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121 results on '"Hirai, Shigeto"'

2. Fluorine solubility and superconducting properties of Sm(O,F)BiS$_2$ single crystals

Author

Kinami, Koki, Hanada, Yuji, Nagao, Masanori, Miura, Akira, Hirai, Shigeto, Maruyama, Yuki, Watauchi, Satoshi, and Tanaka, Isao

Subjects
Condensed Matter - Superconductivity
Abstract

Sm(O,F)BiS2 superconducting single crystals with various nominal F contents have been grown using KI-KCl flux. The solid solution limit of F at the O-site in Sm(O,F)BiS2 single crystals was approximately less than 20 at%. F concentrations of Sm(O,F)BiS2 single crystals were hardly controlled by nominal F contents. It suggests the existence of intrinsic stable phase. Superconductivity was shown at around 5 K. Superconducting transition temperature with zero resistivity were increased with increasing nominal F contents within less than 70 at% in O-site, despite similar F concentration and c-axis lattice constants.

Published
2021
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5. Superconducting transition temperatures in the electronic and magnetic phase diagrams of Sr2VFeAsO3-delta, a superconductor

Author

Tojo, Yujiro, Shibuya, Taizo, Nakamura, Tetsuro, Shoji, Koichiro, Fujioka, Hirotaka, Matoba, Masanori, Yasui, Shintaro, Itoh, Mitsuru, Iimura, Soshi, Hiramatsu, Hidenori, Hosono, Hideo, Hirai, Shigeto, Mao, Wendy, Kitao, Shinji, Seto, Makoto, and Kamihara, Yoichi

Subjects
Condensed Matter - Superconductivity
Abstract

We elucidate the magnetic phases and superconducting transition temperatures (Tc) in Sr2VFeAsO3-delta (21113V), an iron-based superconductor with a thick-blocking layer fabricated from a perovskite-related transition metal oxide. At low temperatures (T < 37.1 K), 21113V exhibited a superconducting phase in the range 0.031 =< delta =< 0.145 and an antiferromagnetic (AFM) iron sublattice in the range 0.267 =< delta =< 0.664. Mixed-valent vanadium exhibited a dominant AFM phase in 0.031 =< delta =< 0.088, and a partial ferrimagnetic (Ferri.) phase in the range 0.124 =< delta =< 0.664. The Ferri. phase was the most dominant at a delta value of 0.267, showing an AFM phase of Fe at T < 20 K. Increasing the spontaneous magnetic moments reduced the magnetic shielding volume fraction due to the superconducting phase. This result was attributed to the magnetic phase of vanadium, which dominates the superconductivity of Fe in 21113V. The Tc-delta curve showed two maxima. The smaller and larger of Tc maxima occurred at delta = 0.073 and delta = 0.145, respectively; the latter resides on the phase boundary between AFM and the partial Ferri. phases of vanadium. 21113V is a useful platform for verifing new mechanisms of Tc enhancement in iron-based superconductors., Comment: 34 pages, 10 figures, 2 tables, supplement information with 11 pages, 8 figures, 3 tables. accepted for publication, J. Phys.: Condens. Matter, Updated manuscript contains More references and readability. See http://iopscience.iop.org/article/10.1088/1361-648X/aaf7e0

Published
2018
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8. Giant atomic displacement induced by built-in strain in metastable Mn$_3$O$_4$

Author

Hirai, Shigeto, Santos, Antonio M. dos, Shapiro, Maxwell C., Molaison, Jamie J., Pradhan, Neelam, Guthrie, Malcolm, Tulk, Christopher A., Fisher, Ian R., and Mao, Wendy L.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We present x-ray, neutron scattering and heat capacity data that reveal a coupled first-order magnetic and structural phase transition of the metastable mixed-valence post-spinel compound Mn$_3$O$_4$ at 210 K. Powder neutron diffraction measurements reveal a magnetic structure in which Mn$^{3+}$ spins align antiferromagnetically along the edge-sharing \emph{a}-axis, with a magnetic propagation vector k = [1/2, 0, 0]. In contrast, the Mn$^{2+}$ spins, which are geometrically frustrated, do not order until a much lower temperature. Although the Mn$^{2+}$ spins do not directly participate in the magnetic phase transition at 210 K, structural refinements reveal a large atomic shift at this phase transition, corresponding to a physical motion of approximately 0.25 {\AA} even though the crystal symmetry remains unchanged. This "giant" response is due to the coupled effect of built-in strain in the metastable post-spinel structure with the orbital realignment of the Mn$^{3+}$ ion., Comment: Main text plus supplemental material

Published
2012

9. Pressure-induced symmetry breaking in tetragonal CsAuI3

Author

Wang, Shibing, Hirai, Shigeto, Shapiro, Maxwell C., Riggs, Scott C., Geballe, Theodore H., Mao, Wendy L., and Fisher, Ian R.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science
Abstract

Results of in situ high pressure x-ray powder diffraction on the mixed valence compound Cs2Au(I)Au(III)I6 (CsAuI3) are reported, for pressures up to 21 GPa in a diamond anvil cell under hydrostatic conditions. We find a reversible pressure-induced tetragonal to orthorhombic structural transition at 5.5-6 GPa, and reversible amorphization at 12-14 GPa. Two alternative structures are proposed for the high-pressure orthorhombic phase, and are discussed in the context of a possible Au valence transition., Comment: 7 figures

Published
2012
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12. Investigation of CaIr1-xPtxO3 and CaIr0.5Rh0.5O3 : structural properties, physical properties and stabilising conditions for post-perovskite oxides

Author

Hirai, Shigeto, Attfield, J. Paul, Bromiley, Geoffrey., Klemme, Stephan., and Harley, Simon

Subjects
550, post-perovskite, hard magnet, ODF, Orientation Density Function, CaIrO3
Abstract

Our understanding of the nature of Earth’s D” region was changed significantly by a recent finding by Murakami et al. (2004), who revealed a phase transition from perovskite to post-perovskite structure in MgSiO3 at about 125 GPa and 2500 K, corresponding to conditions of the lowermost mantle. A perovskite to post-perovskite phase transition accounts for many unusual features of the D” region, including its notable seismic anisotropy, and also accounts for the unusual topology of the D” discontinuity. However, the experimentally synthesised post-perovskite phase of MgSiO3 is not quenchable to ambient conditions, which means that many of its physical properties remain difficult to determine. On the other hand, there are several post-perovskite oxides, CaIrO3, CaPtO3, CaRhO3 and CaRuO3, which can be quenched to ambient conditions, maintaining their structure. High pressure synthesis of CaIr1-xPtxO3 solid solutions (x = 0, 0.3, 0.5, 0.7) and CaIr0.5Rh0.5O3 was conducted at the University of Edinburgh and Geodynamics Research Center, Ehime University, and structures and physical properties of these novel post-perovskite materials determined. Substantial [100] grain growth was observed in all solid solutions leading to pronounced texture even in powdered materials. Temperature-independent paramagnetism above 150 K and small magnetic entropy observed in heat capacity measurements suggest that CaIrO3 is an intrinsically weak itinerant ferromagnetic metal, while electrical resistivity measurements show that it is a narrow bandgap semiconductor, possibly due to grain boundary effects. CaIrO3 undergoes a magnetic transition at 108K and possesses a saturated magnetic moment of 0.04 μB. Doping with Pt or Rh induces Curie-Weiss paramagnetism and suppresses the magnetic transition. The anisotropic structure and morphology of CaIrO3 combined with the Ir4+ spin-orbit coupling results in a large magnetic anisotropy constant of 1.77 x 106 Jm-3, comparable to values for permanent magnet materials. A new high-pressure phase of CaIr0.5Pt0.5O3 was synthesised at 60GPa, 1900K using a laser-heated DAC (diamond anvil cell) at GRC, Ehime University. Its Raman spectra resemble those of perovskite phases of CaIrO3 and CaMnO3, implying that CaIr0.5Pt0.5O3 undergoes a post-perovskite to perovskite phase transition with increasing pressure. I estimate an increase in thermodynamic Grüneisen parameter γth across the post-perovskite to perovskite transition of 34 %, with similar magnitude to (Mg,Fe)SiO3 and MgGeO3, suggesting that CaIr0.5Pt0.5O3 is a promising analogue for experimentally simulating the competitive stability between perovskite and post-perovskite phase of magnesium silicates in Earth’s lowermost mantle. Such estimation is reliable since the estimated and directly calculated thermodynamic Grüneisen parameter γth from heat capacity show consistent values. The marked effect that Pt has on stabilising the post-perovskite structure in CaIr1-xPtxO3 solid solutions explains why the post-perovskite to perovskite phase transition has not been observed for CaPtO3 in contrast to other quenchable post-perovskite oxides: CaIrO3, CaRhO3 and CaRuO3.Work presented here demonstrates that CaIrO3 solid solutions can be used to provide new insight into factors stabilising post-perovskite structures in Earth’s lowermost mantle.

Published
2011

23. Highly active and stable surface structure for oxygen evolution reaction originating from balanced dissolution and strong connectivity in BaIrO3 solid solutions

Author

Hirai, Shigeto, primary, Yagi, Shunsuke, additional, Oh, He-Chan, additional, Sato, Yoshiki, additional, Liu, Wei, additional, Liu, En-Pei, additional, Chen, Wei-Tin, additional, Miura, Akira, additional, Nagao, Masanori, additional, Ohno, Tomoya, additional, and Matsuda, Takeshi, additional

Published
2022
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28. Dehydroxylation and C[O.sub.2] incorporation in annealed mica (sericite): an infrared spectroscopic study

Author

Zhang, Ming, Wang, Ling, Hirai, Shigeto, Redfern, Simon A.T., and Salje, Ekhard K.H.

Subjects
Minerals -- Research, Mica -- Composition, Mica -- Thermal properties, Earth sciences
Abstract

Dehydroxylation and incorporation of C[O.sub.2] in mica (sericite-2[M.sub.1]) during high-temperature annealing has been investigated in detail using infrared (IR) spectroscopy. The dehydroxylation is characterized by a dramatic change of the OH ion spectrum and the appearance or development of different extra species (C[O.sub.2], C[O.sup.2-.sub.3], and O[H.sup.-]). A significant decrease in the K-O bond strength and a complex distortion of the silicon-oxygen tetrahedra were also observed. The general similarities between the spectra of the untreated and dehydroxylated sericite show that the layered framework is somewhat preserved in sericite dehydroxylate. The results suggest that the incorporation of C[O.sub.2] into the structures of the heated materials is associated with or enhanced by the dehydroxylation process, although the two processes have different reaction mechanisms. The C[O.sub.2] contents in heat-treated sericite show a correlation with the loss rate of hydroxyl. A weak O-H stretching absorption band near 3480 [cm.sup.-1] developed during dehydroxylation and it disappeared above 1100 [degrees]C. The results suggest that the developed additional O-H stretching signals and the thermally induced C[O.sub.2] do not structurally stabilize each other, as upon further heating the two different types of components vanished at different temperatures.

Published
2005

32. Wind tunnel test for Wind Turbines: Large Scale Horizontal Axis Wind Turbines

Author

Honda, Akihiro, Hirai, Shigeto, Karikomi, Kai, and Fukami, Koji

Abstract

第2回風洞技術の開発と応用シンポジウム: 風洞シンポジウム2013 (2013年10月11日. 清水建設株式会社技術研究所), 江東区, 東京, Symposium on Developments and Applications of Wind Tunnel Technologies 2nd meeting (October 11, 2013. Institute of Technology, SHIMIZU CORPORATION), Koto-ku, Toky, Japan, 形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: AA1530054007, レポート番号: JAXA-SP-15-021

Published
2016

34. Superconducting transition temperatures in the electronic and magnetic phase diagrams of Sr2VFeAsO3−δ , a superconductor

Author

Tojo, Yujiro, primary, Shibuya, Taizo, additional, Nakamura, Tetsuro, additional, Shoji, Koichiro, additional, Fujioka, Hirotaka, additional, Matoba, Masanori, additional, Yasui, Shintaro, additional, Itoh, Mitsuru, additional, Iimura, Soshi, additional, Hiramatsu, Hidenori, additional, Hosono, Hideo, additional, Hirai, Shigeto, additional, Mao, Wendy, additional, Kitao, Shinji, additional, Seto, Makoto, additional, and Kamihara, Yoichi, additional

Published
2019
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42. Ca1−xSrxRuO3 perovskite at the metal–insulator boundary as a highly active oxygen evolution catalyst.

Author

Hirai, Shigeto, Ohno, Tomoya, Uemura, Ren, Maruyama, Takahiro, Furunaka, Masaya, Fukunaga, Ryo, Chen, Wei-Tin, Suzuki, Hisao, Matsuda, Takeshi, and Yagi, Shunsuke

Abstract

The oxygen evolution reaction (OER) plays a key role in the electrode reactions of emerging energy conversion technologies such as water splitting and rechargeable metal–air batteries. Herein, we report that stronger electron–electron correlation leads to higher OER activity by a systematic electrochemical study of Ca1−xSrxRuO3. Specifically, we find that when the conducting material is sufficiently near the metal–insulator boundary (Ca0.9Sr0.1RuO3 in this study), it leads to a remarkable activity enhancement by a factor of 17. Our finding suggests that electron correlation not only enhances the initial OER activity but also stabilizes the structure of the catalyst. Therefore, the coexistence of metallic conductivity and strong electron correlation is beneficial for developing highly active OER catalysts. Furthermore, the excellent OER activity at x∼ 0.1 is accompanied by superior bifunctionality toward the OER and the oxygen reduction reaction (ORR). Our study also revealed that conducting materials close to the metal–insulator boundary are promising oxygen reaction catalysts for energy conversion technologies. [ABSTRACT FROM AUTHOR]

Published
2019
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50. ねじれフラッター振動の発生機構に関する研究

Author

MATSUMOTO, Masaru, SHIRAISHI, Naruhito, SHIRATO, Hiromichi, HIRAI, Shigeto, ITOH, Yuichi, and SHIGETAKA, Koichi

Subjects
Physics::Fluid Dynamics, 501.24
Abstract

This study aims the clarification of torsional flutter characteristics of H-section with variousslenderness ratio B/D. Its dynamic response is classified into three types in dependence onslenderness ratio, that is, restricted oscillation type, divergent oscillation type and stable type.Effect of turbulence is drastically affected by slenderness ratio. For example the restrictedoscillation tends to change to divergent one. In the case of divergent oscillation, flutter onsetvelocity increases with turbulence.

Published
1990

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