusivity along the [0001] direction. Diffusion coefficients of interstitial Mg atoms are composed of two Arrhenius formula for temperatures from 850 K to 2000 K. The one reflects the high-possibility occurrence of jumping movements among cage centers of hexagonal crystal structure for higher temperature. The other reflects the thermal vibration at the cage center for lower temperature. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.200303298

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Structural phase transitions of germanium dioxide (GeO2) have been investigated at pressures up to 120 GPa, which was heated to a temperature above 2000 K, using a laser-heated diamond anvil cell technique. A phase transition between CaCl2-type and α-PbO2-type phases was observed at about 50 GPa. At pressures higher than 90 GPa, we also observed the occurrence of a new high-pressure phase of pyrite-type (modified-fluorite type) structure (Pa3−) that is denser than other known GeO2 phases. Our results were consistent with the high-pressure transition sequence of tin dioxide (SnO2) as analog of GeO2. The new structure of the GeO2 high-pressure phase may be that of high-pressure silica (SiO2) phase predicted by the theoretical investigations. © 2003 The American Physical Society.

DOI： 10.1103/PhysRevB.68.014103

Scopus

researchmap

researchmap

researchmap

researchmap

DOI： 10.1016/S0039-6028(03)00577-6

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

A two-phase molecular dynamic simulation of coexisting solid and liquid has been made for a wurtzite-type GaN crystal. The melting point is determined by examining the movement of the interface between solid and liquid during the calculation. The pressure dependence of the melting point is systematically obtained for the first time. The melting point Tm increases linearly with pressure P as Tm(K) = 2513 + 186 × P(GPa). © 2003 WILEY-VCH Verlag GmbH &amp
Co. KGaA.

DOI： 10.1002/pssc.200303476

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Electronic thermal pressures (ETP's) of metal Au and Pt are predicted by first-principles electronic structure calculations based on the density functional theory in order to refine their thermal equations of state (EOS) which are frequently used as pressure scales in in situ high-pressure and high-temperature experiment. We find a large difference in the magnitude of ETP's for Au and Pt, which can be attributed to the different positions of the Fermi level. The ETP for Au is considerably smaller than it for Pt. The latter reaches 0.85 GPa at 2000 K, whereas the former is only 0.05 GPa at the same temperature. We also find a different temperature dependence of the ETP's of Au and Pt under high temperature, which arises from the different manner of thermal excitation. It is illustrated that the corrections of the ETP for known EOS of Au and Pt becomes substantially important with increasing temperature, and the ETP can perfectly compensate for the measured discrepancy of pressure values determined by previous EOS of Au and Pt.

DOI： 10.1103/PhysRevB.66.094115

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Elastic properties and their pressure dependence of rare gas solids (RGSs) Ne, Ar, Kr, and Xe are calculated using the ab initio full-potential linear muffin-tin-orbital method to study their systematics. Though the local density approximation (LDA) underestimates volume of these substances, especially Ne, equations of state and elastic constants are well reproduced in the entire pressure range up to a megabar. The Cauchy deviation, the Zener anisotropy ratio, and the normalized elastic constant are investigated as a function of pressure. It is found that many-body contribution to the interatomic force surprisingly increases with increasing pressure even in all RGSs and it is larger in the heavier element. The elastic anisotropy of all four RGSs gradually decreases with increasing pressure. The normalized elastic constants c(11)' and c(12)' largely deviate from the ideal values, and c(ij)''s are remarkably insensitive to pressure over 10 GPa. Moreover, no elastic instability appears under high pressure in all RGSs. Consequently, LDA is sufficiently valid even for RGS since the van der Waals interaction becomes minor with increasing pressure. These trends of high-pressure elastic property are quite different from those of ionic solid and metal. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1502241

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Electronic thermal pressures (ETP's) of metal Au and Pt are predicted by first-principles electronic structure calculations based on the density functional theory in order to refine their thermal equations of state (EOS) which are frequently used as pressure scales in in situ high-pressure and high-temperature experiment. We find a large difference in the magnitude of ETP's for Au and Pt, which can be attributed to the different positions of the Fermi level. The ETP for Au is considerably smaller than it for Pt. The latter reaches 0.85 GPa at 2000 K, whereas the former is only 0.05 GPa at the same temperature. We also find a different temperature dependence of the ETP's of Au and Pt under high temperature, which arises from the different manner of thermal excitation. It is illustrated that the corrections of the ETP for known EOS of Au and Pt becomes substantially important with increasing temperature, and the ETP can perfectly compensate for the measured discrepancy of pressure values determined by previous EOS of Au and Pt.

DOI： 10.1103/PhysRevB.66.094115

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Pressure dependence of elastic properties of crystalline Au is calculated based on the first-principles method within the local density approximation for the first time. The calculated equation of state agrees quite well with the results of previous high-pressure experiments. From the present study we find several unique features of the elasticity of Au as follows. (1) The calculated dependence of elastic constants on pressure supports the experiments demonstrating relatively smaller pressure derivatives. (2) The small tetragonal shear constant c(s)=(c(11)-c(12))/2 in Au is remarkably insensitive to pressure, but elastic instability does not appear in the calculated pressure range. This feature is inferred to result from a small covalent nature in the chemical bonding in Au. (3) The elastic anisotropy increases with pressure. The normalized elastic constants considerably deviate from the ideal values and keep almost constant in wide volume variations. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1429643

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Electronic thermal pressures (ETP’s) of metal Au and Pt are predicted by first-principles electronic structure calculations based on the density functional theory in order to refine their thermal equations of state (EOS) which are frequently used as pressure scales in in situ high-pressure and high-temperature experiment. We find a large difference in the magnitude of ETP’s for Au and Pt, which can be attributed to the different positions of the Fermi level. The ETP for Au is considerably smaller than it for Pt. The latter reaches 0.85 GPa at 2000 K, whereas the former is only 0.05 GPa at the same temperature. We also find a different temperature dependence of the ETP’s of Au and Pt under high temperature, which arises from the different manner of thermal excitation. It is illustrated that the corrections of the ETP for known EOS of Au and Pt becomes substantially important with increasing temperature, and the ETP can perfectly compensate for the measured discrepancy of pressure values determined by previous EOS of Au and Pt. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.66.094115

Scopus

researchmap

Language：Japanese   Publisher：The Clay Science Society of Japan  

Molecular dynamics (MD) simulations have been performed to investigate the elastic properties of a single layer of beidellite. NVT or NPT ensemble is selected at 300 K in which N (number of atoms in a basic cell), T (temperature) and V (volume of the basic cell) or P (pressure) are kept constant, respectively. The total freedom of atomic motions was allowed by applying the atom-atom pair interaction model. The size of a single clay layer was reduced gradually along either the a-or b-axis to the final contraction of 0 - 45% in the MD simulations. It has been observed that a single clay layer takes a curved form under such external force. The effect of water molecules existing around a clay layer was investigated under the same conditions.

DOI： 10.11362/jcssjnendokagaku1961.41.190

CiNii Books

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

To determine the bulk modulus (B-0) and its pressure derivative (B'(0)) of wurtzite-type GaN, the room temperature pressure (P)-volume (V) equation-of-state (EOS) is precisely measured up to 16 GPa by quasihydrostatic compression experiments with in situ energy-dispersive X-ray diffraction. In the present experiments we especially pay attention to the hydrostaticity of pressure conditions since previous studies implied that it largely affected to B-0 and B-0'. Nonhydrostatic effect is eliminated by enough annealing at each pressure. We find B-0 = 202.4 GPa and B-0' = 4.5 by fitting to the third-order Birch-Murnaghan EOS. Though being different from the earlier experimental results using diamond-anvil cells, these values are quite concordant with recent data from Brillouin spectroscopies and ab initio calculations. Furthermore, we confirm that linear compressibilities (beta) along a and c directions are almost same in GaN as beta(a) = 1.481 X 10(-3) and beta(c) = 1.402 X 10(-3), differing from other wurtzite-type group III nitrides. This corresponds to a small pressure dependence of the axial ratio c/a and the high ideality of the GaN lattice not only at ambient pressure but also under high pressures. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0038-1098(01)00492-6

Web of Science

researchmap

Publishing type：Research paper (scientific journal)  

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER-VERLAG  

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.

DOI： 10.1007/s002690100174

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The elastic properties and their pressure dependence of four B1-type alkaline earth oxides, MgO, CaO, SrO, and BaO, are calculated using the ab initio full-potential linear muffin-tin-orbital (FP-LMTO) generalized gradient approximated (GGA) method to elucidate their systematics. The calculated results agree quite well with the comparable experimental data. The large pressure dependence of c(11) and c(44) of MgO observed over 25 GPa is not predicted as well as the previous local-density approximation (LDA) calculations. It is inferred that the high-pressure measurement of elastic constant is quite sensitive to nonhydrostaticity. The deviation from the Cauchy relation and the elastic anisotropy are investigated. It is found that the interatomic interaction in SrO is nearest to the two-body force and the many-body contribution is largest in MgO. The elastic anisotropy in SrO and BaO are almost the same and only MgO has a large positive anisotropy under low pressure. The normalized elastic constants c(ij)' are introduced for more detail analysis. It is found that while there is no substantial difference in c(11)' and c(12)' of the four oxides, only c(44)' and its pressure dependence vary systematically. The difference in the Cauchy deviation and elastic anisotropy of alkaline earth oxides under pressure is characterized by c(44). (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1371498

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER VERLAG  

We simulated quartz-type GeO2 and investigated its high-pressure transformation using the molecular dynamics (MD) simulation method with a model potential, The calculated results under hydrostatic compression indicated that a pi pressure-induced amorphization of quartz-type GeO2 originated from the mechanical instability of the quartz lattice as, in previous theoretical studies of SiO2. Furthermore, quartz-type GeO2 directly transformed to a rutile-like structure with only subtle displacements of ions under sigma(xy) imposed shear stressed decompression. This is the first reproduction of the quartz-to-rutile transformation. A possible pathway of this transition is proposed in this study.

DOI： 10.1007/s002690050002

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：R OLDENBOURG VERLAG  

Molecular orbital calculations using descrete-variational Xa method were carried out in order to investigate the bond nature of SiO2, GeO2 and SnO2. The bond overlap populations and the d-orbital populations of cations were decreased with increasing the atomic number. The deformation density maps of electronic charge show the accumulation of electron in interatomic region which is most dominant in SiO2. The calculated density of states indicates that the bond character of SiO2 is more covalent than that of GeO2 and SnO2. From the excited d-electron partial density of states, it is inferred that the Si excited-3d has some connection with the bond nature of SiO2 covalency.

Web of Science

researchmap

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER VERLAG  

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.

DOI： 10.1007/s002690050179

Web of Science

researchmap

Language：Japanese   Publisher：海洋出版  

CiNii Books

researchmap

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER VERLAG  

A two-body interatomic potential model for GeO2 polymorphs has been determined to simulate the structure change of them by semi-empirical procedure, total lattice energy minimization of GeO2 polymorphs. Based on this potential, two polymorphs of GeO2; alpha-quartz-type and rutile-type, have been reproduced using the molecular dynamics (MD) simulation techniques. Crystal structures, bulk moduli, volume thermal expansion coefficients and enthalpies of these polymorphs of Ge0(2) were simulated. In spite of the simple form of the potential, these simulated structural values, bulk moduli and thermal expansivities are in excellent agreement with the reliable experimental data in respect to both polymorphs. Using this potential, MD simulation was further used to study the structural changes of Ge02 under high pressure. We have investigated the pressure-induced amorphization. As reported in previous experimental studies, quartz-type GeO2 undergoes pressure-induced crystalline-to-amorphous transformation at room temperature, the same as other quartz compounds; SiO2, AlPO4. Under hydrostatic compression, in this study, alpha-quartz-type GeO2 transformed to a denser amorphous state at 7.4 GPa with change of the packing of oxygen ions and increase of germanium coordination. At higher pressure still, rutile-type GeO2 transformed to a new phase of CaCl2-type structure as a post-rutile candidate.

DOI： 10.1007/s002690050091

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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.

DOI： 10.1016/S0038-1098(98)00194-X

Web of Science

researchmap

Language：Japanese  

DOI： 10.2465/gkk1952.27.137

CiNii Books

researchmap

Language：Japanese   Publisher：The Crystallographic Society of Japan  

DOI： 10.5940/jcrsj.39.Supplement_129

researchmap

Language：Japanese   Publisher：The Crystallographic Society of Japan  

DOI： 10.5940/jcrsj.39.Supplement_68

researchmap

Publishing type：Research paper (scientific journal)  

The pair potentials of Ge-O bonds in rutile type, α-quartz type and vitreous GeO2 have been investigated by the EXAFS technique from 10 K to 1000 K. An anharmonic effective pair potential for Ge-O bond has been dertermined by the numerical integration of EXAFS fanction with amussing the classical Boltzmann distribution. The radial distributions of Ge-O in α-quartz type obtained from EXAFS and our molecular dynamics (MD) simulation agree well with each other. The pair potential of Ge-O bond is not noticably changed with structural transformation, except for the four coplanar Ge-O bonds in the rutile type structure.

DOI： 10.1051/jp4:19972180

Scopus

researchmap

Language：English   Publisher：R OLDENBOURG VERLAG  

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.

Web of Science

researchmap

Total pages：xiii, 519p   Language：Japanese  

CiNii Books

researchmap

researchmap

researchmap

researchmap

researchmap

researchmap

researchmap

researchmap

researchmap

researchmap

researchmap

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Books

researchmap

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Books

researchmap

J-GLOBAL

researchmap

J-GLOBAL

researchmap

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Books

researchmap

Language：Japanese   Publisher：レーザー学会  

CiNii Books

researchmap

J-GLOBAL

researchmap

Language：English  

CiNii Books

researchmap

Language：English  

CiNii Books

researchmap

Language：English  

CiNii Books

researchmap

J-GLOBAL

researchmap

J-GLOBAL

researchmap

J-GLOBAL

researchmap

DOI： 10.5026/jgeography.119.1197

researchmap

DOI： 10.5940/jcrsj.53.2

researchmap

Language：English   Publisher：AMER GEOPHYSICAL UNION  

DOI： 10.1029/2010JB007959

Web of Science

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：English   Publishing type：Research paper, summary (international conference)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Web of Science

researchmap

Language：English   Publishing type：Research paper, summary (international conference)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Web of Science

researchmap

Language：English   Publishing type：Research paper, summary (international conference)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Web of Science

researchmap

Language：English  

CiNii Books

researchmap

Language：English  

CiNii Books

researchmap

Language：English  

CiNii Books

researchmap

researchmap

Language：Japanese   Publisher：日本粘土学会  

バイデライドの粘土単一層に外力を加えた場合の層の示す力学的応答を分子動力学によってシミュレーションした.その結果,粘土単一層はバネのような弾性特性を示すことが観測できた.粘土単一層の力学的特性を表す指標として弾性係数の算出を試みた.粘土単一層の弾性定数は約14.5GPaと見積もることができ,バルクのマイカの181GPaと比較して小さく,柔軟であることがわかった.

CiNii Books

researchmap

Language：English   Publisher：AMER PHYSICAL SOC  

DOI： 10.1103/PhysRevB.67.019902

Web of Science

researchmap

Language：Japanese  

DOI： 10.11362/cssj2.46.0.114.0

J-GLOBAL

researchmap

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Books

researchmap

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Event date： 2019.5

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：Japanese   Presentation type：Poster presentation  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Oral presentation (keynote)  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：Japanese   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：愛媛大学  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：New Orleans Ernest N. Morial Convention Center, New Orleans, USA  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：New Orleans Ernest N. Morial Convention Center, New Orleans, USA  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：New Orleans Ernest N. Morial Convention Center, New Orleans, USA  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：New Orleans Ernest N. Morial Convention Center, New Orleans, USA  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：幕張メッセ（千葉県千葉市）  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：Melbourne   Country：Australia  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：京都大学（京都府）  

researchmap

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：大阪市立大学(大阪府大阪市）  

researchmap

Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：愛媛大学（愛媛県松山市）  

researchmap

Language：English   Presentation type：Poster presentation  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：English   Presentation type：Poster presentation  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Kobe International Conference Center, Kobe, Japan  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：English   Presentation type：Poster presentation  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：English   Presentation type：Poster presentation  

Venue：Makuhari Messe, Chiba, Japan  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：New Orleans Ernest N. Morial Convention Center, New Orleans, USA  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Saint Malo, France  

researchmap

Language：English   Presentation type：Oral presentation (keynote)  

Venue：Saint Malo, France  

researchmap

Language：English   Presentation type：Oral presentation (general)  

Venue：China National Convention Center,Beijing,China  

researchmap

Language：English   Presentation type：Poster presentation  

Venue：China National Convention Center,Beijing,China  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Poster presentation  

researchmap

Language：Japanese   Presentation type：Poster presentation  

researchmap

Language：English  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap