Springer Science and Business Media LLC Acta Medica Okayama 0010-7999 181 7 2026 Electrical conductivity of geikielite (MgTiO3) at lunar mantle conditions: the role of metastable defect states and thermal history 55 EN Takashi Yoshino Institute for Planetary Materials, Okayama University Daisuke Yamazaki Institute for Planetary Materials, Okayama University The electrical conductivity of geikielite (MgTiO3), the Mg endmember of the ilmenite group, was investigated at mantle pressures of 2 and 4.3 GPa and temperatures up to 1850 K using a Kawai-type multi-anvil apparatus. Electrical conductivity increases by more than seven orders of magnitude between 800 and 1700 K and exhibits two distinct conduction regimes separated by a transition at ~ 1500–1700 K. The high-temperature regime is characterized by large activation enthalpies (ΔH ≈ 1.8–2.3 eV), whereas the low-temperature regime shows much lower values (ΔH ≈ 0.19–0.31 eV). Stepwise annealing experiments reveal a pronounced thermal-history dependence: repeated heating to progressively higher maximum temperatures (Tmax) produces metastable conductivity states, enhancing low-temperature conductivity by up to six orders of magnitude and systematically reducing activation enthalpy. This behavior indicates activation and freezing-in of defect-related charge carriers. Negative activation volumes further support a hopping-type conduction mechanism. Although Ti³⁺ was not directly detected, the combination of reducing experimental conditions, Al³⁺ impurities (~ 0.35 wt% Al₂O₃), low activation energies, and strong thermal memory is most consistent with small-polaron hopping involving Ti³⁺–Ti⁴⁺ pairs. At lunar core–mantle boundary temperatures, geikielite reaches conductivities of 10¹–10² S/m, exceeding those of olivine and overlapping estimates for the lunar low-velocity zone. Our results demonstrate that solid-state Ti-rich oxides can produce high electrical conductivity without partial melting, providing new constraints on the thermochemical evolution and electromagnetic structure of the lunar interior. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 0342-1791 53 2 2026 High-pressure spectroscopic investigation of ε-FeOOH: toward a better understanding of pressure-induced hydrogen-bond symmetrization 18 EN Izumi Mashino Institute for Planetary Materials, Okayama University Shigeru Yamashita Institute for Planetary Materials, Okayama University Takashi Yoshino Institute for Planetary Materials, Okayama University High-pressure spectroscopic measurements of ε-FeOOH were conducted up to ~ 65 GPa at room temperature in diamond anvil cells. The pressure evolution of the Raman vibrational modes confirms that a hydrogen-bond-symmetrization-induced phase transition from P21nm to Pnnm occurs at ~ 18 GPa. Infrared (IR) spectroscopic measurements suggest that the Pnnm phase has a disordered hydrogen state, and no spectroscopic evidence for fully centered hydrogen bonds is observed within the investigated pressure range. Above ~ 45 GPa, Fe3+ in ε-FeOOH undergoes a high-spin to low-spin transition as indicated by a reduction of the unit cell volume, together with reductions in IR transmitted and Raman signals. These results demonstrate that ε‑FeOOH preserves a disordered hydrogen‑bond configuration up to at least 45 GPa, whereas δ-AlOOH transforms to a centered hydrogen-bond configuration at ~ 18 GPa. This compositional contrast suggests that Fe‑bearing oxyhydroxides follow a distinct evolution of hydrogen bonding under compression, providing insight into hydrogen behavior in deep Earth materials. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0012-821X 687 2026 Phase diagram of Fe-C-S ternary system under planetary core conditions 120087 EN Bin Zhao Institute for Planetary Materials, Okayama University Jintao Zhu Institute for Planetary Materials, Okayama University Daniele Antonangeli Muséum National d’Histoire Naturelle, Sorbonne Université, UMR CNRS 7590, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC Guillaume Morard Muséum National d’Histoire Naturelle, Sorbonne Université, UMR CNRS 7590, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC Qi Chen Center for Advanced Radiation Sources, University of Chicago Takashi Yoshino Institute for Planetary Materials, Okayama University High-pressure, high-temperature experiments were conducted to investigate melting relations and phase assemblages in the Fe-C-S ternary system at 5 and 15 GPa, covering a temperature range of 1300–1900 K, conditions directly relevant to the Moon’s and Mercury’s cores. At 1300 K, the system is primarily governed by Fe-S eutectic melting, exhibiting notable complexity in the carbon-rich and sulfur-poor regions. With increasing temperature, the phase diagram simplifies: at 5 GPa and 1700 K, the Fe-Fe₃C-FeS system features three regions (Fe+L, C + L, and L). Similar phase assemblages are observed at 15 GPa, with Fe7C3 and diamond replacing Fe3C and graphite, respectively. Extensive Fe+L, C + L, and L regions are observed at 1900 K.<br> For a Moon’s core composed of a Fe-C-S alloy, nearly pure Fe is the only viable inner core phase above 1700 K. Below this temperature, both Fe and Fe₃C are potential solid inner core phases, depending on carbon content; a two-phase solid inner core is also theoretically possible. The inferred compositions of the outer core suggest densities of 6200–7300 kg/m³, with tighter constraints for models featuring an Fe₃C core.<br> At Mercury-relevant pressures, either Fe or Fe₇C₃ may form the solid inner core, again depending on carbon content. If the inner core is nearly pure Fe, the liquid outer core density ranges from 7300 to 7900 kg/m³. In both scenarios, a “snow” regime is plausible, though with distinct settling times. The ternary phase diagram indicates that Mercury is likely to develop a structurally layered inner core during secular cooling.<br> No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 2662-4435 7 1 2026 Stability and distribution of dense hydrous magnesium silicates in the mantle transition zone under low water activity conditions 265 EN Yunke Song Key Laboratory of High-temperature and High-pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences Xinzhuan Guo State Key Laboratory of Critical Mineral Research and Exploration, Institute of Geochemistry, Chinese Academy of Sciences Kuan Zhai Key Laboratory of High-temperature and High-pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences Wei Guo State Key Laboratory of Geomicrobiology and Environmental Changes, School of Earth Sciences, China University of Geosciences (Wuhan) Takashi Yoshino Institute for Planetary Materials, Okayama University Water plays a central role in controlling the physical and chemical properties of Earth’s deep interior. It remains uncertain how water is stored in subducting slabs within the mantle transition zone, between depths of about 410 and 660 kilometers, and whether dense hydrous magnesium silicates act as major water carriers to greater depths. Here we report high-pressure and high-temperature laboratory experiments on the Mg-Si-H system at pressures of 16 and 21.5 GPa and a temperature of 1400 K to evaluate hydrous phase stability under transition zone conditions. We find that when bulk water content is below 1.22 wt%, H2O is predominantly incorporated into wadsleyite and ringwoodite rather than forming dense hydrous magnesium silicates. Because estimated water contents in subducted oceanic slabs are typically lower than one weight percent, formation of these silicates is unlikely, suggesting that the mantle transition zone may restrict large scale water transport into the lower mantle. No potential conflict of interest relevant to this article was reported.

American Geophysical Union (AGU) Acta Medica Okayama 0094-8276 53 5 2026 Electrical Conductivity of Amorphous and Molten CaCO3 at High Pressures and Its Implications for Mantle Conductivity Anomalies e2025GL119568 EN Bin Zhao Institute for Planetary Materials, Okayama University Takashi Yoshino Institute for Planetary Materials, Okayama University Qi Chen Center for Advanced Radiation Sources, The University of Chicago Tony Yu Center for Advanced Radiation Sources, The University of Chicago Dongzhou Zhang Center for Advanced Radiation Sources, The University of Chicago Bin Chen School of Ocean and Earth Science and Technology, University of Hawaii at Manoa Yanbin Wang Center for Advanced Radiation Sources, The University of Chicago Impedance spectrometry experiments have been conducted on CaCO3 up to 15 GPa and 2,100 K to identify its state under high pressure. The melting temperature of CaCO3 was also determined by the falling of a Re sphere observed via X-ray radiography. The phase transition from aragonite to the amorphous phase does not cause a leap in the Electrical conductivity (EC), while a drastic increase in the EC, by 1.5–2.0 log units, only occurs with the onset of melting. The EC of amorphous CaCO3 is comparable to other hydrous mantle minerals at similar pressure and temperature conditions. The required fraction of amorphous CaCO3 implies that it can be excluded from the potential origins responsible for the observed high EC anomalies in the upper mantle. If the conductivity anomalies are induced by the presence of carbonate, a low-degree melting of carbonate-bearing peridotite is anticipated. No potential conflict of interest relevant to this article was reported.

American Geophysical Union (AGU) Acta Medica Okayama 2169-9313 131 1 2026 Electrical Conductivity of Carbonatite Melts to 20 GPa: Constraints on Partial Melting Atop the 410‐km Discontinuity and in the Lower Mantle Transition Zone e2025JB033390 EN Bin Zhao Institute for Planetary Materials, Okayama University Jintao Zhu Institute for Planetary Materials, Okayama University Qi Chen Center for Advanced Radiation Sources, University of Chicago Takashi Yoshino Institute for Planetary Materials, Okayama University Deep-origin carbonatite melts are considered to be the products of partial-melting of the oceanic crust in the subduction zones. In this study, we conducted electrical conductivity (EC) measurements on two samples, the composition of which resemble the partial-melting products atop the 410-km discontinuity and in the lower part of the transition zone. The EC of carbonatite melts was investigated using impedance spectroscopy combined with a multi-anvil press up to 20 GPa. Pressure has a great effect on the EC of the carbonatite melts. While the EC dropped overall by 0.6 log unit from 3 to 20 GPa for varying compositions, the pressure effect becomes weaker above 10 GPa. The Hashin-Shtrikman mixing model indicates that melt fraction of 0–0.3 vol% is necessary to account for the EC atop the 410-km discontinuity beneath NE China, north Philippine Sea, north Pacific, and Australian craton. However, this value soars to 1–4.5 vol% for the lower part of the transition zone in the same regions, and further increases to 3.7–7.3 vol% for cold subduction regions if the slab surface temperature is 300 K lower. The difference in the needed melt fraction at different depths implies that the magnitude of partial melting is much larger in the lower part of the mantle transition zone, and it is thus likely to be the main barrier to the recycled carbonates towards the deep interior. No potential conflict of interest relevant to this article was reported.

Wiley Acta Medica Okayama 1086-9379 2025 The effect of pressure on dihedral angle between liquid Fe‐S and orthopyroxene: Implication for percolative core formation in planetesimals and planetary embryos EN Takumi Miura Department of Earth and Space Science, Osaka University Hidenori Terasaki Department of Earth Sciences, Okayama University Hyu Takaki Department of Earth Sciences, Okayama University Kotaro Kobayashi Department of Earth Sciences, Okayama University Geoffrey David Bromiley School of Geosciences, The University of Edinburgh Takashi Yoshino Institute for Planetary Materials, Okayama University During precursor stages of planet formation, many planetesimals and planetary embryos are considered to have differentiated, forming an iron-alloy core and silicate mantle. Percolation of liquid iron-alloy in solid silicates is one of the major possible differentiation processes in these small bodies. Based on the dihedral angles between Fe-S melts and olivine, a criterion for determining whether melt can percolate through a solid, it has been reported that Fe-S melt can percolate through olivine matrices below 3 GPa in an oxidized environment. However, the dihedral angle between Fe-S melts and orthopyroxene (opx), the second most abundant mineral in the mantles of small bodies, has not yet been determined. In this study, high-pressure and high-temperature experiments were conducted under the conditions of planetesimal and planetary embryo interiors, 0.5–5.0 GPa, to determine the effect of pressure on the dihedral angle between Fe-S melts and opx. Dihedral angles tend to increase with pressure, although the pressure dependence is markedly reduced above 4 GPa. The dihedral angle is below the percolation threshold of 60° at pressures below 1.0–1.5 GPa, indicating that percolative core formation is possible in opx-rich interiors of bodies where internal pressures are lower than 1.0–1.5 GPa. The oxygen content of Fe-S melt decreases with increasing pressure. High oxygen contents in Fe-S melt reduce interfacial tension between Fe-S melt and opx, resulting in reduced dihedral angles at low pressure. Combined with previous results for dihedral angle variation of the olivine/Fe-S system, percolative core formation possibly occurs throughout bodies up to a radius of 1340 km for an olivine-dominated mantle, and up to 770 km for an opx-dominated mantle, in the case of S-rich cores segregating under relatively oxidizing conditions. For mantles of small bodies in which abundant olivine and opx coexist, the mineral with the largest volume fraction and/or smallest grain size will allow formation of interconnected mineral channels, and, therefore, the wetting property of this mineral determines the wettability of the melt, that is, controls core formation. No potential conflict of interest relevant to this article was reported.

American Geophysical Union (AGU) Acta Medica Okayama 2169-9313 130 10 2025 Electrical Conductivity of Carbonated Hydrous Basaltic Melt: Implications for the Conductivity Anomaly Beneath the Ocean Floors e2025JB032215 EN Bin Zhao Institute for Planetary Materials, Okayama University Jintao Zhu Institute for Planetary Materials, Okayama University Jinze He Institute for Planetary Materials, Okayama University Takashi Yoshino Institute for Planetary Materials, Okayama University We measured the electrical conductivity of CO2 and H2O-bearing basaltic melts up to 1750 K at 2 GPa, corresponding to pressure around the lithosphere-asthenosphere boundary. The electrical conductivity of the dry and hydrous samples is comparable to those reported by previous studies on the Fe-free basaltic melt. The substantial CO2 can limit the water solubility in basaltic melt at 2 GPa. Both CO2 and H2O, which cannot completely dissolve in the melt, coexist as fluid phases, resulting in reduced electrical conductivity of the basaltic melt, which has a lower water content relative to the amount of volatile components in the bulk starting system. The activation enthalpy of basaltic melt is markedly higher than those of more evolved silicate melts, especially on the H2O-poor condition, due to the more enriched alkaline earth elements. The present results suggest that an overall melt fraction of 0.1–5.3 vol% is needed to account for the high electrical conductivity anomalies (10－1.3 to 10－0.3 S/m) beneath the oceanic plate near the East Pacific Rise and Cocos plate. However, for those regions where the electrical conductivity is extremely high (≥10－0.3 S/m), more than 6 wt% H2O is expected to incorporate to maintain a melt fraction that will not trigger mechanical instability. In turn, it requires a low CO2 budget or degree of carbonation within these regions. No potential conflict of interest relevant to this article was reported.

American Geophysical Union (AGU) Acta Medica Okayama 0094-8276 52 14 2025 Unraveling the Complex Features of the Seismic Scatterers in the Mid‐Lower Mantle Through Phase Transition of (Al, H)‐Bearing Stishovite e2024GL114146 EN Yingxin Yu Deep Space Exploration Laboratory, School of Earth and Space Sciences, University of Science and Technology of China Youyue Zhang Institute for Planetary Materials, Okayama University Luo Li Deep Space Exploration Laboratory, School of Earth and Space Sciences, University of Science and Technology of China Xinyue Zhang Deep Space Exploration Laboratory, School of Earth and Space Sciences, University of Science and Technology of China Denglei Wang Deep Space Exploration Laboratory, School of Earth and Space Sciences, University of Science and Technology of China Zhu Mao Deep Space Exploration Laboratory, School of Earth and Space Sciences, University of Science and Technology of China Ningyu Sun Deep Space Exploration Laboratory, School of Earth and Space Sciences, University of Science and Technology of China Yanyao Zhang Earth and Planetary Sciences, Stanford University Xinyang Li State Key Laboratory of High Pressure and Superhard Materials, College of Physics, Jilin University Wancai Li CAS Key Laboratory of Crust‐Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China Sergio Speziale GFZ German Research Centre for Geosciences Dongzhou Zhang GeoSoilEnviroCARS, University of Chicago Jung‐Fu Lin Department of Earth and Planetary Sciences, Jackson School of Geosciences, The University of Texas at Austin Takashi Yoshino Institute for Planetary Materials, Okayama University Small-scale scatterers observed in the mid-lower mantle beneath the subduction zones are thought to result from the phase transition of stishovite within subducted oceanic crusts. Here we investigate the phase transition of (Al, H)-bearing stishovite with four compositions at simultaneously high P-T conditions combining Raman spectroscopy and X-ray diffraction. These experimental results reveal that the incorporation of 0.01 a.p.f.u Al into stishovite with H/Al ratio of ∼1/3 lowers the transition pressure by 6.7(3) GPa. However, the Clapeyron slope of this transition is nearly unaffected by changes in the Al content and has a value of 12.2–12.5(3) MPa/K. According to our results, Al content variation ranging from 0 to 0.07 a.p.f.u in SiO2 can reasonably explain the depth distribution from 800 to 1,900 km of the seismic scatterers observed in the circum-Pacific region. These results deepen our understanding on the complex features of mid-lower mantle seismic scatterers and corresponding dynamic processes. No potential conflict of interest relevant to this article was reported.

Wiley Acta Medica Okayama 1086-9379 59 6 2024 Wetting property of Fe‐S melt in solid core: Implication for the core crystallization process in planetesimals 1314 1328 EN Shiori Matsubara Department of Earth Sciences, Graduate School of Science and Technology, Okayama University Hidenori Terasaki Department of Earth Sciences, Graduate School of Science and Technology, Okayama University Takashi Yoshino Institute for Planetary Materials, Okayama University Satoru Urakawa Department of Earth Sciences, Graduate School of Science and Technology, Okayama University Daisuke Yumitori Department of Earth Sciences, Graduate School of Science and Technology, Okayama University In differentiated planetesimals, the liquid core starts to crystallize during secular cooling, followed by the separation of liquid–solid phases in the core. The wetting property between liquid and solid iron alloys determines whether the core melts are trapped in the solid core or they can separate from the solid core during core crystallization. In this study, we performed high-pressure experiments under the conditions of the interior of small bodies (0.5–3.0 GPa) to study the wetting property (dihedral angle) between solid Fe and liquid Fe-S as a function of pressure and duration. The measured dihedral angles are approximately constant after 2 h and decrease with increasing pressure. The dihedral angles range from 30° to 48°, which are below the percolation threshold of 60° at 0.5–3.0 GPa. The oxygen content in the melt decreases with increasing pressure and there are strong positive correlations between the S + O or O content and the dihedral angle. Therefore, the change in the dihedral angle is likely controlled by the O content of the Fe-S melt, and the dihedral angle tends to decrease with decreasing O content in the Fe-S melt. Consequently, the Fe-S melt can form interconnected networks in the solid core. In the obtained range of the dihedral angle, a certain amount of the Fe-S melt can stably coexist with solid Fe, which would correspond to the “trapped melt” in iron meteorites. Excess amounts of the melt would migrate from the solid core over a long period of core crystallization in planetesimals. No potential conflict of interest relevant to this article was reported.

American Association for the Advancement of Science (AAAS) Acta Medica Okayama 2375-2548 8 13 2022 Viscosity of bridgmanite determined by in situ stress and strain measurements in uniaxial deformation experiments eabm1821 EN Noriyoshi Tsujino Institute for Planetary Materials, Okayama University Daisuke Yamazaki Institute for Planetary Materials, Okayama University Yu Nishihara Geodynamics Research Center, Ehime University Takashi Yoshino Institute for Planetary Materials, Okayama University Yuji Higo Japan Synchrotron Radiation Research Institute Yoshinori Tange Japan Synchrotron Radiation Research Institute To understand mantle dynamics, it is important to determine the rheological properties of bridgmanite, the dominant mineral in Earth’s mantle. Nevertheless, experimental data on the viscosity of bridgmanite are quite limited due to experimental difficulties. Here, we report viscosity and deformation mechanism maps of bridgmanite at the uppermost lower mantle conditions obtained through in situ stress-strain measurements of bridgmanite using deformation apparatuses with the Kawai-type cell. Bridgmanite would be the hardest among mantle constituent minerals even under nominally dry conditions in the dislocation creep region, consistent with the observation that the lower mantle is the hardest layer. Deformation mechanism maps of bridgmanite indicate that grain size of bridgmanite and stress conditions at top of the lower mantle would be several millimeters and ~105 Pa to realize viscosity of 1021–22 Pa·s, respectively. This grain size of bridgmanite suggests that the main part of the lower mantle is isolated from the convecting mantle as primordial reservoirs. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 1996-1944 14 19 2021 Electrical Resistivity of Cu and Au at High Pressure above 5 GPa: Implications for the Constant Electrical Resistivity Theory along the Melting Curve of the Simple Metals 5476 EN Innocent C. Ezenwa Institute for Planetary Materials, Okayama University Takashi Yoshino Institute for Planetary Materials, Okayama University The electrical resistivity of solid and liquid Cu and Au were measured at high pressures from 6 up to 12 GPa and temperatures & SIM;150 K above melting. The resistivity of the metals was also measured as a function of pressure at room temperature. Their resistivity decreased and increased with increasing pressure and temperature, respectively. With increasing pressure at room temperature, we observed a sharp reduction in the magnitude of resistivity at & SIM;4 GPa in both metals. In comparison with 1 atm data and relatively lower pressure data from previous studies, our measured temperature-dependent resistivity in the solid and liquid states show a similar trend. The observed melting temperatures at various fixed pressure are in reasonable agreement with previous experimental and theoretical studies. Along the melting curve, the present study found the resistivity to be constant within the range of our investigated pressure (6-12 GPa) in agreement with the theoretical prediction. Our results indicate that the invariant resistivity theory could apply to the simple metals but at higher pressure above 5 GPa. These results were discussed in terms of the saturation of the dominant nuclear screening effect caused by the increasing difference in energy level between the Fermi level and the d-band with increasing pressure. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 00346748 91 3 2020 Measurement of the Seebeck coefficient under high pressure by dual heating 035115 EN Takashi Yoshino Institute for Planetary Materials, Okayama University Ran Wang Institute for Planetary Materials, Okayama University Hitoshi Gomi Institute for Planetary Materials, Okayama University Yoshihisa Mori 3Department of Applied Science, Okayama University of Science This study presents a new method for measuring the Seebeck coefficient under high pressure in a multi-anvil apparatus. The application of a dual-heating system enables precise control of the temperature difference between both ends of the sample in a high-pressure environment. Two pairs of W–Re thermocouples were employed at both ends of the sample to monitor and control the temperature difference, and independent probes were arranged to monitor the electromotive force (emf) produced by temperature oscillation at a given target temperature. The temperature difference was controlled within 1 K during the resistivity measurements to eliminate the influence of the emf owing to a sample temperature gradient. The Seebeck measurement was successfully measured from room temperature to 1400 K and was obtained by averaging the two measured values with opposite thermal gradient directions (∼20 K). Thermoelectric properties were measured on disk-shaped p-type Si wafers with two different carrier concentrations as a reference for high Seebeck coefficients. This method is effective to determine the thermoelectric power of materials under pressure. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0012821X 530 2019 Grain boundary diffusion of W in lower mantle phase with implications for isotopic heterogeneity in oceanic island basalts by core-mantle interactions 115887 EN Takashi Yoshino Institute for Planetary Materials, Okayama University Yoshiki Makino Geochemical Research Center, The University of Tokyo Toshihiro Suzuki Geochemical Research Center, The University of Tokyo Takafumi Hirata Geochemical Research Center, The University of Tokyo Tungsten isotopes provide important constraints on the ocean-island basalt (OIB) source regions. Recent analyses of μ182W in modern basalts with high 3He/4He originating from the core-mantle boundary region reveal two distinct features: positive μ182W in Phanerozoic flood basalts indicating the presence of primordial reservoir, and negative μ182W in modern OIBs. One possibility to produce large variations in μ182W is interaction between the mantle and outer core. Here, we report grain boundary diffusion of W in lower mantle phases. High pressure experimental results show that grain boundary diffusion of W is fast and strongly temperature dependent. Over Earth's history, diffusive transport of W from the core to the lowermost mantle may have led to significant modification of the W isotopic composition of the lower mantle at length scales exceeding one kilometer. Such grain boundary diffusion can lead to large variations in μ182W in modern basalts as a function of the distance of their source regions from the core mantle boundary. Modern oceanic island basalts from Hawaii, Samoa and Iceland exhibit negative μ182W and likely originated from the modified isotope region just above the core-mantle boundary, whereas those with positive μ182W could be derived from the thick Large Low Shear Velocity Provinces (LLSVPs) far from the core-mantle boundary (CMB). When highly-oxidized slabs accumulate at the CMB oxidizing the outer core at the interface, a large W flux with negative μ182W can be added to the silicate mantle. As a result, the source region of the OIB would be effectively modified to a negative μ182W. No potential conflict of interest relevant to this article was reported.

American Physical Society Acta Medica Okayama 2469-9950 100 21 2019 Resistivity, Seebeck coefficient, and thermal conductivity of platinum at high pressure and temperature 214302 EN Hitoshi Gomi Institute for Planetary Materials, Okayama University Takashi Yoshino Institute for Planetary Materials, Okayama University Platinum (Pt) is one of the most widely used functional materials for high-pressure and high-temperature experiments. Despite the crucial importance of its transport properties, both experimental and theoretical studies are very limited. In this study, we conducted density functional theory calculations on the electrical resistivity, the Seebeck coefficient, and the thermal conductivity of solid face-centered cubic Pt at pressures up to 200 GPa and temperatures up to 4800 K by using the Kubo-Greenwood formula. The thermal lattice displacements were treated within the alloy analogy, which is represented by means of the Korringa-Kohn-Rostoker method with the coherent potential approximation. The electrical resistivity decreases with pressure and increases with temperature. These two conflicting effects yield a constant resistivity of similar to 70 mu Omega cm along the melting curve. Both pressure and temperature effects enhance the thermal conductivity at low temperatures, but the temperature effect becomes weaker at high temperatures. Although the pressure dependence of the Seebeck coefficient is negligibly small at temperatures below similar to 1500 K, it becomes larger at higher temperatures. It requires a calibration of a thermocouple such as Pt-Rh in high-pressure and -temperature experiments. No potential conflict of interest relevant to this article was reported.

Mineralogical Society of America Acta Medica Okayama 0003-004X 103 8 2018 The effects of ferromagnetism and interstitial hydrogen on the equation of states of hcp and dhcp FeHx: Implications for the Earth's inner core age 1271 1281 EN Hitoshi Gomi Institute for Planetary Materials, Okayama University Yingwei Fei Geophysical Laboratory, Carnegie Institution of Washington Takashi Yoshino Institute for Planetary Materials, Okayama University Hydrogen has been considered as an important candidate of light elements in the Earth's core. Because iron hydrides are unquenchable, hydrogen content is usually estimated from in situ X-ray diffraction measurements that assume the following linear relation: x = (V-FeHx - V-Fe)/Delta V-H, where x is the hydrogen content, Delta V-H is the volume expansion caused by unit concentration of hydrogen, and V-FeHx and V-Fe are volumes of FeHx and pure iron, respectively. To verify the linear relationship, we computed the equation of states of hexagonal iron with interstitial hydrogen by using the Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA). The results indicate a discontinuous volume change at the magnetic transition and almost no compositional (x) dependence in the ferromagnetic phase at 20 GPa, whereas the linearity is confirmed in the non-magnetic phase. In addition to their effect on the density-composition relationship in the Fe-FeHx system, which is important for estimating the hydrogen incorporation in planetary cores, the magnetism and interstitial hydrogen also affect the electrical resistivity of FeHx. The thermal conductivity can be calculated from the electrical resistivity by using the Wiedemann-Franz law, which is a critical parameter for modeling the thermal evolution of the Earth. Assuming an Fe1-ySiyHx ternary outer core model (0.0 <= x <= 0.7), we calculated the thermal conductivity and the age of the inner core. The resultant thermal conductivity is similar to 100 W/m/K and the maximum inner core age ranges from 0.49 to 0.86 Gyr. No potential conflict of interest relevant to this article was reported.

FRONTIERS MEDIA SA Acta Medica Okayama 2296-6463 6 2018 Impurity Resistivity of fcc and hcp Fe-Based Alloys: Thermal Stratification at the Top of the Core of Super-Earths 217 EN Hitoshi Gomi Institute for Planetary Materials, Okayama University Takashi Yoshino Institute for Planetary Materials, Okayama University It is widely known that the Earth's Fe dominant core contains a certain amount of light elements such as H, C, N, O, Si, and S. We report the results of first-principles calculations on the band structure and the impurity resistivity of substitutionally disordered hcp and fcc Fe based alloys. The calculation was conducted by using the AkaiKKR (machikaneyama) package, which employed the Korringa-Kohn-Rostoker (KKR) method with the atomic sphere approximation (ASA). The local density approximation (LDA) was adopted for the exchange-correlation potential. The coherent potential approximation (CPA) was used to treat substitutional disorder effect. The impurity resistivity is calculated from the Kubo-Greenwood formula with the vertex correction. In dilute alloys with 1 at. % impurity concentration, calculated impurity resistivities of C, N, O, S are comparable to that of Si. On the other hand, in concentrated alloys up to 30 at. %, Si impurity resistivity is the highest followed by C impurity resistivity. Ni impurity resistivity is the smallest. N, O, and S impurity resistivities lie between Si and Ni. Impurity resistivities of hcp-based alloys show systematically higher values than fcc alloys. We also calculated the electronic specific heat from the density of states (DOS). For pure Fe, the results show the deviation from the Sommerfeld value at high temperature, which is consistent with previous calculation. However, the degree of deviation becomes smaller with increasing impurity concentration. The violation of the Sommerfeld expansion is one of the possible sources of the violation of the Wiedemann-Franz law, but the present results could not resolve the inconsistency between recent electrical resistivity and thermal conductivity measurements. Based on the present thermal conductivity model, we calculated the conductive heat flux at the top of terrestrial cores, which is comparable to the heat flux across the thermal boundary layer at the bottom of the mantle. This indicates that the thermal stratification may develop at the top of the liquid core of super-Earths, and hence, chemical buoyancies associated with the inner core growth and/or precipitations are required to generate the global magnetic field through the geodynamo. No potential conflict of interest relevant to this article was reported.