掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

DOI： 10.2138/am-2022-8546

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

Abstract

Fe,Al-bearing MgSiO3 perovskite (bridgmanite) is considered to be the most abundant mineral in Earth’s lower mantle, hosting ferric iron in its structure as charge-coupled (Fe2O3 and FeAlO3) and vacancy components (MgFeO2.5 and Fe2/3SiO3). We examined concentrations of ferric iron and aluminum in the perovskite phase as a function of temperature (1700–2300 K) in the MgSiO3-FeAlO3-MgO system at 27 GPa using a multi-anvil high-pressure apparatus. We found a LiNbO3-structured phase in the quenched run product, which was the perovskite phase under high pressures and high temperatures. The perovskite phase coexists with corundum and a phase with (Mg,Fe3+,☐)(Al,Fe3+)2O4 composition (☐ = vacancy). The FeAlO3 component in the perovskite phase decreases from 69 to 65 mol% with increasing temperature. The Fe2O3 component in the perovskite phase remains unchanged at ~1 mol% with temperature. The A-site vacancy component of Fe2/3SiO3 in the perovskite phase exists as 1–2 mol% at 1700–2000 K, whereas 1 mol% of the oxygen vacancy component of MgFeO2.5 appears at higher temperatures, although the analytical errors prevent definite conclusions. The A-site vacancy component might be more important than the oxygen vacancy component for the defect chemistry of bridgmanite in slabs and for average mantle conditions when the FeAlO3 charge-coupled component is dominant.

DOI： 10.2138/am-2022-8457

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

DOI： 10.1029/2022jb026291

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その他リンク： https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2022JB026291

掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acsearthspacechem.2c00326

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担当区分：最終著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

Abstract

The stability of Fe5O6 has been experimentally determined under pressure-temperature conditions relevant for the Earth’s deeper upper mantle down to the upper portion of the lower mantle (to 28 GPa). In addition, we investigated the incorporation of Mg into Fe5O6 and its systematics, which allows us to discuss the relevance of this phase for the mantle. Experiments were performed from 8–28 GPa and 900–1600 °C. Additional oxide phases may appear if the bulk composition does not maintain the Fe32+Fe23+O6 stoichiometry during the experiment, including coexisting Fe4O5 or Fe9O11. Unfortunately, the similarities in Raman spectra between several high-pressure Fe-oxide phases make this method unsuitable for distinguishing which phase is present in a given sample. The stability field for Fe5O6 extends from ~9 to at least 28 GPa but is truncated at lower temperatures by the assemblage Fe4O5 + wüstite. Refined thermodynamic properties for Fe5O6 are presented. The range of redox stability of Fe5O6 appears to be more limited than that of Fe4O5.

Solid solution along the Fe5O6-Mg3Fe2O6 binary is quite limited, reaching a maximum Mg content of ~0.82 cations per formula unit (i.e., XMg3Fe2O6 ≈ 0.27) at 1400 °C and 10 GPa. The observed sharp decrease in molar volume of the O6-phase with Mg content could be a possible explanation for the limited range of solid solution. A phase diagram has been constructed for a composition of approximately Mg0.5Fe2.52+Fe23+O6 stoichiometry. This small amount of Mg causes a significant change in the relations between the O6-structured phase and the assemblage O5-structured phase + (Mg,Fe)O. Several experiments were performed to test whether the O6-phase can coexist with mantle silicates like wadsleyite and ringwoodite. In all cases, the run products contained (Mg,Fe)2Fe2O5 rather than the O6-phase, further underlining the limited ability of Fe5O6 to accommodate enough Mg to be stable in a mantle assemblage.

The large stability field of Fe5O6 implies that this phase could likely occur in locally Fe-rich environments, like those sampled by some “deep” diamonds. However, the limited solubility of Mg in the O6-phase leads us to conclude that the O5-phase should be of much more relevance as an accessory phase in a peridotitic mantle assemblage.

DOI： 10.2138/am-2022-8370

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

Abstract

Orthorhombic CaFe2O4-structured (Cf) Na-rich aluminous silicate (space group Pbnm) is a major mineral of metabasaltic rocks at lower mantle conditions and can, therefore, significantly affect the physical properties of subducted oceanic crusts. We attempted to synthesize single crystals of Cf-type phases in the systems NaAlSiO4, NaAlSiO4-MgAl2O4, NaAlSiO4-MgAl2O4-Fe3O4, and NaAlSiO4-MgAl2O4-Fe3O4-H2O at 23–26 GPa and 1100–2200 °C. Under dry conditions, single crystals of Cf-type phase up to 100–150 μm in size were recovered from 23 GPa and 2000–2200 °C. Single-crystal X-ray diffraction and composition analyses suggest that the synthesized Cf-type phases have a few percent of vacancies in the eightfold-coordinated site with Na, Mg, and Fe2+ and partially disordered Al and Si in the octahedral sites. Iron-bearing Cf-type phases have 32–34% Fe3+ that is hosted both in the octahedral sites and in the eightfold-coordinated site. In NaAlSiO4-MgAl2O4-Fe3O4-H2O system, no formation of Cf-type phase was observed at 24 GPa and 1100–2000 °C due to the formation of hydrous Na-rich melt and Al-rich oxides or hydroxides, suggesting the possible absence of Cf-type phase in the hydrous basaltic crust. The single-crystal syntheses of Cf-type phases will be useful for investigating their physical properties, potentially improving models of lower mantle structure and dynamics.

DOI： 10.2138/am-2022-8748

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

Abstract

Akimotoite, a MgSiO3 polymorph present in the lower transition zone within ultramafic portions of subducting slabs and potentially also in the ambient mantle, will partition some amount of Al, raising the question of how this will affect its crystal structure and properties. In this study, a series of samples along the MgSiO3-Al2O3 (akimotoite-corundum) solid solution have been investigated by means of single-crystal X-ray diffraction to examine their crystal chemistry. Results show a strong nonlinear behavior of the a- and c-axes as a function of Al content, which arises from fundamentally different accommodation mechanisms in the akimotoite and corundum structures. Furthermore, two Al2O3-bearing akimotoite samples were investigated at high pressure to determine the different compression mechanisms associated with Al substitution. Al2O3-bearing akimotoite becomes more compressible at least up to 20 mol% Al2O3, due likely to an increase in compressibility as the Al cation is incorporated into the SiO6 octahedron. This observation is in strong contrast to the stiffer corundum end-member having a KT = 250 GPa, which is larger than that of the akimotoite end-member [KT = 205(1) GPa]. These findings have implications for mineral physics models of elastic properties, which have in the past assumed linear mixing behavior between the MgSiO3 akimotoite and Al2O3 corundum end-members to calculate sound wave velocities for Al-bearing akimotoite at high pressure and temperature.

DOI： 10.2138/am-2022-8257

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Proceedings of the National Academy of Sciences  

Water transported by subducted oceanic plates changes mineral and rock properties at high pressures and temperatures, affecting the dynamics and evolution of the Earth’s interior. Although geochemical observations imply that water should be stored in the lower mantle, the limited amounts of water incorporation in pyrolitic lower-mantle minerals suggest that water in the lower mantle may be stored in the basaltic fragments of subducted slabs. Here, we performed multianvil experiments to investigate the stability and water solubility of aluminous stishovite and CaCl ₂ -structured silica, referred to as poststishovite, in the SiO ₂ -Al ₂ O ₃ -H ₂ O systems at 24 to 28 GPa and 1,000 to 2,000 °C, representing the pressure–temperature conditions of cold subducting slabs to hot upwelling plumes in the top lower mantle. The results indicate that both alumina and water contents in these silica minerals increase with increasing temperature under hydrous conditions due to the strong Al ³⁺ -H ⁺ charge coupling substitution, resulting in the storage of water up to 1.1 wt %. The increase of water solubility in these hydrous aluminous silica phases at high temperatures is opposite of that of other nominally anhydrous minerals and of the stability of the hydrous minerals. This feature prevents the releasing of water from the subducting slabs and enhances the transport water into the deep lower mantle, allowing significant amounts of water storage in the high-temperature lower mantle and circulating water between the upper mantle and the lower mantle through subduction and plume upwelling. The shallower depths of midmantle seismic scatterers than expected from the pure SiO ₂ stishovite–poststishovite transition pressure support this scenario.

DOI： 10.1073/pnas.2211243119

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

Abstract

Elastic properties of B2‐Fe_0.67Ni_0.06Si_0.27 (15 wt.% Si) alloy have been investigated by combined high‐resolution inelastic X‐ray scattering and powder X‐ray diffraction in diamond anvil cells up to 100 GPa at room temperature. Densities (ρ), compressional (V_P) and shear (V_S) wave velocities were extrapolated to inner core conditions to enable comparison with the preliminary reference Earth model. The modeled aggregate compressional and shear wave velocities and densities of the two‐phase mixture of B2‐Fe_0.67Ni_0.06Si_0.27 and hcp‐Fe‐Ni are consistent with inner core PREM values of V_P,V_S, and ρ based on a linear mixing model with 30(5) vol % B2‐Fe_0.67Ni_0.06Si_0.27 and 70(5) vol % hcp Fe‐Ni, which corresponds to ∼3–5 wt.% Si and ∼5–12 wt.% Ni.

DOI： 10.1029/2021gl096405

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021GL096405

担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：MDPI AG  

The Clapeyron slope is the slope of a phase boundary in P–T space and is essential for understanding mantle dynamics and evolution. The phase boundary is delineating instead of balancing a phase transition’s normal and reverse reactions. Many previous high pressure–temperature experiments determining the phase boundaries of major mantle minerals experienced severe problems due to instantaneous pressure increase by thermal pressure, pressure drop during heating, and sluggish transition kinetics. These complex pressure changes underestimate the transition pressure, while the sluggish kinetics require excess pressures to initiate or proceed with the transition, misinterpreting the phase stability and preventing tight bracketing of the phase boundary. Our recent study developed a novel approach to strictly determine phase stability based on the phase equilibrium definition. Here, we explain the details of this technique, using the post-spinel transition in Mg2SiO4 determined by our recent work as an example. An essential technique is to observe the change in X-ray diffraction intensity between ringwoodite and bridgmanite + periclase during the spontaneous pressure drop at a constant temperature and press load with the coexistence of both phases. This observation removes the complicated pressure change upon heating and kinetic problem, providing an accurate and precise phase boundary.

DOI： 10.3390/min12070820

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

DOI： 10.1029/2022jb024556

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022JB024556

掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

Abstract

The experimental study of hydrogen-bonds and their symmetrization under extreme conditions is predominantly driven by diffraction methods, despite challenges of localising or probing the hydrogen subsystems directly. Until recently, H-bond symmetrization has been addressed in terms of either nuclear quantum effects, spin crossovers or direct structural transitions; often leading to contradictory interpretations when combined. Here, we present high-resolution in-situ ¹H-NMR experiments in diamond anvil cells investigating a range of systems containing linear O-H ⋯  O units at pressure ranges of up to 90 GPa covering their respective H-bond symmetrization. We found pronounced minima in the pressure dependence of the NMR resonance line-widths associated with a maximum in hydrogen mobility, precursor to a localisation of hydrogen atoms. These minima, independent of the chemical environment of the O-H ⋯  O unit, can be found in a narrow range of oxygen oxygen distances between 2.44 and 2.45 Å, leading to an average critical oxygen-oxygen distance of $${\bar{r } }_{ { { { { { { { \rm{OO } } } } } } } } }^{ { { { { { { { \rm{crit } } } } } } } } }=2.443(1)$$ Å.

DOI： 10.1038/s41467-022-30662-4

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その他リンク： https://www.nature.com/articles/s41467-022-30662-4

掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

DOI： 10.1007/s00269-022-01188-4

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その他リンク： https://link.springer.com/article/10.1007/s00269-022-01188-4/fulltext.html

掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

Abstract

SiC and (Fe, Mg)-silicide are candidate phases forming under reducing conditions in the Earth and planetary interiors. However, structural studies of SiC and Mg₂Si at high pressure and their thermal stability are presently lacking. In this work, we applied single-crystal X-ray diffraction in a diamond anvil cell at high pressure and determined the equations of state of α-SiC (6H) and βʹ-Mg₂Si_1.1 up to 60 and 40 GPa, respectively, yielding bulk moduli of 226.0(4) and 56(1) GPa. We also report the formation of a novel orthorhombic Mg₂Si₇ phase upon laser heating βʹ-Mg₂Si_1.1 at ~ 45 GPa and 2000 °C [Pbam, a = 7.16(1) Å, b = 12.490(3) Å, c = 2.6545(3) Å, V = 237.5(3) ų]. The structure of this compound contains layers formed by irregular 12-member silicon rings, which are arranged in channels filled with both Mg and Si atoms. No signs of the Mg₂Si₇ phase were detected upon releasing the pressure in the DAC, which suggests that this phase is unstable under ambient conditions.

DOI： 10.1007/s00269-022-01189-3

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その他リンク： https://link.springer.com/article/10.1007/s00269-022-01189-3/fulltext.html

担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.epsl.2022.117472

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.epsl.2022.117441

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掲載種別：研究論文（学術雑誌）   出版者・発行元：International Union of Crystallography (IUCr)  

Penetrating, high-energy synchrotron X-rays are in strong demand, particularly for high-pressure research in physics, chemistry and geosciences, and for materials engineering research under less extreme conditions. A new high-energy wiggler beamline P61 has been constructed to meet this need at PETRA III in Hamburg, Germany. The first part of the paper offers an overview of the beamline front-end components and beam characteristics. The second part describes the performance of the instrumentation and the latest developments at the P61B endstation. Particular attention is given to the unprecedented high-energy photon flux delivered by the ten wigglers of the PETRA III storage ring and the challenges faced in harnessing this amount of flux and heat load in the beam. Furthermore, the distinctiveness of the world's first six-ram Hall-type large-volume press, Aster-15, at a synchrotron facility is described for research with synchrotron X-rays. Additionally, detection schemes, experimental strategies and preliminary data acquired using energy-dispersive X-ray diffraction and radiography techniques are presented.

DOI： 10.1107/s1600577522001047

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

Abstract

The 660-kilometre seismic discontinuity is the boundary between the Earth’s lower mantle and transition zone and is commonly interpreted as being due to the dissociation of ringwoodite to bridgmanite plus ferropericlase (post-spinel transition)^1–3. A distinct feature of the 660-kilometre discontinuity is its depression to 750 kilometres beneath subduction zones^4–10. However, in situ X-ray diffraction studies using multi-anvil techniques have demonstrated negative but gentle Clapeyron slopes (that is,  the ratio between pressure and temperature changes) of the post-spinel transition that do not allow a significant depression^11–13. On the other hand, conventional high-pressure experiments face difficulties in accurate phase identification due to inevitable pressure changes during heating and the persistent presence of metastable phases^1,3. Here we determine the post-spinel and akimotoite–bridgmanite transition boundaries by multi-anvil experiments using in situ X-ray diffraction, with the boundaries strictly based on the definition of phase equilibrium. The post-spinel boundary has almost no temperature dependence, whereas the akimotoite–bridgmanite transition has a very steep negative boundary slope at temperatures lower than ambient mantle geotherms. The large depressions of the 660-kilometre discontinuity in cold subduction zones are thus interpreted as the akimotoite–bridgmanite transition. The steep negative boundary of the akimotoite–bridgmanite transition will cause slab stagnation (a stalling of the slab’s descent) due to significant upward buoyancy^14,15.

DOI： 10.1038/s41586-021-04157-z

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その他リンク： https://www.nature.com/articles/s41586-021-04157-z

掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

DOI： 10.1029/2021gl094185

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021GL094185

掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

DOI： 10.1038/s41586-021-04122-w

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その他リンク： https://www.nature.com/articles/s41586-021-04122-w

掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

DOI： 10.1063/5.0062525

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

Abstract

δ-AlOOH has emerged as a promising candidate for water storage in the lower mantle and could have delivered water into the bottom of the mantle. To date, it still remains unclear how the presence of iron affects its elastic, rheological, vibrational, and transport properties, especially across the spin crossover. Here, we conducted high-pressure X-ray emission spectroscopy experiments on a δ-(Al0.85Fe0.15) OOH sample up to 53 GPa using silicone oil as the pressure transmitting medium in a diamond-anvil cell. We also carried out laser Raman measurements on δ-(Al0.85Fe0.15)OOH and δ-(Al0.52Fe0.48)OOH up to 57 and 62 GPa, respectively, using neon as the pressure-transmitting medium. Evolution of Raman spectra of δ-(Al0.85Fe0.15)OOH with pressure shows two new bands at 226 and 632 cm−1 at 6.0 GPa, in agreement with the transition from an ordered (P21nm) to a disordered hydrogen bonding structure (Pnnm) for δ-AlOOH. Similarly, the two new Raman bands at 155 and 539 cm−1 appear in δ-(Al0.52Fe0.48)OOH between 8.5 and 15.8 GPa, indicating that the incorporation of 48 mol% FeOOH could postpone the order-disorder transition upon compression. On the other hand, the satellite peak (Kβ′) intensity of δ-(Al0.85Fe0.15)OOH starts to decrease at ~30 GPa and it disappears completely at 42 GPa. That is, δ-(Al0.85Fe0.15)OOH undergoes a gradual electronic spin-pairing transition at 30–42 GPa. Furthermore, the pressure dependence of Raman shifts of δ-(Al0.85Fe0.15)OOH discontinuously decreases at 32–37 GPa, suggesting that the improved hydrostaticity by the use of neon pressure medium could lead to a relatively narrow spin crossover. Notably, the pressure dependence of Raman shifts and optical color of δ-(Al0.52Fe0.48)OOH dramatically change at 41–45 GPa, suggesting that it probably undergoes a relatively sharp spin transition in the neon pressure medium. Together with literature data on the solid solutions between δ-AlOOH and ε-FeOOH, we found that the onset pressure of the spin transition in δ-(Al,Fe)OOH increases with increasing FeOOH content. These results shed new insights into the effects of iron on the structural evolution and vibrational properties of δ-AlOOH. The presence of FeOOH in δ-AlOOH can substantially influence its high-pressure behavior and stability at the deep mantle conditions and play an important role in the deep-water cycle.

DOI： 10.2138/am-2021-7541

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掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

DOI： 10.1063/5.0065879

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.pepi.2021.106786

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掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

DOI： 10.1063/5.0059279

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

Abstract

The phase relations of iron-rich olivine and its high-pressure polymorphs are important for planetary science and meteoritics because these minerals are the main constituents of terrestrial mantles and meteorites. The olivine–ahrensite binary loop was previously determined by thermochemical calculations in combination with high-pressure experiments; however, the transition pressures contained significant uncertainties. Here we determined the binary loop of the olivine–ahrensite transition in the (Mg,Fe)₂SiO₄ system at 1740 K in the pressure range of 7.5–11.2 GPa using a multi-anvil apparatus with the pressure determined using in situ X-ray diffraction, compositional analysis of quenched run products, and thermochemical calculation. Based on the determined binary loop, a user-friendly software was developed to calculate pressure from the coexisting olivine and ahrensite compositions. The software is used to estimate the shock conditions of several L6-type chondrites. The obtained olivine–ahrensite phase relations can also be applied for precise in-house multi-anvil pressure calibration at high temperatures.

DOI： 10.1007/s00410-021-01829-x

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その他リンク： https://link.springer.com/article/10.1007/s00410-021-01829-x/fulltext.html

掲載種別：研究論文（学術雑誌）   出版者・発行元：Copernicus GmbH  

Abstract. The formation of high-pressure oxyhydroxide phases spanned by the components AlOOH–FeOOH–MgSiO2(OH)2 in experiments suggests their capability to retain hydrogen in Earth's lower mantle. Understanding the vibrational properties of high-pressure phases provides the basis for assessing their thermal properties, which are required to compute phase diagrams and physical properties. Vibrational properties can be highly anisotropic, in particular for materials with crystal structures of low symmetry that contain directed structural groups or components. We used nuclear resonant inelastic X-ray scattering (NRIXS) to probe lattice vibrations that involve motions of 57Fe atoms in δ-(Al0.87Fe0.13)OOH single crystals. From the recorded single-crystal NRIXS spectra, we calculated projections of the partial phonon density of states along different crystallographic directions. To describe the anisotropy of central vibrational properties, we define and derive tensors for the partial phonon density of states, the Lamb–Mössbauer factor, the mean kinetic energy per vibrational mode, and the mean force constant of 57Fe atoms. We further show how the anisotropy of the Lamb–Mössbauer factor can be translated into anisotropic displacement parameters for 57Fe atoms and relate our findings on vibrational anisotropy to the crystal structure of δ-(Al,Fe)OOH. As a potential application of single-crystal NRIXS at high pressures, we discuss the evaluation of anisotropic thermal stresses in the context of elastic geobarometry for mineral inclusions. Our results on single crystals of δ-(Al,Fe)OOH demonstrate the sensitivity of NRIXS to vibrational anisotropy and provide an in-depth description of the vibrational behavior of Fe3+ cations in a crystal structure that may motivate future applications of NRIXS to study anisotropic vibrational properties of minerals.

DOI： 10.5194/ejm-33-485-2021

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

Abstract

We report the thermal Equation of State (EoS) of the non-magnetic Fe3C phase based on in situ X-ray diffraction (XRD) experiments to 117 GPa and 2100 K. High-pressure and temperature unit-cell volume measurements of Fe3C were conducted in a laser-heated diamond-anvil cell. Our pressure-volume-temperature (P-V-T) data together with existing data were fit to the Vinet equation of state with the Mie-Grüneisen-Debye thermal pressure model, yielding V0 = 151.6(12) Å3, K0 = 232(24) GPa, K0′= 5.09(46), γ0 = 2.3(3), and q = 3.4 (9) with θ0 = 407 K (fixed). The high-T data were also fit to the thermal pressure model with a constant αKT term, PTh = αKT(ΔT), and there is no observable pressure or temperature dependence, which implies minor contributions from the anharmonic and electronic terms. Using the established EoS for Fe3C, we made thermodynamic calculations on the P-T locations of the breakdown reaction of Fe3C into Fe7C3 and Fe. The reaction is located at 87 GPa and 300 K and 251 GPa and 3000 K. An invariant point occurs where Fe, Fe3C, Fe7C3, and liquid are stable, which places constraints on the liquidus temperature of the outer core, namely inner core crystallization temperature, as the inner core would be comprised by the liquidus phase. Two possible P-T locations for the invariant point were predicted from existing experimental data and the reaction calculated in this study. The two models result in different liquidus “phases” at the outer core-inner core boundary pressure: Fe3C at 5300 K and Fe7C3 at 3700 K. The Fe7C3 inner core can account for the density, as observed by seismology, while the Fe3C inner core cannot. The relevance of the system Fe-C to Earth’s core can be resolved by constructing a thermodynamic model for melting relations under core conditions as the two models predict very different liquidus temperatures.

DOI： 10.2138/am-2021-7581

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

Abstract

Three single crystals of CaTi2O4 (CT)-type, CaFe2O4 (CF)-type, and new low-density CaFe2O4 (LD-CF) related MgAl2O4 were synthesized at 27 GPa and 2500 °C and also CT-type MgAl2O4 at 45 GPa and 1727 °C using conventional and advanced multi-anvil technologies, respectively. The structures of CT-type and LD-CF related MgAl2O4 were analyzed by single-crystal X-ray diffraction. The lattice parameters of the CT-type phases synthesized at 27 and 45 GPa were a = 2.7903(4), b = 9.2132(10), and c = 9.3968(12) Å, and a = 2.7982(6), b = 9.2532(15), and c = 9.4461(16) Å, respectively, (Z = 4, space group: Cmcm) at ambient conditions. This phase has an AlO6 octahedral site and an MgO8 bicapped trigonal prism with two longer cation-oxygen bonds. The LD-CF related phase has a novel structure with orthorhombic symmetry (space group: Pnma), and lattice parameters of a = 9.207(2), b = 3.0118(6), and c = 9.739(2) Å (Z = 4). The structural framework comprises tunnel-shaped spaces constructed by edge- and corner-sharing of AlO6 and a 4+1 AlO5 trigonal bipyramid, in which MgO5 trigonal bipyramids are accommodated. The CF-type MgAl2O4 also has the same space group of Pnma but a slightly different atomic arrangement, with Mg and Al coordination numbers of 8 and 6, respectively. The LD-CF related phase has the lowest density of 3.50 g/cm3 among MgAl2O4 polymorphs, despite its high-pressure synthesis from the spinel-type phase (3.58 g/cm3), indicating that the LD-CF related phase formed via back-transformation from a high-pressure phase during the recovery. Combined with the previously determined phase relations, the phase transition between CF-and CT-type MgAl2O4 is expected to have a steep Clapeyron slope. Therefore, CT-type phase may be stable in basaltic- and continental-crust compositions at higher temperatures than the average mantle geotherm in the wide pressure range of the lower mantle. The LD-CF related phase could be found in shocked meteorites and used for estimating shock conditions.

DOI： 10.2138/am-2021-7619

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

DOI： 10.1038/s41561-021-00756-7

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その他リンク： https://www.nature.com/articles/s41561-021-00756-7

掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

DOI： 10.1029/2020gl087607

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020GL087607

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

DOI： 10.1029/2020gl087490

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020GL087490

掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

DOI： 10.1029/2020gl087036

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020GL087036

掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

DOI： 10.1029/2019jb018447

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2019JB018447

担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：The Japan Society of High Pressure Science and Technology  

DOI： 10.4131/jshpreview.30.156

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：The Crystallographic Society of Japan  

DOI： 10.5940/jcrsj.61.205

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

DOI： 10.1038/s41561-019-0452-1

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その他リンク： http://www.nature.com/articles/s41561-019-0452-1

掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

Abstract

The oxygen fugacity in the interior of the Earth is largely controlled by iron-bearing minerals. Recent studies have reported various iron oxides with chemical compositions between FeO and Fe3O4 above ~10 GPa. However, the stabilities of these high-pressure iron oxides remain mostly uninvestigated. In this study, we performed in situ X-ray diffraction (XRD) measurements in a laser-heated diamond-anvil cell (DAC) to determine the phase relations in both Fe5O6 and Fe4O5 bulk compositions to 61 GPa and to 2720 K. The results show that Fe5O6 is a high-temperature phase stable above 1600 K and ~10 GPa, while FeO + Fe4O5 are formed at relatively low temperatures. We observed the decomposition of Fe5O6 into 2FeO + Fe3O4 above 38 GPa and the decomposition of Fe4O5 into FeO + h-Fe3O4 at a similar pressure range. The coexistence of FeO and Fe3O4 indicates that none of the recently discovered compounds between FeO and Fe3O4 (i.e., Fe5O6, Fe9O11, Fe4O5, and Fe7O9) are formed beyond ~40 GPa at 1800 K, corresponding to conditions in the shallow lower mantle. Additionally, as some superdeep diamonds have genetic links with these high-pressure iron oxides, our results give constraints on pressure and temperature conditions of their formation.

DOI： 10.2138/am-2019-7097

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担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.eng.2019.01.013

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

DOI： 10.1029/2018jb016749

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2018JB016749

担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acs.inorgchem.8b00810

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

Abstract

The 660-km seismic discontinuity, which is a significant structure in the Earth’s mantle, is generally interpreted as the post-spinel transition, as indicated by the decomposition of ringwoodite to bridgmanite + ferropericlase. All precise high-pressure and high-temperature experiments nevertheless report 0.5–2 GPa lower transition pressures than those expected at the discontinuity depth (i.e. 23.4 GPa). These results are inconsistent with the post-spinel transition hypothesis and, therefore, do not support widely accepted models of mantle composition such as the pyrolite and CI chondrite models. Here, we present new experimental data showing post-spinel transition pressures in complete agreement with the 660-km discontinuity depth obtained by high-resolution in situ X-ray diffraction in a large-volume high-pressure apparatus with a tightly controlled sample pressure. These data affirm the applicability of the prevailing mantle models. We infer that the apparently lower pressures reported by previous studies are experimental artefacts due to the pressure drop upon heating. The present results indicate the necessity of reinvestigating the position of mantle mineral phase boundaries previously obtained by in situ X-ray diffraction in high-pressure–temperature apparatuses.

DOI： 10.1038/s41598-018-24832-y

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その他リンク： https://www.nature.com/articles/s41598-018-24832-y

担当区分：最終著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

DOI： 10.2138/am-2018-6135

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.pepi.2017.10.005

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

DOI： 10.2138/am-2018-6646

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

DOI： 10.1002/2017jb014579

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

DOI： 10.2138/am-2017-6050

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掲載種別：研究論文（学術雑誌）   出版者・発行元：European Association of Geochemistry  

DOI： 10.7185/geochemlet.1739

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Informa UK Limited  

DOI： 10.1080/08957959.2017.1375491

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

DOI： 10.2138/am-2017-6153

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

DOI： 10.2138/am-2017-6027

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Wiley  

DOI： 10.1111/maps.12887

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1111/maps.12887

掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

DOI： 10.1007/s00269-016-0836-3

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その他リンク： http://link.springer.com/article/10.1007/s00269-016-0836-3/fulltext.html

担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

DOI： 10.1063/1.4941716

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

DOI： 10.2138/am-2015-4818

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記述言語：日本語   出版者・発行元：一般社団法人日本鉱物科学会  

高圧相Mg₂Cr₂O₅の回収試料を粉末X線および透過電顕で調べたところ，基本構造の指数の半整数位置付近に，分裂した新たな反射が生じるとの興味深い現象が観察された．調べた結果，これらの分裂した反射は，構造中に周期的に配列した反位相境界が形成されたことによって生じることが分かった．そこで，これら周期的な反位相境界の形成とこの相の高圧相転移の関係について，考察した．

DOI： 10.14824/jakoka.2015.0_70

CiNii Article

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担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

DOI： 10.2138/am.2014.4736

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society (APS)  

DOI： 10.1103/physrevb.88.205114

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.88.205114/fulltext

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.epsl.2012.09.019

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.pepi.2012.10.002

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

DOI： 10.1007/s00269-012-0534-8

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その他リンク： http://link.springer.com/article/10.1007/s00269-012-0534-8/fulltext.html

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.epsl.2011.06.023

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記述言語：英語   会議種別：口頭発表（招待・特別）  

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記述言語：英語  

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記述言語：英語   会議種別：口頭発表（招待・特別）  

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会議種別：口頭発表（一般）  

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記述言語：英語   会議種別：口頭発表（招待・特別）  

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会議種別：口頭発表（招待・特別）  

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記述言語：英語   会議種別：口頭発表（一般）  

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会議種別：口頭発表（一般）  

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会議種別：ポスター発表  

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会議種別：ポスター発表  

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会議種別：口頭発表（招待・特別）  

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会議種別：ポスター発表  

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会議種別：ポスター発表  

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記述言語：英語   会議種別：口頭発表（招待・特別）  

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記述言語：英語   会議種別：口頭発表（一般）  

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記述言語：英語   会議種別：口頭発表（一般）  

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会議種別：ポスター発表  

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