A5084430946- High-pressure geophysics and materials
- Rare-earth and actinide compounds
- X-ray Diffraction in Crystallography
- Diamond and Carbon-based Materials Research
- Advanced Condensed Matter Physics
- Crystal Structures and Properties
- Boron and Carbon Nanomaterials Research
- Physics of Superconductivity and Magnetism
- Crystallization and Solubility Studies
- Ferroelectric and Piezoelectric Materials
- Solid-state spectroscopy and crystallography
- Iron-based superconductors research
- Nuclear Materials and Properties
- Superconductivity in MgB2 and Alloys
- Microwave Dielectric Ceramics Synthesis
- Magnetic Properties and Synthesis of Ferrites
- Hydrogen Storage and Materials
- Magnetic and transport properties of perovskites and related materials
- Luminescence Properties of Advanced Materials
- Liquid Crystal Research Advancements
- Superconducting Materials and Applications
- Orbital Angular Momentum in Optics
- Advanced Chemical Physics Studies
- Metal and Thin Film Mechanics
- Advanced ceramic materials synthesis
Osaka University
2013-2024
Jilin Medical University
2022
Jilin University
2022
Nagaoka University of Technology
2017-2019
Osaka Kyoiku University
2005-2019
Kindai University Sakai Hospital
2018
Nagaoka University
2017
University of the Ryukyus University Hospital
2015
Carnegie Institution for Science
2005-2015
Geophysical Laboratory
2005-2015
A sharp focus of current research on superconducting superhydrides is to raise their critical temperature Tc at moderate pressures. Here, we report a discovery giant enhancement in CeH9 obtained via random substitution half Ce by La, leading equal-atomic (La,Ce)H9 alloy stabilized maximum configurational entropy, containing the LaH9 unit that unstable pure compound form. The synthesized exhibits 148-178 K pressure range 97-172 GPa, representing up 80% compared and showcasing highest...
Polyhydrides are a novel class of superconducting materials with extremely high critical parameters, which is very promising for sensor applications. On the other hand, complete experimental study best so far known superconductor, lanthanum superhydride LaH10 , encounters serious complication because large upper magnetic field HC2 (0), exceeding 120-160 T. It found that partial replacement La atoms by Nd results in significant suppression superconductivity : each at% causes decrease TC 10-11...
The pressure dependence of the superconducting transition temperature T c in calcium was measured up to 161 GPa. increased significantly with and reached 25 K at GPa, which is highest observed for all elements. Compared result obtained a recent structural experiment, increases within simple cubic structure phase becomes rather stable but still Ca-IV Ca-V phases.
Pressure-induced superconductivity and structural phase transitions in calcium (Ca) were studied by electrical resistance measurements angular dispersive x-ray diffraction under pressures above 200 GPa. Other alkaline-earth metals, Sr Ba, have a high-pressure with ``host-guest'' structure, the maximum superconducting transition temperature ${T}_{\mathrm{c}}$ is observed this phase. However, host-guest structure has not yet been Ca. In work, we found (Ca-VII) around 210 GPa structure....
Three structures of CaMn2O4, CaFe2O4, and CaTi2O4 have been proposed as post-spinel phases. Because these are very similar, several ambiguities inconsistencies appear in high-pressure studies, leading to many problems that yet be solved. Systematic powder diffraction studies related three phases were conducted under high pressure using synchrotron radiation. All samples further polymorphs. CaMn2O4 transforms the CaTi2O4-type structure at about 30 GPa. The MnO6 octahedron lower-pressure is...
We report the metal (0--80 GPa)--semiconductor ($oC$40, 80--120 GPa)--metal ($oC$24, >120 GPa) transitions of lithium under compression, as observed through simultaneous electrical resistance and x-ray diffraction measurements. The energy gap in $oC$40 semiconductor quickly decreases with applied pressure, Li reverts back to a metallic state accompanied by structural transition $oC$24. large $\ensuremath{\rho}$ value for $oC$24 indicates that this re-entrant phase is so-called ``poor...
An angular dispersive X-ray diffraction experiment on calcium metal (Ca) has been performed at high pressures up to 139 GPa. Ca forms a face-centered cubic (fcc) lattice ambient conditions, transforms body-centered (bcc) 20 GPa, and further simple structure 32 We found the phase in wide pressure range, from about 109 discovered new high-pressure above 113
Abstract The pressure dependence of the superconducting transition temperature ( T c ) and unit cell metrics tetragonal (NH 3 y Cs 0.4 FeSe were investigated in high pressures up to 41 GPa. decreases with increasing 13 GPa, which can be clearly correlated (or layer spacing). vs . plot is compared those various M x (M: metal atoms) materials exhibiting different , showing that universally related This behaviour means a decrease two-dimensionality lowers No superconductivity was observed down...
Abstract A new method for synthesis of metal polyhydrides via high‐pressure thermal decomposition corresponding amidoboranes in diamond anvil cells is proposed. Within this approach, molecular semiconducting cesium ( P 4/ nmm ‐CsH 7 , 1‐CsH 15+x ) and rubidium (RbH 9‐x with a very high hydrogen content reaching 93 at.% are synthesized. Preservation CsH at near ambient conditions, confirmed both experimentally theoretically, represents significant advance the stabilization hydrogen‐rich...
Compressed calcium exhibits successive structural transitions: face-centered cubic $(\text{Ca-I})\ensuremath{\rightarrow}\text{body}\text{\ensuremath{-}}\text{centered}$ $(\text{Ca-II})\ensuremath{\rightarrow}\text{simple}$ $(\text{Ca-III})\ensuremath{\rightarrow}P{4}_{1}{2}_{1}2$ $(\text{Ca-IV})\ensuremath{\rightarrow}Cmca$ (Ca-V). We performed x-ray diffraction measurements of at pressure up to 172 GPa room temperature and noted a high-pressure phase ``Ca-VI'' above 158 GPa. The structure...
The recently discovered high pressure phase VII of calcium [M. Sakata et al., Phys. Rev. B 83, 220512(R) (2011)] has the highest superconducting transition temperature (T(c)) 29 K among all elements. Understanding cause for such a T(c) state is necessary to clarify its crystal structure. structure this was determined by an x-ray powder diffraction experiment and density functional theory calculation not found be usual host-guest type but consisted 2×2 supercell in tetragonal ab plane with...
The Jahn-Teller effect at Cu2+ in cuprospinel CuFe2O4 was investigated using high-pressure single-crystal synchrotron X‑ray diffraction techniques beamline BL10A the Photon Factory, KEK, Japan. Six data sets were collected pressure range from ambient to 5.9 GPa room temperature. Structural refinements based on performed 0.0, 1.8, 2.7, and 4.6 GPa. unit-cell volume of decreases continuously 590.8(6) 579.5(8) Å3 up 3.8 Least-squares fitting a third-order Birch-Murnaghan equation state yields...
High-pressure phases IV and V of calcium discovered in 2005 have the highest superconducting transition temperature 25 K among all elements; however, their crystal structures not been determined. From x-ray powder diffraction data, both Ca found to form unique complex with a coordination number 7. They were confirmed be identical theoretical models that recently predicted [Ishikawa et al., Phys. Rev. B 77 020101(R) (2008)].
The effect of pressure on the crystal structure ${\mathrm{Ni}}_{2}\mathrm{MnGa}$ was investigated up to 41 GPa using in situ angle-dispersive x-ray diffraction with synchrotron radiation, an imaging plate detector, and a diamond anvil cell. A pressure-induced transition from cubic $L{2}_{1}$ (space group $\mathit{Fm}\overline{3} m$) 10-layer modulated monoclinic ($C2/m$) distortion $\ensuremath{\beta}\ensuremath{\sim}{92}^{\ensuremath{\circ}}$ occurred at 19.1 or lower. volume change...
Nano-polycrystalline diamonds (NPDs) consist of nanosized diamond grains oriented in random directions. They have high toughness and isotropic mechanical properties. A NPD has neither the cleavage feature nor anisotropy hardness peculiar to single-crystal diamonds. Therefore, it is thought be useful as a anvil. We previously reported usefulness an anvil for high-pressure development. In this study, some additional generating tests using anvils various shapes prepared from NPDs were conducted...
High-pressure powder x-ray diffraction experiments have been carried out on solid mercury up to 196 GPa at room temperature. The hexagonal-close-packed δ phase, which exists above 36 GPa, is found remain stable the highest pressure investigated. c/a axial ratio monotonously decreases under in a manner similar that of zinc and cadmium. There no anomaly dependence ratio. We present complete structural data β, γ, phases mercury, constrain PV equation state 300 K.
The structural phase transition of the titanomagnetite (Fe3-xTixO4) solid solution under pressures up to 60 GPa has been clarified by single-crystal and powder diffraction studies using synchrotron radiation a diamond-anvil cell. Present Rietveld structure refinements prove that prefered cation distribution is based on crystal field preference rather than magnetic spin ordering in solution.
A nano-polycrystalline diamond was synthesized from graphite by direct conversion under high pressure. The consists of nanosized grains oriented in random directions and has higher toughness more isotropic mechanical properties than the single-crystal diamond. We generated pressure using a pair anvils composed particles. highest achieved 210 GPa. maximum almost same as that anvils.
Jahn-Teller transition of ulv\"ospinel ${\text{Fe}}_{2}{\text{TiO}}_{4}$ has been investigated by single-crystal x-ray diffraction study under high pressures up to 15 GPa at ambient temperature using synchrotron radiation and the low-temperature condition down $\ensuremath{-}170\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ pressure. The from cubic tetragonal is induced distortion due effect ${\text{Fe}}^{2+}$ tetrahedral site. phase takes place 9 with increasing pressure $20\text{ was...
The electron-density distribution of single-crystal ${\text{KNbO}}_{3}$ has been measured as a function pressure using synchrotron-radiation techniques in order to understand the variation its static dielectric properties. adopts three different polymorphs at varying pressures and ambient temperature: phase an orthorhombic $Cm2m$ $(Amm2)$ structure that transforms tetragonal $(P4mm)$ about 7.0 GPa, which then further cubic $Pm3m$ 10.0 GPa. is paraelectric, while two lower-pressure phases are...
Quantum spin liquid states have garnered significant attention as potential precursors for high-temperature superconductors. Researchers are aiming to achieve superconductivity through regulation. However, previous studies indicated that candidate materials with honeycomb structures, such $\mathrm{N}{\mathrm{a}}_{2}\mathrm{Ir}{\mathrm{O}}_{3}$ and $\ensuremath{\alpha}\ensuremath{-}\mathrm{L}{\mathrm{i}}_{2}\mathrm{Ir}{\mathrm{O}}_{3}$, remain in a magnetically ordered insulating state....
The superconductivity and structural properties of lithium under high pressure are investigated by simultaneous measurements X-ray diffraction electrical resistance at low temperature below 25 K. transitions fcc - hR1 cI16 near 40 GPa the possible transition to higher phases were observed above 70 GPa. superconducting Tc increases with applied has maximum in phase. At pressures, decreases phase again We did not observe 9 K for pressures Superconductivity possibly disappears
Abstract Polyhydrides are a novel class of superconducting materials with extremely high critical parameters, which is very promising for applications. On the other hand, complete experimental study magnetic phase diagram best so far known superconductor, lanthanum decahydride LaH 10 , encounters serious complication because large upper field H C2 (0), exceeding 120–160 T. Partial replacement La atoms by Nd results in decrease field, makes it attainable existing pulse magnets. We found that...