In the search of promising Na-ion cathode materials, high-pressure synthesis method was applied t... more In the search of promising Na-ion cathode materials, high-pressure synthesis method was applied to obtain sodium iron fluoride NaFeF 3 with the post-perovskite lamellar structure. A two-step synthesis was performed: first, the Pnma orthorhombic perovskite structure NaFeF 3 form (or Pv-NaFeF 3 , GdFeO 3 type) was synthesized at 1270 K and 7.7 GPa, then the Cmcm orthorhombic post-perovskite structure (or pPv-NaFeF 3 , CaIrO 3 type) was obtained using a second step at 700 K and 15 GPa. The post-perovskite form was stabilized under ambient conditions with a low amount of remaining perovskite phase (5 mol%). The M€ ossbauer analysis of pPv-NaFeF 3 was firstly investigated with a paramagnetic structure obtained at 300 and 77 K, opposed to Pv-NaFeF 3 magnetism reflecting the different [FeF 6 ] polyhedra arrangements. Finally, the sodium migration within the framework of both structures was evaluated with the use of Bond Valence Energy Landscape (BVEL) calculations, resulting with an enhanced Na þ mobility within the pPv-NaFeF 3 structure.
Physics of the Earth and Planetary Interiors, 2021
High-pressure and hightemperature phase relations in the systems KAlSiO4-MgAl2O4 and CaAl2O4-MgAl... more High-pressure and hightemperature phase relations in the systems KAlSiO4-MgAl2O4 and CaAl2O4-MgAl2O4: Stability fields of NAL phases,
High-pressure phase relations in the system NaAl3Si3O11–CaAl4Si2O11 were examined at 13–23GPa and... more High-pressure phase relations in the system NaAl3Si3O11–CaAl4Si2O11 were examined at 13–23GPa and 1600–1900°C, using a multianvil apparatus. A Ca-aluminosilicate with CaAl4Si2O11 composition, designated CAS phase, is stable above about 13GPa at 1600°C. In the system NaAl3Si3O11–CaAl4Si2O11, the CAS phase dissolving NaAl3Si3O11 component coexists with jadeite, corundum and stishovite below 22GPa, above which the CAS phase coexists with Na-rich calcium ferrite,
BaIrO 3 adopts the 9R polytype structure if it is synthesized at ambient pressure. High-pressure ... more BaIrO 3 adopts the 9R polytype structure if it is synthesized at ambient pressure. High-pressure and hightemperature treatments up to 10 GPa have led to other 5H and 6H polytype phases, which are quenchable to the ambient condition. However, the single-phase 3C perovskite, the end member of polytypes, has not been obtained so far. Here we report the high-pressure synthesis of BaIrO 3 perovskite under 25 GPa and 1150 • C. Rietveld refinement on the powder x-ray diffraction pattern revealed that this new compound crystallizes in a tetragonal I 4/mcm structure rather than the expected cubic Pm-3m structure. The new perovskite is a Pauli paramagnetic metal with a Fermi liquid ground state, i.e., ρ ∝ T 2 below 6 K. The availability of BaIrO 3 perovskite also allows completion of the structure-physical property evolution in the AIrO 3 perovskites (A = Ca, Sr, Ba). The Fermi energy located in bands originated from Ir: 5d and O: 2p electrons are found to be very sensitive to the change of crystal structure.
This session aims at discussing various dynamic phenomena in the Earth's deep interior, such as t... more This session aims at discussing various dynamic phenomena in the Earth's deep interior, such as the interactions among the plates, mantle and core. Presentations of theoretical experimental/observational studies on high-pressure physics, seismology, and mantle/core dynamics are widely accepted.
The Review of High Pressure Science and Technology, 2016
In this article, advances on phase-transition studies of mantle minerals in the Earth's interior ... more In this article, advances on phase-transition studies of mantle minerals in the Earth's interior are reviewed. Precise phase relations of minerals and related inorganic compounds at high pressure have been determined by precise high-pressure experiments and also by thermodynamic calculations based on calorimetric measurements. Crystal-chemical studies on high-pressure analogue compounds for silicates and aluminates have been made to get insight to crystal structures and properties of the minerals stable in the deep Earth's interior. The results substantially advance our understanding of the structure and dynamics of the deep mantle. [phase transition, thermodynamics, multianvil, calorimetry, crystal chemistry, mantle mineral, analogue compound, transition zone, lower mantle] . はじめに
In high-pressure high-temperature conditions in the earth's interior, constituent minerals of the... more In high-pressure high-temperature conditions in the earth's interior, constituent minerals of the mantle transform to denser phases. The most abundant mineral, (Mg, Fe)2SiO4 olivine, transforms to high-pressure phases with spinel structure and (Mg, Fe)SiO3 perovskite plus rocksaltstructured (Mg, Fe)O at the depths where seismic velocities suddenly increase. The equilibrium transition boundaries for the high-pressure transitions of olivine have been accurately determined by high-pressure high-temperature experiments and thermodynamic calculation based on calorimetric data. The results have been used to estimate temperature distribution in the mantle. High-pressure phase relations of pyroxenes and garnet have also been determined by high-pressure experiments and thermodynamic calculation. Combining the phase relations of the mantle minerals, constitution of the deep earth has been mostly clarified. Recent progress in high-pressure experiments has strongly suggested that Mg-rich perovskite further transforms to a denser structure near the base of the mantle.
Phase transitions of Mg 2 TiO 4 and Fe 2 TiO 4 were examined up to 28 GPa and 1600 • C using a mu... more Phase transitions of Mg 2 TiO 4 and Fe 2 TiO 4 were examined up to 28 GPa and 1600 • C using a multianvil apparatus. The quenched samples were examined by powder X-ray diffraction. With increasing pressure at high temperature, spinel-type Mg 2 TiO 4 decomposes into MgO and ilmenite-type MgTiO 3 which further transforms to perovskite-type MgTiO 3. At~21 GPa, the assemblage of MgTiO 3 perovskite + MgO changes to 2MgO + TiO 2 with baddeleyite (or orthorhombic I)-type structure. Fe 2 TiO 4 undergoes transitions similar to Mg 2 TiO 4 with pressure: spinel-type Fe 2 TiO 4 dissociates into FeO and ilmenite-type FeTiO 3 which transforms to perovskite-type FeTiO 3. Both of MgTiO 3 and FeTiO 3 perovskites change to LiNbO 3-type phases on release of pressure. In Fe 2 TiO 4 , however, perovskite-type FeTiO 3 and FeO combine into calcium titanate-type Fe 2 TiO 4 at~15 GPa. The formation of calcium titanate-type Fe 2 TiO 4 at high pressure may be explained by effects of crystal field stabilization and high spin-low spin transition in Fe 2+ in the octahedral sites of calcium titanate-type Fe 2 TiO 4. It is inferred from the determined phase relations that some of Fe 2 TiO 4-rich titanomagnetite inclusions in diamonds recently found in São Luiz, Juina, Brazil, may be originally calcium titanate-type Fe 2 TiO 4 at pressure above~15 GPa in the transition zone or lower mantle and transformed to spinel-type in the upper mantle conditions.
The Al-Si-V system is assessed to understand the phase equilibria of V-containing (3d transition ... more The Al-Si-V system is assessed to understand the phase equilibria of V-containing (3d transition metal) Al-Si alloys, which are generally of great importance for technical applications. Four annealed alloys were prepared to study the phase equilibria of Al-rich corner (V ≤ 23.3 at.%, Si ≤ 57.6 at.%) in the temperature range of 500-930 • C. The microstructure and phase constituents of the samples were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS). The existence of ternary phase (Al 0.6 Si 1.4 V, TiSi 2-type) was confirmed with the composition ranging from 17.98 to 18.59 at.% Al and 48.89-49.20 at.% Si. However, it did not equilibrate with fcc(Al) below 868 • C, which was determined by differential scanning calorimetry (DSC). The Si 3 V 5 appeared in Al 58.5 Si 18.3 V 23.2 and Al 64.7 Si 20.2 V 15.1 alloys annealed at 500 • C. It nearly disappeared after 3000 h-annealing and its thermodynamic stability was discussed. According to the measured phase relationships, the thermodynamic description of Al-Si-V system was optimized combing with the enthalpies of formation of binary and ternary compounds obtained by density functional theory (DFT). The Si-V system was modified to obtain the congruent liquidus of Si 3 V 5 and enthalpy of formation of Si 3 V 5 and Si 2 V with experimental data. By comparing the calculated phase equilibria and phase transitions with experimental data, it showed that a good agreement was reached. The description of Al-Si-V system could be used to guide the development of Al-Si alloys.
We investigated the doping effects of magnetic and nonmagnetic impurities on the singlecrystallin... more We investigated the doping effects of magnetic and nonmagnetic impurities on the singlecrystalline p-type Ba0.5K0.5Fe2−2xM 2xAs2 (M = Mn, Ru, Co, Ni, Cu and Zn) superconductors. The superconductivity indicates robustly against impurity of Ru, while weakly against the impurities of Mn, Co, Ni, Cu, and Zn. However, the present T c suppression rate of both magnetic and and nonmagnetic impurities remains much lower than what was expected for the s±-wave model. The temperature dependence of resistivity data is observed an obvious low-T upturn for the crystals doped with high-level impurity, which is due to the occurrence of localization. Thus, the relatively weak T c suppression effect from Mn, Co, Ni, Cu, and Zn are considered as a result of localization rather than pair-breaking effect in s±-wave model.
Zenodo (CERN European Organization for Nuclear Research), Nov 7, 2019
Data set for Discovery of new-structured post-spinel MgFe2O4: Crystal structure and high-pressure... more Data set for Discovery of new-structured post-spinel MgFe2O4: Crystal structure and high-pressure phase relations.
In the search of promising Na-ion cathode materials, high-pressure synthesis method was applied t... more In the search of promising Na-ion cathode materials, high-pressure synthesis method was applied to obtain sodium iron fluoride NaFeF 3 with the post-perovskite lamellar structure. A two-step synthesis was performed: first, the Pnma orthorhombic perovskite structure NaFeF 3 form (or Pv-NaFeF 3 , GdFeO 3 type) was synthesized at 1270 K and 7.7 GPa, then the Cmcm orthorhombic post-perovskite structure (or pPv-NaFeF 3 , CaIrO 3 type) was obtained using a second step at 700 K and 15 GPa. The post-perovskite form was stabilized under ambient conditions with a low amount of remaining perovskite phase (5 mol%). The M€ ossbauer analysis of pPv-NaFeF 3 was firstly investigated with a paramagnetic structure obtained at 300 and 77 K, opposed to Pv-NaFeF 3 magnetism reflecting the different [FeF 6 ] polyhedra arrangements. Finally, the sodium migration within the framework of both structures was evaluated with the use of Bond Valence Energy Landscape (BVEL) calculations, resulting with an enhanced Na þ mobility within the pPv-NaFeF 3 structure.
Physics of the Earth and Planetary Interiors, 2021
High-pressure and hightemperature phase relations in the systems KAlSiO4-MgAl2O4 and CaAl2O4-MgAl... more High-pressure and hightemperature phase relations in the systems KAlSiO4-MgAl2O4 and CaAl2O4-MgAl2O4: Stability fields of NAL phases,
High-pressure phase relations in the system NaAl3Si3O11–CaAl4Si2O11 were examined at 13–23GPa and... more High-pressure phase relations in the system NaAl3Si3O11–CaAl4Si2O11 were examined at 13–23GPa and 1600–1900°C, using a multianvil apparatus. A Ca-aluminosilicate with CaAl4Si2O11 composition, designated CAS phase, is stable above about 13GPa at 1600°C. In the system NaAl3Si3O11–CaAl4Si2O11, the CAS phase dissolving NaAl3Si3O11 component coexists with jadeite, corundum and stishovite below 22GPa, above which the CAS phase coexists with Na-rich calcium ferrite,
BaIrO 3 adopts the 9R polytype structure if it is synthesized at ambient pressure. High-pressure ... more BaIrO 3 adopts the 9R polytype structure if it is synthesized at ambient pressure. High-pressure and hightemperature treatments up to 10 GPa have led to other 5H and 6H polytype phases, which are quenchable to the ambient condition. However, the single-phase 3C perovskite, the end member of polytypes, has not been obtained so far. Here we report the high-pressure synthesis of BaIrO 3 perovskite under 25 GPa and 1150 • C. Rietveld refinement on the powder x-ray diffraction pattern revealed that this new compound crystallizes in a tetragonal I 4/mcm structure rather than the expected cubic Pm-3m structure. The new perovskite is a Pauli paramagnetic metal with a Fermi liquid ground state, i.e., ρ ∝ T 2 below 6 K. The availability of BaIrO 3 perovskite also allows completion of the structure-physical property evolution in the AIrO 3 perovskites (A = Ca, Sr, Ba). The Fermi energy located in bands originated from Ir: 5d and O: 2p electrons are found to be very sensitive to the change of crystal structure.
This session aims at discussing various dynamic phenomena in the Earth's deep interior, such as t... more This session aims at discussing various dynamic phenomena in the Earth's deep interior, such as the interactions among the plates, mantle and core. Presentations of theoretical experimental/observational studies on high-pressure physics, seismology, and mantle/core dynamics are widely accepted.
The Review of High Pressure Science and Technology, 2016
In this article, advances on phase-transition studies of mantle minerals in the Earth's interior ... more In this article, advances on phase-transition studies of mantle minerals in the Earth's interior are reviewed. Precise phase relations of minerals and related inorganic compounds at high pressure have been determined by precise high-pressure experiments and also by thermodynamic calculations based on calorimetric measurements. Crystal-chemical studies on high-pressure analogue compounds for silicates and aluminates have been made to get insight to crystal structures and properties of the minerals stable in the deep Earth's interior. The results substantially advance our understanding of the structure and dynamics of the deep mantle. [phase transition, thermodynamics, multianvil, calorimetry, crystal chemistry, mantle mineral, analogue compound, transition zone, lower mantle] . はじめに
In high-pressure high-temperature conditions in the earth's interior, constituent minerals of the... more In high-pressure high-temperature conditions in the earth's interior, constituent minerals of the mantle transform to denser phases. The most abundant mineral, (Mg, Fe)2SiO4 olivine, transforms to high-pressure phases with spinel structure and (Mg, Fe)SiO3 perovskite plus rocksaltstructured (Mg, Fe)O at the depths where seismic velocities suddenly increase. The equilibrium transition boundaries for the high-pressure transitions of olivine have been accurately determined by high-pressure high-temperature experiments and thermodynamic calculation based on calorimetric data. The results have been used to estimate temperature distribution in the mantle. High-pressure phase relations of pyroxenes and garnet have also been determined by high-pressure experiments and thermodynamic calculation. Combining the phase relations of the mantle minerals, constitution of the deep earth has been mostly clarified. Recent progress in high-pressure experiments has strongly suggested that Mg-rich perovskite further transforms to a denser structure near the base of the mantle.
Phase transitions of Mg 2 TiO 4 and Fe 2 TiO 4 were examined up to 28 GPa and 1600 • C using a mu... more Phase transitions of Mg 2 TiO 4 and Fe 2 TiO 4 were examined up to 28 GPa and 1600 • C using a multianvil apparatus. The quenched samples were examined by powder X-ray diffraction. With increasing pressure at high temperature, spinel-type Mg 2 TiO 4 decomposes into MgO and ilmenite-type MgTiO 3 which further transforms to perovskite-type MgTiO 3. At~21 GPa, the assemblage of MgTiO 3 perovskite + MgO changes to 2MgO + TiO 2 with baddeleyite (or orthorhombic I)-type structure. Fe 2 TiO 4 undergoes transitions similar to Mg 2 TiO 4 with pressure: spinel-type Fe 2 TiO 4 dissociates into FeO and ilmenite-type FeTiO 3 which transforms to perovskite-type FeTiO 3. Both of MgTiO 3 and FeTiO 3 perovskites change to LiNbO 3-type phases on release of pressure. In Fe 2 TiO 4 , however, perovskite-type FeTiO 3 and FeO combine into calcium titanate-type Fe 2 TiO 4 at~15 GPa. The formation of calcium titanate-type Fe 2 TiO 4 at high pressure may be explained by effects of crystal field stabilization and high spin-low spin transition in Fe 2+ in the octahedral sites of calcium titanate-type Fe 2 TiO 4. It is inferred from the determined phase relations that some of Fe 2 TiO 4-rich titanomagnetite inclusions in diamonds recently found in São Luiz, Juina, Brazil, may be originally calcium titanate-type Fe 2 TiO 4 at pressure above~15 GPa in the transition zone or lower mantle and transformed to spinel-type in the upper mantle conditions.
The Al-Si-V system is assessed to understand the phase equilibria of V-containing (3d transition ... more The Al-Si-V system is assessed to understand the phase equilibria of V-containing (3d transition metal) Al-Si alloys, which are generally of great importance for technical applications. Four annealed alloys were prepared to study the phase equilibria of Al-rich corner (V ≤ 23.3 at.%, Si ≤ 57.6 at.%) in the temperature range of 500-930 • C. The microstructure and phase constituents of the samples were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS). The existence of ternary phase (Al 0.6 Si 1.4 V, TiSi 2-type) was confirmed with the composition ranging from 17.98 to 18.59 at.% Al and 48.89-49.20 at.% Si. However, it did not equilibrate with fcc(Al) below 868 • C, which was determined by differential scanning calorimetry (DSC). The Si 3 V 5 appeared in Al 58.5 Si 18.3 V 23.2 and Al 64.7 Si 20.2 V 15.1 alloys annealed at 500 • C. It nearly disappeared after 3000 h-annealing and its thermodynamic stability was discussed. According to the measured phase relationships, the thermodynamic description of Al-Si-V system was optimized combing with the enthalpies of formation of binary and ternary compounds obtained by density functional theory (DFT). The Si-V system was modified to obtain the congruent liquidus of Si 3 V 5 and enthalpy of formation of Si 3 V 5 and Si 2 V with experimental data. By comparing the calculated phase equilibria and phase transitions with experimental data, it showed that a good agreement was reached. The description of Al-Si-V system could be used to guide the development of Al-Si alloys.
We investigated the doping effects of magnetic and nonmagnetic impurities on the singlecrystallin... more We investigated the doping effects of magnetic and nonmagnetic impurities on the singlecrystalline p-type Ba0.5K0.5Fe2−2xM 2xAs2 (M = Mn, Ru, Co, Ni, Cu and Zn) superconductors. The superconductivity indicates robustly against impurity of Ru, while weakly against the impurities of Mn, Co, Ni, Cu, and Zn. However, the present T c suppression rate of both magnetic and and nonmagnetic impurities remains much lower than what was expected for the s±-wave model. The temperature dependence of resistivity data is observed an obvious low-T upturn for the crystals doped with high-level impurity, which is due to the occurrence of localization. Thus, the relatively weak T c suppression effect from Mn, Co, Ni, Cu, and Zn are considered as a result of localization rather than pair-breaking effect in s±-wave model.
Zenodo (CERN European Organization for Nuclear Research), Nov 7, 2019
Data set for Discovery of new-structured post-spinel MgFe2O4: Crystal structure and high-pressure... more Data set for Discovery of new-structured post-spinel MgFe2O4: Crystal structure and high-pressure phase relations.
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Papers by Masaki Akaogi