研究者詳細 - 芳野　極

論文 - 芳野　極

分割表示 162 件中 101 - 120 件目／全件表示 >>

Molecular dynamics simulation and electrical conductivity measurement of Na2O center dot 3SiO(2) melt under high pressure; relationship between its structure and properties 査読

Fumiya Noritake, Katsuyuki Kawamura, Takashi Yoshino, Eiichi Takahashi

JOURNAL OF NON-CRYSTALLINE SOLIDS 358 ( 23 ) 3109 - 3118 2012年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The relationship between structure and properties of the Na2O center dot 3SiO(2) melt was investigated using molecular dynamics (MD) simulations and electrical conductivity measurements under high pressure. The inter-atomic potential was newly developed using energy surfaces derived by quantum chemical calculations. In MD simulations, changes of the structure and properties were observed as a function of pressure. An increase in self-diffusion coefficients of network forming atoms is closely related to the distortion of the -Si-O- network and the changes in distributions of poly-membered rings which forms the -Si-O- network. In the electrical conductivity measurements, we found a negative pressure dependence at least up to 3 GPa. This suggests that electric conductivity in Na2O center dot 3SiO(2) melt is controlled by ionic conduction of sodium atoms. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jnoncrysol.2012.08.027

その他リンク： http://orcid.org/0000-0002-5422-7396

Re-evaluation of electrical conductivity of anhydrous and hydrous wadsleyite (vol 337, pg 56, 2012) 査読

Takashi Yoshino, Tomoo Katsura

EARTH AND PLANETARY SCIENCE LETTERS 357 422 - 422 2012年12月

Electrical conductivity of enstatite as a function of water content: Implications for the electrical structure in the upper mantle 査読

Baohua Zhang, Takashi Yoshino, Xiaoping Wu, Takuya Matsuzaki, Shuangming Shan, Tomoo Katsura

EARTH AND PLANETARY SCIENCE LETTERS 357 11 - 20 2012年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The electrical conductivity of Ca-free aluminous enstatite with various water contents has been determined at a pressure of 3 GPa in a Kawai-type multi-anvil apparatus. Impedance spectroscopy was performed for both hydrogen-doped and -undoped samples in a frequency range from 0.1 Hz to 1 MHz to examine the effect of water on conductivity. Two conduction mechanisms were identified for hydrogen-undoped samples at temperature of 1000-1723 K and for hydrogen-doped samples at relatively lower temperature range of 500-900 K to minimize dehydration of samples. For the hydrogen-undoped samples, the activation enthalpy is around 1.9 eV at the higher temperatures range ( > 1300 K) suggesting that the dominant charge transfer mechanism is Fe2+ -Fe3+ hopping (small polaron) conduction. For the hydrogen-doped samples measured below 900 K, the activation enthalpy decreases from 1.11 to 0.70 eV, and the conductivity values systematically increase with increasing water content, suggesting that proton conduction is the dominant conduction mechanism. Taking hopping conduction and water content dependence of activation enthalpy for proton conduction into account, all electrical conductivity data were fitted to the formula o-=o-ohexp( HhIkT)+ sigma(op)C(w)exp[-(H-p(o)-alpha C-w(1/3))/kT], where sigma(0) is pre-exponential factor, C-w is the water content in weight percent, H is the activation enthalpy. H-p(o), is the activation enthalpy for proton conduction at very low water concentration, alpha is the geometrical factor, k is the Boltzmann constant, T is absolution temperature and subscripts h and p represent hopping and proton conductions, respectively. Using the present results, a laboratory-based conductivity-depth profile in the Earth's upper mantle has been constructed as a function of water content. Comparison of our model with the currently available geophysical observations beneath the Eastern Pacific Rise indicates that hydrous aluminous enstatite cannot account for the high conductivity anomaly at the top of the asthenosphere as well as hydrous olivine. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2012.09.020

その他リンク： http://orcid.org/0000-0002-5422-7396

Electrical conductivity of magnetite-bearing serpentinite during shear deformation 査読

Seiya Kawano, Takashi Yoshino, Ikuo Katayama

GEOPHYSICAL RESEARCH LETTERS 39 ( 20 ) 2012年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Electrical conductivity of serpentinite with various amounts of magnetite was measured during shear deformation at high pressure and temperatures (P = 1.0 GPa, T = 750 K) corresponding to mantle wedge conditions to evaluate the contribution of aligned magnetite to the bulk conductivity of serpentinite. Under hydrostatic conditions, the sample conductivity considerably increases when the magnetite volume fraction exceeds 25% in volume, suggesting the presence of the percolation threshold for magnetite interconnection. During shear deformation, the conductivity for the samples with less than 25 vol.% magnetite increased by an order of magnitude or higher with increasing shear strain up to 9, which is likely a result of the clustering or realignment of magnetite grains in the serpentinites. However, activation enthalpy was nearly constant before and after deformation experiments, suggesting that shear deformation is unlikely to enhance establishment of interconnection of magnetite. Consequently, more than 25 vol.% magnetite is needed to establish connectivity of magnetite in serpentinite. On the other hand, the conductivity of serpentinite with low volume fraction of magnetite (5%), which is typical concentration of natural serpentinites, is almost similar to that of magnetite-free serpentinites. The present results show that the interconnection of magnetite in serpentinites by shear deformation is not expected as an origin of the high conductivity anomaly occasionally observed at the slab interface in the mantle wedge. The origin of high conductivity, therefore, indicates the presence of aqueous fluid with high salinity rather than the magnetite interconnection. Citation: Kawano, S., T. Yoshino, and I. Katayama (2012), Electrical conductivity of magnetite-bearing serpentinite during shear deformation, Geophys. Res. Lett., 39, L20313, doi:10.1029/2012GL053652.

DOI： 10.1029/2012GL053652

その他リンク： http://orcid.org/0000-0002-5422-7396

P-V-T equation of state for epsilon-iron up to 80 GPa and 1900 K using the Kawai-type high pressure apparatus equipped with sintered diamond anvils 査読

Daisuke Yamazaki, Eiji Ito, Takashi Yoshino, Akira Yoneda, Xinzhuan Guo, Baohua Zhang, Wei Sun, Akira Shimojuku, Noriyoshi Tsujino, Takehiro Kunimoto, Yuji Higo, Ken-ichi Funakoshi

GEOPHYSICAL RESEARCH LETTERS 39 ( 20 ) 2012年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

In order to determine the P-V-T equation of state of epsilon-iron, in situ X-ray observations were carried out at pressures up to 80 GPa and temperatures up to 1900 K using the Kawai-type high pressure apparatus equipped with sintered diamond anvils which was interfaced with synchrotron radiation. The present results indicate the unit cell volume at ambient conditions V-0 = 22.15(5) angstrom(3), the isothermal bulk modulus K-T0 = 202(7) GPa and its pressure derivative K-T0' = 4.5(2), the Debye temperature theta(0) = 1173(62) K, Gruneisen parameter at ambient pressure gamma(0) = 3.2(2), and its logarithmic volume dependence q = 0.8(3). Furthermore, thermal expansion coefficient at ambient pressure was determined to be alpha(0)(K-1) = 3.7(2) x 10(-5) + 7.2(6) x 10(-8)(T-300) and Anderson-Gruneisen parameter delta(T) = 6.2(3). Using these parameters, we have estimated the density of epsilon-iron at the inner core conditions to be similar to 3% denser than the value inferred from seismological observation. This result indicates that certain amount of light elements should be contained in the inner core as well as in the outer core but in definitely smaller amount. Citation: Yamazaki, D., et al. (2012), P-V-T equation of state for epsilon-iron up to 80 GPa and 1900 K using the Kawai-type high pressure apparatus equipped with sintered diamond anvils, Geophys. Res. Lett., 39, L20308, doi: 10.1029/2012GL053540.

DOI： 10.1029/2012GL053540

その他リンク： http://orcid.org/0000-0002-5422-7396

Effect of temperature, pressure and iron content on the electrical conductivity of olivine and its high-pressure polymorphs 査読

Takashi Yoshino, Akira Shimojuku, Shuanming Shan, Xinzhuan Guo, Daisuke Yamazaki, Eiji Ito, Yuji Higo, Ken-ichi Funakoshi

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 117 ( 8 ) 2012年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

The electrical conductivity of olivine and its high-pressure polymorphs with various iron contents [X-Fe = Fe/(Fe + Mg) = 0.1, 0.2, 0.3, 0.5, 0.7 and 1.0] was measured over a wide range of pressure (P) and temperature (T) conditions covering the stability field of olivine, wadsleyite and ringwoodite in a Kawai-type multianvil apparatus. The pressure was determined using in situ X-ray diffraction of MgO as a pressure marker in SPring 8. Molybdenum electrodes were used so that oxygen fugacity is similar to that for the iron-wustite buffer. The transition from low-pressure phase to high-pressure phase led to an increase of conductivity. In the stability field of each phase, the electrical conductivity slightly increased with increasing pressure at a constant temperature, suggesting a negative activation volume. The conductivity increased with increasing total iron content for each phase. All electrical conductivity data fit the formula for electrical conductivity sigma = sigma(0) X(Fe)exp{-[Delta E-0 - alpha X-Fe(1/3) + P(Delta V-0 - beta X-Fe)]/kT}, where sigma(0) is the pre-exponential term, Delta E-0 and Delta V-0 are the activation energy and the activation volume at very low total iron concentration, respectively, and k is the Boltzmann constant. The activation energy decreased with increasing total Fe content in olivine and ringwoodite. Dependence of the activation energy on the total Fe content suggests that the dominant mechanism of charge transport is Fe2+-Fe3+ hopping (small polaron). The activation volume for small polaron conduction in olivine and its high-pressure polymorphs tends to decrease with total Fe content. For olivine with low Fe content, the activation volume for small polaron conduction still is negative and very small. Assuming constant Fe content (X-Fe = 0.1) and oxygen buffer condition, the conductivity will increase with depth mainly due to the increase of the temperature along the mantle adiabat.

DOI： 10.1029/2011JB008774

その他リンク： http://orcid.org/0000-0002-5422-7396

Re-evaluation of electrical conductivity of anhydrous and hydrous wadsleyite 査読

Takashi Yoshino, Tomoo Katsura

EARTH AND PLANETARY SCIENCE LETTERS 337 56 - 67 2012年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Recent laboratory electrical conductivity measurements of the main mantle constituent minerals have represented considerable efforts to determine the effects of water content on electrical conductivity. However, there are large discrepancies between the results of Yoshino et al. (2008a) and those of Dai and Karato (2009a) on hopping conduction and the effects of water on the electrical conductivity of wadsleyite. To investigate the cause of these discrepancies, the electrical conductivity of anhydrous and hydrous wadsleyite were newly measured under low and high temperature conditions by impedance spectroscopy. The conductivity values of dry wadsleyite aggregates with less than 2 ppm H2O by weight were similar to those for hopping conduction reported by Yoshino et al. (2008a) and distinctly higher than those of Dai and Karat (2009a). For hydrous wadsleyite, at temperatures below 1000 K, the electrical conductivity in an Arrhenius plot was repeatable along the heating-cooling paths and was similar to the results of Yoshino et al. (2008a). The impedance spectrum in the complex impedance plane of hydrous wadsleyite showed a semicircular shape, and the infrared spectrum did not show any shape change after the conductivity measurements. In contrast, when the temperature exceeds 1000 K, the electrical conductivity in an Arrhenius plot showed higher activation enthalpy. The impedance spectra were greatly distorted and the impedance arc contained at least two relaxation processes. This shape is similar to those reported by Dai and Karato (2009a) who measured the conductivity above 1000 K. The infrared spectra showed a large contribution from molecular water after conductivity measurements, suggesting significant dehydration during the conductivity measurements. In summary, the results obtained from conductivity measurements at higher temperatures ( > 1000 K) do not represent the proton conduction in the grain interior. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2012.05.023

その他リンク： http://orcid.org/0000-0002-5422-7396

Electrical conductivity of fluid-bearing quartzite under lower crustal conditions 査読

Akira Shimojuku, Takashi Yoshino, Daisuke Yamazaki, Takamoto Okudaira

PHYSICS OF THE EARTH AND PLANETARY INTERIORS 198 1 - 8 2012年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The electrical conductivity of fluid-bearing quartzite was determined as function of temperature and fluid fraction at 1 GPa in order to assess the origin of the high conductivity anomalies observed in the middle to lower crustal levels. Dihedral angles of quartz-fluid-quartz determined from recovered samples were below 60, suggesting that fluid forms an interconnected network through the quartz aggregate. The electrical conductivity of quartzite increases with increasing temperature, which can be approximately expressed by Arrhenius equation. The apparent activation enthalpy decreases from 0.70 to 0.25 eV with increasing fluid fraction in volume from 0.00043 to 0.32. The electrical conductivity (sigma) of the fluid-bearing quartzite increased with fluid fraction (phi) proportionally to a power law (sigma proportional to phi(0.56-0.71)) within the temperature range of 900-1000K. The electrical conductivity of the aqueous fluid-bearing quartzite with the maximum fluid fraction (0.32) was found to be about three orders of magnitude higher than that of dry quartzite at 1000 K. However, its electrical conductivity was definitely lower than the geophysically observed values of high-conductivity anomalies, even if the quartzite contained large fluid fractions (0.32). The present results suggest that fluid-bearing quartzite is unable to account for the high-conductivity anomalies in terms of fluid fraction. A significant amount of other ionic species, such as Na, Cl, and Al in aqueous fluid, in addition to silica phases dissolved in fluid, is required to increase conductivity. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2012.03.007

その他リンク： http://orcid.org/0000-0002-5422-7396

Electrical conductivity of partial molten carbonate peridotite 査読

Takashi Yoshino, Elizabeth McIsaac, Mickael Laumonier, Tomoo Katsura

PHYSICS OF THE EARTH AND PLANETARY INTERIORS 194 1 - 9 2012年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

In order to investigate the effect of carbonate-content in partial melt on bulk conductivity under high pressure, electrical conductivity measurements were performed on carbonate melt-bearing peridotites using a Kawai-type multi-anvil apparatus. The starting materials were composed of spinet Iherzolite (KLB1) with small amounts of dolomite (1 and 3 wt.%). To obtain various melt fractions, annealing experiments were performed at different temperatures above 1400 K at 3 GPa. At low temperatures (<= 1500 K), the conductivity was distinctly higher than that of carbonate-free peridotite and close to that of the carbonatite melt-bearing olivine aggregates. Although the sample conductivity increased with increasing temperature, the rate at which the conductivity increases was small and the conductivity approached that of silicate melt-bearing peridotite. CO2 concentration in the partial melt decreased with increasing annealing temperature. Thus, the small increase of the conductivity with annealing temperature is attributed to a decrease of the melt conductivity due to a decrease in carbonate content in the partial melt. As the carbonate concentration in the melt decreases, the estimated melt conductivity approaches that of the basaltic melt. Therefore, conductivity enhancement by the carbonate-bearing melt is very effective at temperature just above that of the carbonate peridotite solidus. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2012.01.005

その他リンク： http://orcid.org/0000-0002-5422-7396

Static compression of (Mg-0.83,Fe-0.17)O and (Mg-0.75,Fe-0.25)O ferropericlase up to 58 GPa at 300, 700, and 1100 K 査読

Masanori Matsui, Eiji Ito, Daisuike Yamazaki, Takashi Yoshino, Xinzhuan Guo, Shuangming Shan, Yuji Higo, Ken-Ichi Funakoshi

AMERICAN MINERALOGIST 97 ( 1 ) 176 - 183 2012年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：MINERALOGICAL SOC AMER

Static compression data of (Mg-0.83,Fe-5.17)O and (Mg-0.75,Fe-0.25)O ferropericlases have been measured up to 58 GPa along 300, 700, and 1100 K isotherms, using synchrotron powder X-ray diffraction experiments combined with a Kawai-type, multi-anvil, high-pressure apparatus and sintered diamond anvils. High-temperature and high-pressure equations of state for these two ferropericlases, which have high-spin Fe2+ ions, were developed using measured compression data below 47 GPa, based on the Mie-Gruneisen relation and the Debye thermal model, combined with the 300 K Birch-Murnaghan equation. When the isothermal bulk modulus (K-0T) and the Debye temperature (Theta(0)) are fixed at 160 GPa and 500 K, respectively, the optimized equation-of-state parameters for these two phases are as follows: the pressure derivative of the bulk modulus (K-0T), the Gruneisen constant (gamma(0)), and the q parameter are 4.08 +/- 0.02, 1.53 +/- 0.04, and 0.7 +/- 0.2, respectively, for (Mg-0.83,Fe-0.17)O; and 4.22 +/- 0.03, 1.64 +/- 0.04, and 0.7 +/- 0.2, respectively, for (Mg-0.75,Fe-0.25)O. We found that calculated pressures with these equation-of-state parameters accurately reproduce the measured pressures of each ferropericlase below similar to 50 GPa for the isotherms of 300, 700, and 1100 K. Furthermore, the compression curve indicates that for each ferropericlase at each isothermal compression of 300, 700, and 1100 K, an abrupt volume reduction occurs at similar to 50 GPa. This volume reduction becomes more pronounced with increasing pressure, as a result of the progressive transition from high-spin to low-spin of the Fe2+ ions in each ferropericlase.

DOI： 10.2138/am.2012.3937

その他リンク： http://orcid.org/0000-0002-5422-7396

Experimental determination of carbon isotope fractionation between iron carbide melt and carbon: C-12-enriched carbon in the Earth's core? 査読

Madhusoodhan Satish-Kumar, Hayato So, Takashi Yoshino, Mutsumi Kato, Yoshikuni Hiroi

EARTH AND PLANETARY SCIENCE LETTERS 310 ( 3-4 ) 340 - 348 2011年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We report here new experimental data on equilibrium carbon isotope fractionation between graphite/diamond and iron carbide melt at 5 and 10 GPa and in the temperature range between 1200 and 2000 degrees C. Carbon isotope equilibrium was tested using morphological features of graphite and also by performing a longer duration experiment, both of which suggested that equilibrium carbon isotope fractionation is present. The results suggest that iron carbide melt will preferentially accumulate C-12 rather than C-13. An equilibrium temperature dependent fractionation between iron carbide melt and graphite/diamond is proposed based on the relation
Delta C-13((gr/dia - iron carbide melt)) = 8.85{10(6)/T-2(K)} + 0.99.
Our results are consistent with the carbon isotope distribution between graphite and cohenite (Fe3C) observed in iron meteorites. We propose that temperature-dependent fractionation of carbon isotopes between iron carbide melt and graphite/diamond might have created a "C-12-enriched core" with a significant difference in the distribution of carbon isotopes between the carbon in the metallic core and bulk silicate Earth during the accretion and differentiation of early Earth. Recent findings of low delta C-13 carbonados and diamonds of deep mantle origin supports the presence of a C-12 enriched source. The possible presence of a reservoir of C-12-enriched carbon in the Earth's core implies that it can generate large perturbations in the surface and shallow carbon-isotope system by the flux of lighter carbon from the core-mantle boundary. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.08.008

その他リンク： http://orcid.org/0000-0002-5422-7396

Electrical conductivity anisotropy of deformed talc rocks and serpentinites at 3 GPa 査読

Xinzhuan Guo, Takashi Yoshino, Ikuo Katayama

PHYSICS OF THE EARTH AND PLANETARY INTERIORS 188 ( 1-2 ) 69 - 81 2011年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The electrical conductivity anisotropy of deformed natural talc rocks and serpentinites was investigated using a Kawai-type multi-anvil press in the temperature range of 500-1000 K at 3 GPa. The electrical conductivities of the samples were measured by an impedance analyzer with a frequency range of 10(-3)-10(6) Hz along three sample directions: the direction parallel to the lineation of oriented minerals (x direction), the direction perpendicular to the lineation on the foliation plane (y direction), and the direction perpendicular to the foliation (z direction). For both rock types, electrical conductivities parallel to the x and the z directions were the highest and the lowest, respectively. Electrical conductivities of talc rocks and serpentinites were at least two orders of magnitude lower than previous reports. Electrical conductivities of the serpentinites were higher than those of the talc rocks. Electrical conductivity anisotropy for the talc rocks was stronger than that for the serpentinites at the same oxygen buffer condition. Electrical conductivity and its anisotropy of the serpentinites become higher with higher oxygen fugacity. The activation enthalpy of talc rocks was the lowest (0.59 eV) in the x direction and highest (0.68 eV) in the z direction. The activation enthalpies of the serpentinites in different directions show similar values: about 0.74 eV and 0.68 eV for the experiments using Mo and Ni electrodes, respectively. Impedance spectra for both rock types show the presence of two conduction paths: grain interior and grain boundary conductions. The total electrical conductivities were reduced by grain boundary conduction. Electrical conductivities of hydrous minerals show strong dependence on hydrogen concentration and hydrogen mobility. The conduction mechanism probably was proton migration through extrinsic vacancies derived from a presence of ferric iron perpendicular to the c axis of the crystals and through interstitial mechanisms parallel to the c axis. In both warm and cold subduction zones, high electrical conductors (similar to 10(-15) S/m) cannot be explained by the presence of talc or serpentinites. The electrical conductivity anisotropy in a subduction zone would be inconspicuously small (within one order) unless we consider other well aligned high conductive phases. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2011.06.012

その他リンク： http://orcid.org/0000-0002-5422-7396

Unstable graphite films on grain boundaries in crustal rocks 査読

Takashi Yoshino, Fumiya Noritake

EARTH AND PLANETARY SCIENCE LETTERS 306 ( 3-4 ) 186 - 192 2011年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The origin of high electrical conductive anomalies in the lower crust is a long-standing and controversial problem. Although it has been proposed that saturated saline water or partial melt increases electrical conductivity, graphite film has also been recognized as a potential cause of high conductivity since the discovery of fine graphite films on the grain boundaries of high-grade metamorphic rocks. To investigate the stability of graphite film on grain boundary of silicate minerals under lower crustal conditions, electrical conductivity of graphite film on synthetic grain boundaries of quartz bicrystals was measured by means of impedance spectroscopy at 1 GPa and up to 1200 K in a multianvil apparatus. At first heating, the electrical conductivity of the thin graphite film with thickness less than 100 nm was initially very high but decreased with time during annealing. Under high temperature conditions (>1000 K), the conductivity of a thin carbon film rapidly decreases and approaches the quartz conductivity. This indicates that graphite film on a grain boundary between two quartz crystals is not stable at high temperatures. Optical microscopic observation of the run products suggested a disconnected feature of graphite on a quartz grain boundary. Disconnection of graphite film can be caused by higher interfacial energy between graphite and silicate minerals than that of the grain boundary energy. Therefore, a thin graphite film is not a likely candidate to account for high conductivity anomalies in the middle and lower continental crust (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.04.003

その他リンク： http://orcid.org/0000-0002-5422-7396

Effect of iron content on electrical conductivity of ferropericlase with implications for the spin transition pressure 査読

Takashi Yoshino, Eiji Ito, Tomoo Katsura, Daisuke Yamazaki, Shuanming Shan, Xinzhuan Guo, Masayuki Nishi, Yuji Higo, Ken-ichi Funakoshi

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 116 ( 4 ) 2011年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

The pressure-induced electronic spin transition of iron in ferropericlase was investigated as a function of iron content in ferropericlase by in situ electrical conductivity measurement. The electrical conductivity of ferropericlase, (Mg1-x,Fe-x)O (x = 0.07, 0.10, 0.13, 0.17, 0.24), was measured up to 53 GPa and 600 K using the Kawai-type multianvil apparatus equipped with sintered diamond anvils. At pressures up to 25 GPa, the electrical conductivity of ferropericlase generally increases with increasing pressure, and both the activation energy and activation volume of ferropericlase decrease with increasing iron content. For the samples with x = 0.07 and 0.10, the electrical conductivity shows a slight initial decrease and becomes constant between 25 and 40 GPa, upon which it increases slightly as the pressure increases. For the samples with higher iron content, the electrical conductivity constantly increases with pressure over the investigated pressure range. If these changes in the electrical conductivity are due to the isosymmetric high-to low-spin transition of iron in ferropericlase, this conductivity change suggests that the spin transition pressure significantly decreases with decreasing iron content in ferropericlase. Because the amount of iron in ferropericlase that coexists with the Al-bearing perovskite seems to be less than that in the Al-free perovskite, the influence of the iron partitioning between perovskite and ferropericlase by the spin transition appears in a pressure range of about 30-40 GPa in the lower mantle of the Earth.

DOI： 10.1029/2010JB007801

その他リンク： http://orcid.org/0000-0002-5422-7396

Phase boundary between perovskite and post-perovskite structures in MnGeO3 determined by in situ X-ray diffraction measurements using sintered diamond anvils 査読

Daisuke Yamazaki, Eiji Ito, Tomoo Katsura, Takashi Yoshino, Shuangmeng Zhai, Hiroshi Fukui, Anton Shatskiy, Xinzhuan Guo, Shuangming Shan, Takuo Okuchi, Yoshinori Tange, Yuji Higo, Ken-ichi Funakoshi

AMERICAN MINERALOGIST 96 ( 1 ) 89 - 92 2011年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：MINERALOGICAL SOC AMER

To determine the phase boundary between the perovskite and post-perovskite structures in MnGeO3, in situ X-ray observations were carried out at pressures of 57-68 GPa and temperatures of 1000-1900 K using the Kawai-type high-pressure apparatus equipped with sintered diamond anvils interfaced with synchrotron radiation. The phase boundary was determined to be P (GPa) = 39.2 + 0.013T (K) based on Tsuchiya's (2003) gold pressure scale. The Clapeyron slope, dP/dT, of 13(+12/-5) MPa/K, determined in the present study is larger that of MgGeO3 and MgSiO3.

DOI： 10.2138/am.2011.3499

その他リンク： http://orcid.org/0000-0002-5422-7396

Grain growth kinetics of majorite and stishovite in MORB 査読

Daisuke Yamazaki, Takuya Matsuzaki, Takashi Yoshino

PHYSICS OF THE EARTH AND PLANETARY INTERIORS 183 ( 1-2 ) 183 - 189 2010年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Grain growth rates of majorite and stishovite, in their aggregates with MORB composition, were studied at 18 GPa and temperatures ranging from 1873 to 2223 K. The rates of grain growth were expressed by G(n) - G(0)(n) = k(0)t exp(-H*/RT) where G is the grain size at time t (s), and G(0) is the initial grain size. We determined the grain growth kinetic parameters for majorite, where n = 9.1 +/- 1.3, H-* = 950 +/- 249 kJ/mol, and log k(0) = -32.5 +/- 2.3 m(9.1)/s for the graphite capsule and log k(0) = -31.3 +/- 3.9 m(9.1)/s for the Re capsule. Kinetic parameters for stishovite were determined to be n = 6.6 +/- 0.9, H-* = 599 +/- 226 kJ/mol, and log k(0) = -30.6 +/- 0.9 m(6.6)/s for the graphite capsule and log k(0) = -29.0 +/- 1.1 m(6.6)/s for the Re capsule. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2010.09.009

その他リンク： http://orcid.org/0000-0002-5422-7396

Adiabatic temperature profile in the mantle 査読

Tomoo Katsura, Akira Yoneda, Daisuke Yamazaki, Takashi Yoshino, Eiji Ito

PHYSICS OF THE EARTH AND PLANETARY INTERIORS 183 ( 1-2 ) 212 - 218 2010年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The temperature at the 410-km discontinuity is re-evaluated by comparing the depth of the discontinuity with the olivine-wadsleyite transition pressure obtained using in situ X-ray diffraction experiments by Katsura et al. (2004a) and equation of state (EoS) of MgO by Tange et al. (2009) (Tange scale) and Matsui et al. (2000). The newly estimated temperature is 1830 +/- 48 K, 70 K higher than that by our previous estimation. The EoSes of the major mantle minerals (olivine, wadsleyite, ringwoodite and perovskite) are also recalculated using the Tange scale. The adiabatic temperature gradient is calculated using the thermal expansion coefficient obtained from these EoSes. The adiabatic temperature gradient gradually decreases with increasing depth without a phase transition, and abruptly increases in association with phase transitions. The adiabatic temperature gradients are found to be 04-0.5 and 0.3 K/km in the upper and lower parts of the mantle, respectively. The temperatures at a depth of 200 km, the bottom of the mantle transition zone, the top of the lower mantle and a depth of 2700 km are found to be 1720 +/- 40, 2010 +/- 40, 1980 +/- 40, and 2730 +/- 50 K. The mantle potential temperature is found to be 1610 +/- 35 K. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2010.07.001

その他リンク： http://orcid.org/0000-0002-5422-7396

Anisotropy of synthetic quartz electrical conductivity at high pressure and temperature 査読

Duojun Wang, Heping Li, Li Yi, Takuya Matsuzaki, Takashi Yoshino

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 115 ( 9 ) 2010年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

AC measurements of the electrical conductivity of synthetic quartz along various orientations were made between 0.1 and 1 MHz, at similar to 855 similar to 1601 K and at 1.0 GPa. In addition, the electrical conductivity of quartz along the c axis has been studied at 1.0-3.0 GPa. The impedance arcs representing bulk conductivity occur in the frequency range of 10(3)-10(6) Hz, and the electrical responses of the interface between the sample and the electrode occur in the 0.1 similar to 10(3) Hz range. The pressure has a weak effect on the electrical conductivity. The electrical conductivity experiences no abrupt change near the alpha - beta phase transition point. The electrical conductivity of quartz is highly anisotropic; the electrical conductivity along the c axis is strongest and several orders of magnitude larger than in other directions. The activation enthalpies along various orientations are determined to be 0.6 and 1.2 eV orders of magnitude, respectively. The interpretation of the former is based on the contribution of alkali ions, while the latter effect is attributed to additional unassociated aluminum ions. Comparison of determined anisotropic conductivity of quartz determined with those from field geophysical models shows that the quartz may potentially provide explanations for the behavior of electrical conductivity of anisotropy in the crust that are inferred from the transverse magnetic mode.

DOI： 10.1029/2009JB006695

その他リンク： http://orcid.org/0000-0002-5422-7396

Electrical conductivity of basaltic and carbonatite melt-bearing peridotites at high pressures: Implications for melt distribution and melt fraction in the upper mantle 査読

Takashi Yoshino, Mickael Laumonier, Elizabeth McIsaac, Tomoo Katsura

EARTH AND PLANETARY SCIENCE LETTERS 295 ( 3-4 ) 593 - 602 2010年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Electrical impedance measurements were performed on two types of partial molten samples with basaltic and carbonatitic melts in a Kawai-type multi-anvil apparatus in order to investigate melt fraction-conductivity relationships and melt distribution of the partial molten mantle peridotite under high pressure. The silicate samples were composed of San Carlos olivine with various amounts of mid-ocean ridge basalt (MORB), and the carbonate samples were a mixture of San Carlos olivine with various amounts of carbonatite. High-pressure experiments on the silicate and carbonate systems were performed up to 1600 K at 1.5 GPa and up to at least 1650 K at 3 GPa, respectively. The sample conductivity increased with increasing melt fraction. Carbonatite-bearing samples show approximately one order of magnitude higher conductivity than basalt-bearing ones at the similar melt fraction. A linear relationship between log conductivity (sigma(bulk)) and log melt fraction (phi) can be expressed well by the Archie's law (Archie, 1942) (sigma(bulk)/sigma(melt)=C phi(n)) with parameters C = 0.68 and 0.97, n = 0.87 and 1.13 for silicate and carbonate systems, respectively. Comparison of the electrical conductivity data with theoretical predictions for melt distribution indicates that the model assuming that the grain boundary is completely wetted by melt is the most preferable melt geometry. The gradual change of conductivity with melt fraction suggests no permeability jump due to melt percolation at a certain melt fraction. The melt fraction of the partial molten region in the upper mantle can be estimated to be 1-3% and similar to 0.3% for basaltic melt and carbonatite melt, respectively. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2010.04.050

その他リンク： http://orcid.org/0000-0002-5422-7396

Pressure generation and investigation of the post-perovskite transformation in MgGeO3 by squeezing the Kawai-cell equipped with sintered diamond anvils 査読

Eiji Ito, Daisuke Yamazaki, Takashi Yoshino, Hiroshi Fukui, Shuangmeng Zhai, Anton Shatzkiy, Tomoo Katsura, Yoshinori Tange, Ken-ichi Funakoshi

EARTH AND PLANETARY SCIENCE LETTERS 293 ( 1-2 ) 84 - 89 2010年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

High pressure generation has been tried by using the Kawai-cell equipped with sintered diamond cubes and the synchrotron radiation at SPring-8. The maximum attainable pressure reached 90.4 GPa at 300 K based on the Anderson et al. (1989) Au scale. Simultaneously, we investigated the perovskite (Pv)-postperovskite (PPv) transformation in MgGeO3 up to ca. 74 GPa and 2200 K by means of in situ X-ray diffraction method. Transformation from Pv to PPv was observed at pressures and temperatures higher than 63 GPa and 1300 K. Both the forward and the reverse reactions were found to be fairly sluggish over the examined temperature range. We determined the phase boundary by passing through the conditions at which either Pv or PPv phase grew and that of coexistence of both the phases, which is expressed by the equation T(K) = 177 P (GPa) - 9677. Our dP/dT slope of 5.6 MPa/K for MgGeO3 is close to the minimum estimate for MgSiO3 and accordingly suggests relatively deeper D '' discontinuity and a high heat flux from the core. We emphasize that the phase boundary completely relies on the pressure scale adopted. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2010.02.023

その他リンク： http://orcid.org/0000-0002-5422-7396

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