担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

We conducted in situ high-pressure acoustic-wave velocity measurements of Fe2+-bearing MgSiO3 glass up to 158 GPa by Brillouin scattering spectroscopy to clarify the effect of iron on the elasticity and structural evolution of silicate melts in the lower mantle. The change in trend of the V-S profile, likely induced by the structural transition of Si-O coordination number from 6 to 6+ proposed in previous studies of silicate glasses, was confirmed to be located at similar to 106 GPa. Given the iron contents of partial melts derived from a pyrolitic or chondritic mantle, the transition pressure would be at around 84-97 GPa, which is well within the lowermost-mantle pressure regime. Our data show the substitution of 12 mol% Fe in MgSiO3 glass decreases the V-S by similar to 5.5%. This implies that iron affects the buoyancy relations between melts/crystals and the melts at the lowermost mantle will have the higher coordination number than 6.

DOI： 10.1029/2022gl098279

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

Determination of the chemical composition of the Earth's mantle is of prime importance to understand the evolution, dynamics, and origin of the Earth. However, there is a lack of experimental data on sound velocity of iron-bearing Bridgmanite (Brd) under relevant high-pressure conditions of the whole mantle, which prevents constraints on the mineralogical model of the lower mantle. To uncover these issues, we have conducted sound-velocity measurement of iron-bearing Brd in a diamond-anvil cell (DAC) up to 124 GPa using Brillouin scattering spectroscopy. Here we show that the sound velocities of iron-bearing Brd throughout the whole pressure range of lower mantle exhibit an apparent linear reduction with the iron content. Our data fit remarkably with the seismic structure throughout the lower mantle with Fe2+-enriched Brd, indicating that the greater part of the lower mantle could be occupied by Fe2+-enriched Brd. Our lower-mantle model shows a distinctive Si-enriched composition with Mg/Si of 1.14 relative to the upper mantle (Mg/Si = 1.25), which implies that the mantle convection has been inefficient enough to chemically homogenize the Earth's whole mantle.

DOI： 10.1073/pnas.1917096117

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担当区分：筆頭著者   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  

© 2019 Elsevier B.V. Phase relations, including the eutectic liquid composition in the Fe–C binary system, remain unclear under the core pressure range, which makes estimating the carbon budget in the Earth's core difficult. To explore this issue, we have conducted melting and subsolidus experiments on Fe–C alloys in a diamond-anvil cell up to 255 GPa. Textural and compositional characterizations of quenched samples show that carbon concentration in the eutectic liquid slightly decreases with increasing pressure and is about 3 wt.% at the inner core boundary (ICB) pressure. The solubility of carbon in solid Fe is found to be almost constant at ∼1.0 wt.%. In situ X-ray diffraction data indicate that Fe forms eutectic melting with Fe 3 C to 203 GPa and with Fe 7 C 3 at 255 GPa. Previous studies on liquid Fe–C alloys suggested that the density of the outer core is explained by liquid Fe containing 1.8 to 4.2 wt.% C. If the liquid core includes <3 wt.% C as a single light element, hexagonal close-packed (hcp) Fe crystallizes at the ICB. However, the carbon content in such solid Fe is ≤1 wt.%, less than that required to account for the inner core density deficit from pure iron. When the outer core includes ≥3 wt.% C, it forms Fe 7 C 3 at the ICB, whose density is too small for the inner core. Carbon is therefore not a primary light element in the core. Nevertheless, the outer core liquid can be Fe–C–Si, Fe–C–S, or Fe–C–H. Such core liquid crystallizes solid Fe with light elements including less than 1 wt.% C, which may explain the density and the sound velocities observed in the inner core.

DOI： 10.1016/j.epsl.2019.03.020

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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  

©2016. American Geophysical Union. All Rights Reserved. Recent studies show that δ-AlOOH is stable up to the base of the mantle. This phase is, therefore, a possible carrier and host of water in the deep mantle. To uncover the physical properties of δ-AlOOH under deep mantle pressure conditions, we have conducted high-pressure acoustic wave velocity measurements of δ-AlOOH by using Brillouin spectroscopy combined with high-pressure Raman spectroscopic measurements in a diamond anvil cell up to pressures of 134 GPa. There is a precipitous increase by ∼14% in the acoustic velocities of δ-AlOOH from 6 to 15 GPa, which suggests that pressure-induced O-H bond symmetrization occurs in this pressure range. The best fit values for the high-pressure form of δ-AlOOH of K0 = 190 (2) (GPa), G0 = 160.0 (9) (GPa), (∂K/∂P)0 = K0′ = 3.7 (1), and (∂G/∂P)0 = G0′ = 1.32 (1) indicate that δ-AlOOH has a 20-30% higher VS value compared to those of the major constituent minerals in the mantle transition zone, such as wadsleyite, ringwoodite, and majorite. On the other hand, the VS of δ-AlOOH is ∼7% lower than that of Mg-bridgmanite under lowermost mantle pressure conditions because of the significantly lower value of the pressure derivative of the shear modulus. By comparing our results with seismic observations, we can infer that δ-AlOOH could be one of the potential causes of a positive VS anomaly observed at ∼600 km depth beneath the Korean peninsula and a negative VS jump near 2800 km depth near the northern margin of the large low-shear-velocity province beneath the Pacific.

DOI： 10.1002/2015JB012477

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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 INST PHYSICS  

© 2021 Author(s). Semiconductor-based heaters for diamond anvil cells (DACs) have advantages over metal wire heaters in terms of repeated use and the ability to reach higher temperatures. We introduce a cylindrical SiC heater for an externally heated DAC (EHDAC) that works satisfactorily at temperatures up to 1500 K and pressures around 90 GPa. The heater is reusable and inexpensive, and only slight modifications to the DAC are required to fit the heater. Experiments on melting of NaCl and gold are conducted at ambient pressure to test the temperature accuracy of the EHDAC system, and resistance measurements on iodine at high pressures and temperatures are performed to assess the heater assembly. These test runs show that a uniform and accurate temperature can be maintained by the EHDAC assembly, which has potential applications to a variety of transport property measurements.

DOI： 10.1063/5.0036551

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：速報，短報，研究ノート等（大学，研究機関紀要）  

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：速報，短報，研究ノート等（大学，研究機関紀要）  

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：速報，短報，研究ノート等（大学，研究機関紀要）  

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記述言語：日本語   出版者・発行元：日本高圧力学会  

DOI： 10.4131/jshpreview.29.217

CiNii Article

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記述言語：日本語   出版者・発行元：日本惑星科学会  

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CiNii Books

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開催年月日： 2023年5月21日 - 2023年5月26日

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開催年月日： 2023年2月28日 - 2023年3月1日

会議種別：ポスター発表  

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開催年月日： 2022年5月22日 - 2022年6月3日

会議種別：ポスター発表  

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開催年月日： 2021年7月26日 - 2021年7月30日

記述言語：英語   会議種別：口頭発表（一般）  

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開催年月日： 2018年12月

記述言語：英語   会議種別：口頭発表（一般）  

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