Updated on 2024/07/16

写真a

 
OOMURA Ayako
 
Organization
Academic Assembly Institute of Science and Technology Fundamental Sciences Associate Professor
Faculty of Science Associate Professor
Graduate School of Science and Technology Fundamental Sciences Associate Professor
Title
Associate Professor
External link

Degree

  • 博士(理学) ( 2004.3   お茶の水女子大学 )

Research Interests

  • 低温物性

  • 放射光X線回折

  • 高圧物性

Research Areas

  • Natural Science / Magnetism, superconductivity and strongly correlated systems

Research History (researchmap)

  • Niigata University   Associate Professor

    2018.10

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  • Niigata University   Institute for Research Promotion   Assistant Professor

    2017.4 - 2018.9

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  • Niigata University   Institute for Research Promotion, Center for Transdisciplinary Research   Assistant Professor

    2011.4 - 2017.3

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  • Niigata University   Center for Transdisciplinary Research   Assistant Professor

    2008.1 - 2011.3

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  • 東北大学大学院   工学研究科   研究支援者

    2006.9 - 2007.12

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  • Japan Atomic Energy Agency

    2005.10 - 2006.8

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  • 日本原子力研究所 関西研究所   放射光科学研究センター   博士研究員

    2004.4 - 2005.9

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Research History

  • Niigata University   Graduate School of Science and Technology Fundamental Sciences   Associate Professor

    2018.10

  • Niigata University   Institute for Research Promotion   Assistant Professor

    2017.4 - 2018.9

  • Niigata University   Institute for Research Promotion Center for Transdisciplinary Research   Assistant Professor

    2011.4 - 2017.3

  • Niigata University   Center for Transdisciplinary Research   Assistant Professor

    2008.1 - 2011.3

Education

  • Ochanomizu University   人間文化研究科   複合領域科学専攻

    2001.4 - 2004.3

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  • Ochanomizu University   人間文化研究科   物質科学専攻

    1999.4 - 2001.3

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  • Ochanomizu University   Faculty of Science   Division of Physics

    1995.4 - 1999.3

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Professional Memberships

  • THE PHYSICAL SOCIETY OF JAPAN

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  • THE JAPANESE SOCIETY FOR SYNCHROTRON RADIATION RESEARCH

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  • THE JAPAN SOCIETY OF HIGH PRESSURE SCIENCE AND TECHNOLOGY

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Committee Memberships

  •   高エネルギー加速器研究機構物質構造科学研究所 PF-User Association, 高圧ユーザーグループ代表  

    2024.4   

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  • 日本高圧力学会   評議員 会計幹事  

    2021.9 - 2023.8   

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    Committee type:Academic society

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  • 高エネルギー加速器研究機構 物質構造科学研究所 放射光実験施設   放射光共同利用実験審査委員会委員(PF-PAC)  

    2021.4   

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  • 日本高圧力学会   評議員  

    2017.9 - 2019.8   

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    Committee type:Academic society

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  • PFニュース編集委員会   編集委員  

    2014.4 - 2016.3   

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    Committee type:Academic society

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Papers

  • Pressure-induced large valence transitions in Yb-Cu binary intermetallic systems Reviewed

    Hitoshi Yamaoka, Ayako Ohmura, Naohito Tsujii, Hirofumi Ishii, Nozomu Hiraoka, Hitoshi Sato, Masahiro Sawada

    Physical Review B   109 ( 15 )   2024.4

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    Authorship:Corresponding author   Publishing type:Research paper (scientific journal)   Publisher:American Physical Society (APS)  

    DOI: 10.1103/physrevb.109.155147

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.109.155147/fulltext

  • Valence Transitions in Yb<sub>1+</sub><i><sub>x</sub></i>In<sub>1−</sub><i><sub>x</sub></i>Cu<sub>4</sub> Studied by High-resolution X-ray Absorption Spectroscopy, X-ray Diffraction, and Photoelectron Spectroscopy Reviewed

    Hitoshi Yamaoka, Shunsuke Yamanaka, Ayako Ohmura, Naohito Tsujii, Jaroslav Valenta, Yusaku Furue, Hitoshi Sato, Hirofumi Ishii, Nozomu Hiraoka, Chishiro Michioka, Hiroaki Ueda, Kazuyoshi Yoshimura

    Journal of the Physical Society of Japan   91 ( 12 )   2022.12

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    Publishing type:Research paper (scientific journal)   Publisher:Physical Society of Japan  

    DOI: 10.7566/jpsj.91.124701

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  • Phase Transition in Fluid Hydrogen at Room Temperature Reviewed

    Atsuko Nakayama, Yuya Isurugi, Yuya Serizawa, Satoshi Nakano, Ayako Ohmura, Fumihiro Ishikawa

    Journal of the Physical Society of Japan   91 ( 9 )   2022.9

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    <title>Abstract</title>
    The presence of phase-transition in hydrogen (H<sub>2</sub>) at around 560 megapascal (MPa) and room temperature was clarified by Raman and x-ray diffraction studies on both pure H<sub>2</sub> and graphite-H<sub>2</sub> mixture. H<sub>2</sub> is intercalated into the nano-space of graphite, which lowers the transition pressure and temporally expands the size of the honeycomb lattice of graphite under pressure up to 600 MPa. It is supposed that is caused by a gas-liquid phase-transition. According to the peak analysis for <italic>Q</italic><sub>1</sub>(<italic>J</italic>) mode, the ortho-para conversion of H<sub>2</sub> gradually begins to appear after the phase-transition pressure even at room temperature, while peak separation is difficult to achieve under pressure above 1.6 gigapascal (GPa) because of significant overlapping of the peak intensities. Because we have missed the ortho-para conversion which could be observed in only such a small pressure range, the fluid phase at room temperature was full of mystery.

    DOI: 10.7566/jpsj.91.093601

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  • Direct Observation of Pressure-induced Yb Valence Transition in YbInCu4 Reviewed

    Hitoshi Yamaoka, Ayako Ohmura, Yusaku Furue, Naohito Tsujii, Hirofumi Ishii, Nozomu Hiraoka

    Journal of the Physical Society of Japan   90 ( 12 )   124801   2021.12

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    The Yb valence state of YbInCu4 was measured at 300 and 13 K under pressure by high-resolution x-ray absorption spectroscopy (XAS). The electronic structure of Cu was also measured by XAS at the Cu-K absorption edge. Pressureinduced disappearance of the valence transition was observed directly at 13 K. The present results suggest a charge transfer from Yb to Cu sites at 13 K after the disappearance of the valence transition under pressure.

    DOI: 10.7566/jpsj.90.124801

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  • Superconducting and structural properties of the type-I superconductor PdTe2 under high pressure Reviewed

    Yusaku Furue, Tadachika Fujino, Marc V. Salis, Huaqian Leng, Fumihiro Ishikawa, Takashi Naka, Satoshi Nakano, Yingkai Huang, Anne de Visser, Ayako Ohmura

    Physical Review B   104 ( 14 )   144510   2021.10

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    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Physical Society (APS)  

    The transition metal dichalcogenide PdTe2 has attractive features based on its classification as a type-II Dirac semimetal and the occurrence of type-I superconductivity, providing a platform for discussion of a topological superconductor. Our recent work revealed that type-I superconductivity persists up to pressures of similar to 2.5 GPa and the superconducting transition temperature T-c reaches a maximum at around 1 GPa, which is inconsistent with the theoretical prediction. To understand its nonmonotonic variation and investigate superconductivity at higher pressures, we performed structural analysis by x-ray diffraction at room temperature below 8 GPa and electrical resistivity measurements at low temperatures from 1 to 8 GPa. With regard to the superconductivity beyond 1 GPa, the monotonic decrease in T-c is reproduced without any noticeable anomalies; T-c changes from 1.8 K at 1 GPa to 0.82 K at 5.5 GPa with dT(c)/dP similar to -0.22 K/GPa. The crystal structure with space group P (3) over bar m1 is stable in the pressure range we examined. On the other hand, the normalized pressure-strain analysis (finite strain analysis) indicates that the compressibility changes around 1 GPa, suggesting that a Lifshitz transition occurs. We here discuss the effect of pressure on the superconducting and structural properties based on the comparison of these experimental results.

    DOI: 10.1103/physrevb.104.144510

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.104.144510/fulltext

  • The microscopic transition process from high-density to low-density amorphous state of SnI4 Reviewed

    Kazuhiro Fuchizaki, Ayako Ohmura, Hiroki Naruta, Takuya Nishioka

    Journal of Physics: Condensed Matter   33   365401   2021.7

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    Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

    DOI: 10.1088/1361-648x/ac0dd7

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    Other Link: https://iopscience.iop.org/article/10.1088/1361-648X/ac0dd7/pdf

  • Cluster glass transition and relaxation in the random spinel CoGa2O4 Reviewed

    T. Naka, T. Nakane, S. Ishii, M. Nakayama, A. Ohmura, F. Ishikawa, A. de Visser, H. Abe, T. Uchikoshi

    Physical Review B   103 ( 22 )   224408   2021.6

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    DOI: 10.1103/physrevb.103.224408

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    Other Link: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.103.224408/fulltext

  • Do SnI4 molecules deform on heating and pressurization in the low-pressure crystalline phase? Reviewed

    Hiroki Naruta, Kazuhiro Fuchizaki, Daisuke Wakabayashi, Akio Suzuki, Ayako Ohmura, Hiroyuki Saitoh

    Journal of Physics: Condensed Matter   32 ( 5 )   055401 - 055401   2020.1

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    A SnI4 molecule lowers its symmetry from T-d to C-3v on the liquid-liquid transition. Because it is possible to lower the molecular symmetry without violating the crystalline symmetry, it is worth examining whether the deformation occurs in the crystalline phase field. Extended x-ray absorption fine structure (EXAFS) measurements on the crystalline state were carried out to investigate the change in the environment around a Sn atom at high pressures and temperatures. We could not find clear evidence on the symmetry change of molecules even close to the melting points, where the melting curve becomes abnormally flat against pressure. Indeed, no inconsistency was found when we assumed that the coordination number of a Sn atom remains unchanged in the temperature and pressure range examined. The situation remains true when the system entered the high-pressure crystalline phase on compression. We can propose a consistent scenario as to the structural change on the phase transformation. The incompressibility of a SnI4 molecule could be suitably quantified. The procedure enabled us to conclude the molecule is more than an order of magnitude incompressible than the lattice.

    DOI: 10.1088/1361-648x/ab4cbc

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    Other Link: http://iopscience.iop.org/article/10.1088/1361-648X/ab4cbc/pdf

  • Superconductivity under pressure in the Dirac semimetal PdTe2 Reviewed

    H Leng, A Ohmura, L N Anh, F Ishikawa, T Naka, Y K Huang, A de Visser

    Journal of Physics: Condensed Matter   32 ( 2 )   025603 - 025603   2020.1

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    DOI: 10.1088/1361-648x/ab49b5

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    Other Link: http://iopscience.iop.org/article/10.1088/1361-648X/ab49b5/pdf

  • Transport and structural properties of Cu0.25Bi2(TexSe1-x)3 (x = 0.01) under high pressure Reviewed

    Ayako Ohmura, Masako Matsuzawa, Fumihiro Ishikawa, Yusuke Suzuki, Masashi Komatsu, Shumpei Osuga, Satoshi Nakano, Atsuko Nakayama, Yuh Yamada, Takanari Kashiwagi, Kazuo Kadowaki

    Japanese Journal of Applied Physics   56 ( 5 )   2017.5

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    Cu0.25Bi2(TexSe1-x)3 is a material in which tellurium atoms (Te) partially occupy selenium (Se) sites in a crystal structure of the superconductor Cu0.25Bi2Se3. This study focuses on the composition of x = 0.01, Cu0.25Bi2(Te0.01Se0.99)3, and we performed electrical resistivity measurement and X-ray diffraction under high pressures. Cu0.25Bi2(Te0.01Se0.99)3 shows slight diamagnetism and a drop in resistivity at ambient pressure
    this suggests possible superconductivity at the transition temperature of Tc = 3.2 K, which is suppressed at P = 1 GPa. On further compression, a slight drop in resistivity is observed at temperatures of 4.3-5.4 K above 10 GPa. This drop is suppressed under magnetic fields, suggesting the occurrence of superconducting transition. The pressure-induced structural phase transition from a trigonal R3m phase to a sevenfold monoclinic C2/m phase occurs at 10.9 GPa. These results suggest that the superconducting transition above 10 GPa occurs in the high-pressure C2/m phase.

    DOI: 10.7567/JJAP.56.05FB04

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  • Pressure-induced topological phase transition in the polar semiconductor BiTeBr Reviewed

    Ayako Ohmura, Yuichiro Higuchi, Takayuki Ochiai, Manabu Kanou, Fumihiro Ishikawa, Satoshi Nakano, Atsuko Nakayama, Yuh Yamada, Takao Sasagawa

    PHYSICAL REVIEW B   95 ( 12 )   2017.3

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    We performed x-ray diffraction and electrical resistivity measurement up to pressures of 5 GPa and the first-principles calculations utilizing experimental structural parameters to investigate the pressure-induced topological phase transition in BiTeBr having a noncentrosymmetric layered structure (space group P3m1). The P3m1 structure remains stable up to pressures of 5 GPa; the ratio of lattice constants c/a has a minimum at pressures of 2.5-3 GPa. In the same range, the temperature dependence of resistivity changes frommetallic to semiconducting at 3 GPa and has a plateau region between 50 and 150 K in the semiconducting state. Meanwhile, the pressure variation of band structure shows that the bulk band-gap energy closes at 2.9 GPa and re-opens at higher pressures. Furthermore, according to the Wilson loop analysis, the topological nature of electronic states in noncentrosymmetric BiTeBr at 0 and 5 GPa are explicitly revealed to be trivial and nontrivial, respectively. These results strongly suggest that pressure-induced topological phase transition in BiTeBr occurs at the pressures of 2.9 GPa.

    DOI: 10.1103/PhysRevB.95.125203

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  • 21aPS-30 Pressure dependence of transport properties of K(Fe_<1-x>Co_x)_2As_2

    Yamagishi T., Ishikawa F., Okaji R., Ishii A., Nakayama A., Ohmura A., Yamada Yuh

    Meeting Abstracts of the Physical Society of Japan   71   2227 - 2227   2016

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    Language:Japanese   Publisher:The Physical Society of Japan (JPS)  

    DOI: 10.11316/jpsgaiyo.71.1.0_2227

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  • 21aPS-38 Single-crystal growth of Pr_2Ba_4Cu_7O_<15-δ> under oxygen pressure

    Inaba K., Ishikawa F., Hoshito S., Sato C., Iwata N., Sumi Y., Nakayama A., Ohmura A., Yamada Yuh

    Meeting Abstracts of the Physical Society of Japan   71   2233 - 2233   2016

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    DOI: 10.11316/jpsgaiyo.71.1.0_2233

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  • 19pBG-8 Search for post-graphite phase under high pressure at room temperature

    Sato Takaaki, Nakayama Atsuko, Taniguchi Takashi, Yamada Yuh, Ishikawa Fumihiro, Ohmura Ayako

    Meeting Abstracts of the Physical Society of Japan   71   1850 - 1850   2016

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    DOI: 10.11316/jpsgaiyo.71.1.0_1850

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  • Counting graphene layers based on the light-shielding effect of Raman scattering from a substrate Reviewed

    Atsuko Nakayama, Suguru Hoshino, Yuh Yamada, Ayako Ohmura, Fumihiro Ishikawa

    APPLIED PHYSICS LETTERS   107 ( 23 )   2015.12

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    We present a method for determining the number of stacked layers in graphene by exploiting its light-shielding effect. If a substrate supporting graphene has Raman-active modes, its Raman bands can be obtained simultaneously with the G and G' bands of graphene. The Raman intensities from the substrate decrease with increasing the number of graphene layers because of the low opacity of graphene for visible light. The relationship between the number of graphene layers n and the relative intensities I-n,I-h/I-0,I-h from the substrate can be represented by I-n,I-h/I-0,I-h = 0.977(2n), on the basis of the optical transmittance of visible light for single-layer graphene. The method is simple, convenient, highly accurate, and can be used to count beyond six layers up to 30 layers. (C) 2015 AIP Publishing LLC.

    DOI: 10.1063/1.4937140

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  • Collapse of CuO Double Chains and Suppression of Superconductivity in High-Pressure Phase of YBa2Cu4O8 Reviewed

    Atsuko Nakayama, Yusuke Onda, Shuhei Yamada, Hiroshi Fujihisa, Masafumi Sakata, Yuki Nakamoto, Katsuya Shimizu, Satoshi Nakano, Ayako Ohmura, Fumihiro Ishikawa, Yuh Yamada

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   83 ( 9 )   2014.9

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    The crystal structure and electrical resistivity of YBa2Cu4O8 (Y124) were studied under high pressure up to 18 GPa using diamond-anvil cells, respectively, in order to clarify its conduction mechanism. Y124 causes the first-order phase-transition into the orthorhombic Immm at pressure around 11 GPa. The high-pressure phase (HPP) also shows the superconductivity, while the manner of temperature dependence of electrical resistance and the pressure dependence of transition temperature, T-c, drastically change above 11 GPa. The CuO2 plane persists in HPP but the CuO double chains collapse with the phase transition and transform into three-dimensional Cu-O network, resulting in the renewal of conduction system.

    DOI: 10.7566/JPSJ.83.093601

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  • Pressure-induced superconductivity in non-stoichiometric bismuth telluride Bi35Te65 Reviewed

    M. Einaga, A. Ohmura, F. Ishikawa, A. Nakayama, Yuh Yamada, S. Nakano, A. Matsushita, K. Shimizu

    Journal of Physics: Conference Series   500 ( 19 )   192003 - 192003   2014.5

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    We performed x-ray diffraction study and electrical resistivity measurement of non-stoichiometric n-type Bi35Te65 under high pressure to investigate pressure-induced superconductivity and structural phase transition. Stoichiometric bismuth telluride (Bi2Te3), which is a p-type semiconductor, has the rhombohedral structure with space group R-3m at ambient condition. Pressure-induced superconductivity of stoichiometric p-type Bi2Te3 occurs in the high-pressure phases which appear above 8 GPa. Bi35Te65 has also the R-3m structure at ambient condition with electron carriers. X-ray diffraction study shows that the R-3m structure remains stable up to 8 GPa at room temperature. The superconducting transition in n-type Bi35Te65 is observed above 6 GPa; the transition temperature is 2.9 K at 6 GPa. The electrical resistivity at room temperature decreases rapidly at pressures from 7 to 8 GPa, indicating the occurrence of structural phase transition. It suggests that the superconducting transition at 6 GPa occurs at the ambient pressure phase with the R-3m structure. © Published under licence by IOP Publishing Ltd.

    DOI: 10.1088/1742-6596/500/19/192003

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    Other Link: http://stacks.iop.org/1742-6596/500/i=19/a=192003?key=crossref.8d7c46d38fa902a5f912a42321d7a12e

  • Synthesis of New Layered Oxypnictides Sr2CrO2(FeAs)(2) Reviewed

    Naoya Eguchi, Fumihiro Ishikawa, Michihiro Kodama, Takeshi Wakabayashi, Atsuko Nakayama, Ayako Ohmura, Yuh Yamada

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   82 ( 4 )   2013.4

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    DOI: 10.7566/JPSJ.82.045002

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  • Report on the 24<sup>th</sup> Biennial International Conference of the International Association for the Advancement of High Pressure Science and Technology (AIRAPT) (I)

    OHMURA Ayako

    The Review of High Pressure Science and Technology   23 ( 4 )   354 - 355   2013

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    Language:Japanese   Publisher:The Japan Society of High Pressure Science and Technology  

    DOI: 10.4131/jshpreview.23.354

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  • Powder x-ray diffraction of BaFe2As2under hydrostatic pressure Reviewed

    N Eguchi, M Kodama, F Ishikawa, A Nakayama, A Ohmura, Yuh Yamada, S Nakano

    Journal of Physics: Conference Series   400 ( 2 )   022017 - 022017   2012.12

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    We have performed powder x-ray diffraction study on BaFe2As 2 under hydrostatic pressures up to 6 GPa at room temperature. Hydrostatic pressure was produced by means of a diamond anvil cell with He gas as a pressure transmitting medium. Single crystalline sample of BaFe 2As2 was ground in alumina mortar cooled with liquid nitrogen to produce a fine powder sample. The diffraction patterns show a tetragonal structure with a space group of I4/mmm in the whole pressure range. Rietveld analysis on the experimental results shows that the lattice parameters are monotonically decreased with increasing pressure. The As-Fe-As bond angle does not reach the ideal tetrahedral value of 109.47°. © Published under licence by IOP Publishing Ltd.

    DOI: 10.1088/1742-6596/400/2/022017

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  • Pressure-induced superconductivity in Bi0.85Sb0.15 alloy Reviewed

    A. Ohmura, A. Yamamura, M. Einaga, F. Ishikawa, A. Nakayama, Yuh Yamada, S. Nakano

    Journal of Physics: Conference Series   400 ( PART 2 )   2012.1

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    Pressure variation of the electrical and structural properties of bismuth-antimony alloy at the composition of x = 0.15 (Bi0.85Sb 0.15) has been studied by electrical resistivity and synchrotron radiation x-ray diffraction measurements up to 10 GPa. The crystal structure changes from the A7 structure to the incommensurate host-guest composite one at 3 GPa and room temperature. Temperature dependence of the resistivity greatly changes from the semiconducting behaviour to the metallic one associated with the structural phase transition. Pressure-induced superconducting transition of Bi0.85Sb0.15 is observed above 4.5 GPa. The transition temperature Tc is found to decrease from 6.79 GPa at 4.5 GPa to 5.82 K at 9.5 GPa with increasing pressure. © Published under licence by IOP Publishing Ltd.

    DOI: 10.1088/1742-6596/400/2/022088

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  • Pressure effect on critical temperature for superconductivity and lattice parameters of AlB2-type ternary silicide YbGa1.1Si0.9 Reviewed

    Ayako Ohmura, Koji Fujimaki, Fumihiro Ishikawa, Yuh Yamada, Naohito Tsujii, Motoharu Imai

    PHYSICAL REVIEW B   84 ( 10 )   2011.9

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    Electrical resistivity and x-ray diffraction measurements have been carried out to investigate the pressure effect on the critical temperature for superconductivity (T-C) and lattice parameters ofAlB(2)-type superconducting silicide YbGa1.1Si0.9 (T-C = 2.4 K) and its referencematerial CaGaSi (T-C = 4.5 K). The electrical resistivity measurements up to 2.5 GPa reveal that T-C decreases with pressure for both silicides and the pressure derivative of T-C (dT(C)/dP) is -0.78 K/GPa and -0.026 K/GPa for YbGa1.1Si0.9 and CaGaSi, respectively. X-ray diffraction measurements up to 3.5 GPa indicate both silicides do not exhibit structural changes in this pressure range and they have similar values for the bulk moduli: B-0 = 40 +/- 2 GPa for YbGa1.1Si0.9 and B-0 = 42 +/- 1 GPa for CaGaSi. The relative pressure derivative of T-C (dlnT(C)/dP) and logarithmic volume derivative of T-C (dlnT(C)/dlnV) are -0.33 GPa(-1) and 13 in YbGa1.1Si0.9. These values are about tenfold larger than those for other AlB2-type superconductors. Additionally, the origin of dlnT(C)/dP and dlnT(C)/dlnV in YbGa1.1Si0.9 relative to the pressure effect on the valence of Yb atoms is discussed.

    DOI: 10.1103/PhysRevB.84.104520

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  • High-pressure study of ScH3: Raman, infrared, and visible absorption spectroscopy Reviewed

    Tetsuji Kume, Hiroyuki Ohura, Tomoo Takeichi, Ayako Ohmura, Akihiko Machida, Tetsu Watanuki, Katsutoshi Aoki, Shigeo Sasaki, Hiroyasu Shimizu, Kenichi Takemura

    PHYSICAL REVIEW B   84 ( 6 )   2011.8

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    Raman, IR, and visible absorption spectra of scandium trihydride (ScH3) have been measured at high pressures up to 50 GPa, to investigate the structural and electronic phase transitions. Successive hcp-intermediate-fcc phase transitions were observed at 25 and 46 GPa by Raman and IR measurements. It was suggested that the intermediate phase of ScH3 takes the same structure as that of YH3 with a long periodicity of the stacking of the metal planes. The visible absorption spectra allowed us to determine that the energy gap of ScH3 is 1.7 eV at the ambient condition and is closed around 50 GPa, at which the crystal structure transforms to fcc.

    DOI: 10.1103/PhysRevB.84.064132

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  • Pressure-induced phase transition of Bi2Te3 to a bcc structure Reviewed

    Einaga Mari, Ohmura Ayako, Nakayama Atsuko, Ishikawa Fumihiro, Yamada Yuh, Nakano Satoshi

    PHYSICAL REVIEW B   83 ( 9 )   2011.3

  • Site dependent hardening of the lanthanum metal lattice by hydrogen absorption Reviewed

    A. Machida, T. Watanuki, A. Ohmura, T. Ikeda, K. Aoki, S. Nakano, K. Takemura

    SOLID STATE COMMUNICATIONS   151 ( 5 )   341 - 345   2011.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:PERGAMON-ELSEVIER SCIENCE LTD  

    The compressibility of lanthanum (La) metal and its hydrides were measured at room temperature by high pressure synchrotron X-ray diffraction. La metal pressurized in a hydrogen medium forms a hydride with an fcc metal lattice, which likely contains hydrogen at a concentration close to 3.0 and persists over the measured pressure span up to 21 GPa. Equations of state have been determined by helium compression experiments for LaH2 with tetrahedral interstitial sites fully occupied with hydrogen atoms and for LaH2.46 with octahedral interstitial sites partially occupied with hydrogen atoms and tetrahedral sites fully occupied. Both hydrides possess fcc metal lattices. The bulk modulus values B-0 are 66.7 +/- 1.2 GPa for LaH2 and 68.4 +/- 1.0 GPa for LaH2.46. These values are three times larger than that of La metal and are very close to each other despite the difference in hydrogen occupation states. The hardening of the metal lattice by hydrogenation is attributed predominantly to hydrogen-metal interactions at the tetrahedral sites and is most pronounced for La, which has the largest ionic radius among rare-earth metals. (C) 2010 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ssc.2010.12.030

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  • Pressure-induced phase transition, metallization, and superconductivity in boron triiodide Reviewed

    Nozomu Hamaya, Miyuki Ishizuka, Suzue Onoda, Jiang Guishan, Ayako Ohmura, Katsuya Shimizu

    Physical Review B - Condensed Matter and Materials Physics   82 ( 9 )   2010.9

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    Pressure evolution of structural and electrical properties of boron triiodide, a highly anisotropic molecular crystal consisting of stacked layers of planar BI3 molecules, has been studied by x-ray diffraction and resistivity measurements. A new phase transition was observed to occur at 6.2 GPa from the molecular phase with hexagonal structure to a monatomic phase with the face-centered-cubic lattice of iodine atoms. This first-order phase transition is characterized by the discontinuous crush of stacking of molecular layers. The monatomic phase becomes metallic at ∼23?GPa and exhibits superconductivity above ∼27?GPa. The process of molecular dissociation and electrical properties of BI3 are discussed in comparison with those of iodine and other simple molecular iodides. © 2010 The American Physical Society.

    DOI: 10.1103/PhysRevB.82.094506

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  • Powder x-ray diffraction study of Ne up to 240 GPa Reviewed

    K. Takemura, T. Watanuki, K. Ohwada, A. MacHida, A. Ohmura, A. Ohmura, K. Aoki

    Journal of Physics: Conference Series   215   2010.5

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    Powder x-ray diffraction experiments have been done on Ne up to 237 GPa at room temperature. Ne remains in the fcc phase up to the highest pressure. In order to observe the weak 200 reflection at ultrahigh pressures, we have used the tube-cross slit at the exit side of x-rays, which effectively reduced the scattered x-rays by the diamond anvil. The lattice parameters obtained from the 111 and 200 reflections significantly differ from each other, implying the existence of sizable uniaxial stress in Ne at ultrahigh pressures. On the basis of the calculated elastic constants of Ne at high pressures, we conclude that the 111 reflection is least affected by the uniaxial stress. The equation of state constructed from the 111 reflection agrees well with previous data. © 2010 IOP Publishing Ltd.

    DOI: 10.1088/1742-6596/215/1/012017

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  • New superconducting phase of Bi2Te3under pressure above 11 GPa Reviewed

    M. Einaga, Y. Tanabe, A. Nakayama, A. Ohmura, F. Ishikawa, Yuh Yamada

    Journal of Physics: Conference Series   215   012036 - 012036   2010.3

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    We have investigated the pressure dependence of superconducting transition temperature Tc of Bi2Te3 through electrical resistance measurement under high pressure up to 13 GPa. The value of zero-resistance critical-temperature Tczero is 2.7 K at 9.0 GPa. Pressurization up to 11 GPa reduces the Tczero. However the pressurization at 13 GPa causes sudden enhancement of T czero, which is obtained to be 3.7 K. The onset temperature of superconducting transition Tconset shows the positive pressure dependence under pressure above 10 GPa. The value of Tconset is obtained to be 5.0 K at 13 GPa. The sharp increase of Tczero and the positive pressure dependence of Tconset suggest a presence of new superconducting phase. © 2010 IOP Publishing Ltd.

    DOI: 10.1088/1742-6596/215/1/012036

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  • High pressure raman and visible absorption study of AlH<SUB>3</SUB> Reviewed

    N. Shimura, T. Takeichi, T. Kume, S. Sasaki, H. Shimizu, A. Ohmura, K. Ikeda, Y. Nakamori, S. Orimo

    Journal of Physics: Conference Series   215 ( 1 )   012047-1 - 012047-4   2010.3

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    DOI: 10.1088/1742-6596/215/1/012047

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  • Photocatalytic activities of Ba2RBiO6 (R = La, Ce, Nd, Sm, Eu, Gd, Dy) under visible light irradiation Reviewed

    Takuya Hatakeyama, Shingo Takeda, Fumihiro Ishikawa, Ayako Ohmura, Atsuko Nakayama, Yuh Yamada, Akiyuki Matsushita, Jinhua Yea

    JOURNAL OF THE CERAMIC SOCIETY OF JAPAN   118 ( 1374 )   91 - 95   2010.2

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    We succeeded in synthesizing Ba2RBiO6 (R = La, Ce, Nd, Sm, Eu, Gd, and Dy) with a double-perovskite structure. Its photocatalytic activities were then investigated for a degradation of methylene blue (MB) solution and gaseous 2-propanol (IPA). High photocatalytic activities were observed under visible light irradiation and also a rare earth dependence of photocatalytic activities in the IPA degradation. We carried out first-principle calculations of the band structure based on the all-electron Full-potential Linear Augmented Plane-Wave (FLAPW) method and discuss the relationship between the high photocatalytic activities and the band structure in this paper. (C) 2010 The Ceramic Society of Japan. All rights reserved.

    DOI: 10.2109/jcersj2.118.91

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  • Pressure dependence of superconducting-transition temperature of YbGa1.1Si0.9

    A. Ohmura, K. Fujimaki, M. Einaga, F. Ishikawa, A. Nakayama, Yuh Yamada, M. Imai, N. Tsujii

    Journal of Physics: Conference Series   215   012035   2010

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    Pressure dependence of the superconducting transition temperature T-c has been investigated in YbGa1.1Si0.9, which is the AlB2-type layered superconductor with T-c = 2.4 K. The electrical resistivity measurements were carried out under hydrostatic pressure up to 2.5 GPa using a piston-cylinder type pressure cell. With increasing pressure, the T-c of YbGa1.1Si0.9 decreases from 2.4 K to 1.1 K at 2.5 GPa with a pressure derivative of T-c, dT(c)/dP, of -0.78 K/GPa. This negative pressure derivative of T-c is similar to the other superconducting AlB2-type silicides. The relative pressure derivative of T-c, dlnT(c)/dP, for YbGa1.1Si0.9 is - 0.33 GPa(-1), which is about ten times larger than those for other layered superconductors.

    DOI: 10.1088/1742-6596/215/1/012035

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  • Structure of pressure-induced amorphous form of SnI4 at high pressure Reviewed

    Ayako Ohmura, Kyoko Sato, Nozomu Hamaya, Maiko Isshiki, Yasuo Ohishi

    Physical Review B - Condensed Matter and Materials Physics   80 ( 5 )   2009.8

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    The structure of pressure-induced amorphous form of SnI4 has been studied by synchrotron x-ray diffraction measurements using diamond-anvil cell. The structure factor, the reduced radial distribution function, and the density were obtained between 25 and 55 GPa. Comparison of measured structure factor with that calculated for a randomly oriented dimerized molecules model shows no similarity between them. Experimentally obtained radial distribution function provides clear evidence for the absence of both distances between tin and iodine atoms and between iodine atoms within the SnI4 tetrahedral molecule. Characteristic features of the structure factor for amorphous SnI4 show a marked resemblance to those for elemental metallic glasses which are successfully reproduced by a model of dense random packing of equal-sized spheres. Indeed, various quantities such as positions of peaks in measured structure factors and in experimental radial distribution functions, the coordination number are in precise agreement with those derived from the dense random-packing model. We conclude that the structure of the high-pressure amorphous form of SnI4 is the relatively rigid packing of tetrahedra composed of iodine and substitutional tin atoms. © 2009 The American Physical Society.

    DOI: 10.1103/PhysRevB.80.054201

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  • Structure of pressure-induced amorphous form of SnI4 at high pressure Reviewed

    Ayako Ohmura, Kyoko Sato, Nozomu Hamaya, Maiko Isshiki, Yasuo Ohishi

    PHYSICAL REVIEW B   80 ( 5 )   2009.8

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    The structure of pressure-induced amorphous form of SnI4 has been studied by synchrotron x-ray diffraction measurements using diamond-anvil cell. The structure factor, the reduced radial distribution function, and the density were obtained between 25 and 55 GPa. Comparison of measured structure factor with that calculated for a randomly oriented dimerized molecules model shows no similarity between them. Experimentally obtained radial distribution function provides clear evidence for the absence of both distances between tin and iodine atoms and between iodine atoms within the SnI4 tetrahedral molecule. Characteristic features of the structure factor for amorphous SnI4 show a marked resemblance to those for elemental metallic glasses which are successfully reproduced by a model of dense random packing of equal-sized spheres. Indeed, various quantities such as positions of peaks in measured structure factors and in experimental radial distribution functions, the coordination number are in precise agreement with those derived from the dense random-packing model. We conclude that the structure of the high-pressure amorphous form of SnI4 is the relatively rigid packing of tetrahedra composed of iodine and substitutional tin atoms.

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  • Zero-resistance superconducting phase in BaFe2As2 under high pressure Reviewed

    Fumihiro Ishikawa, Naoya Eguchi, Michihiro Kodama, Koji Fujimaki, Mari Einaga, Ayako Ohmura, Atsuko Nakayama, Akihiro Mitsuda, Yuh Yamada

    PHYSICAL REVIEW B   79 ( 17 )   2009.5

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    A single-crystalline sample of BaFe2As2 was prepared by high-pressure synthesis, and temperature dependence of resistivity was measured under high pressures of up to 9.0 GPa. Application of 3.0 GPa pressure suppresses the spin-density wave transition and induces superconductivity with the zero resistance state at a superconducting transition temperature T-c=35 K. T-c decreases monotonically with increasing pressure. The appearance of the superconductivity and the disappearance of the anomaly due to the spin-density wave transition occur simultaneously at a pressure of 3.0 GPa. At 3.0 GPa, a superconducting transition is induced in BaFe2As2; however, the superconductivity is suppressed at higher pressure.

    DOI: 10.1103/PhysRevB.79.172506

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  • Raman and optical absorption studies of rare-earth hydrides under high pressure Reviewed

    T. Kume, H. Ohura, T. Takeichi, S. Sasaki, H. Shimizu, A. Ohmura, A. Machida, T. Watanuki, K. Aoki, K. Takemura

    Journal of Physics: Conference Series   121   2008.12

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    Raman and visible absorption study were performed for YH3 and ScH3 at high pressures, in order to clarify the structural and electronic phase transitions. The Raman results of YH3 revealed the presence of an intermediate phase at 9-24 GPa between the low-pressure hexagonal and high-pressure fcc phases. The characteristic behaviour was commonly observed for vibrational properties of YH3 and ScH3, suggesting a common mechanism of the structural transformation. The results of the absorption measurements for YH3 demonstrate that the optical band gap starts to close in response to the phase transition. © 2008 IOP Publishing Ltd.

    DOI: 10.1088/1742-6596/121/4/042011

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  • Photochromism in yttrium hydride Reviewed

    Ayako Ohmura, Akihiko Machida, Tetsu Watanuki, Katsutoshi Aoki, Satoshi Nakano, K. Takemura

    APPLIED PHYSICS LETTERS   91 ( 15 )   2007.10

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    Transparent orange yttrium hydride turns to black when illuminated by visible laser light at pressures of several gigapascals at room temperature. The marked reduction in optical transmittance extends over the infrared region, suggesting that illumination creates persistent free carriers. The opaque black sample returns to the transparent orange hydride during room-temperature annealing for a few hours. Photochromism is pronounced for the coexistent state of the metallic fcc-YH2 and the insulating hexagonal-YH3 state but is depressed for the single phase of hexagonal-YH3. The results indicate that light illumination can modify the optical and possibly electronic properties during a certain period of times.

    DOI: 10.1063/1.2794755

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  • Pressure-induced Structural change from hexagonal to fcc metal lattice in scandium trihydride Reviewed

    A. Ohmura, A. Machida, T. Watanuki, K. Aoki, S. Nakano, K. Takemura

    J. Alloys Compd.   446-447   598 - 602   2007.10

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  • Long-period stacking structures in yttrium trihydride at high pressure Reviewed

    A. Machida, A. Ohmura, T. Watanuki, K. Aoki, K. Takemura

    Phys. Rev. B:   76 ( 5 )   052101-1 - 052101-4   2007.8

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  • High-pressure study of YH3 by Raman and visible absorption spectroscopy Reviewed

    Tetsuji Kume, Hiroyuki Ohura, Shigeo Sasaki, Hiroyasu Shimizu, Ayako Ohmura, Akihiko Machida, Tetsu Watanuki, Katsutoshi Aoki, Kenichi Takemura

    PHYSICAL REVIEW B   76 ( 2 )   2007.7

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    Raman and visible absorption spectra of YH3 were measured at high pressures, in order to clarify the structural and electronic phase transitions. The Raman results revealed the presence of an intermediate phase at 9-24 GPa between the low-pressure hexagonal and high-pressure fcc phases. The Y-framework structure and the position of interstitial H atoms are changed on the transition to intermediate phase. The results of the absorption measurements demonstrate that the optical band gap starts to close in response to the phase transition.

    DOI: 10.1103/PhysRevB.76.024107

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  • Development of a single-crystal X-ray diffraction system for hydrostatic-pressure and low-temperature structural measurement and its application to the phase study of quasicrystals Reviewed

    T. Watanuki, A. MacHida, T. Ikeda, A. Ohmura, H. Kaneko, K. Aoki, T. J. Sato, A. P. Tsai

    Philosophical Magazine   87 ( 18-21 )   2905 - 2911   2007.7

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    We constructed a single-crystal synchrotron X-ray diffraction system to precisely study the structure under hydrostatic pressure conditions at low temperatures and applied it to a study on the phase transition phenomena of a Cd-Yb periodic approximant and a Cd-Yb quasicrystal. Four phases were newly observed for the 1/1 approximant crystal in a P-T range up to 5.2 GPa and down to 10 K. The innermost part of the atomic clusters of Cd4 tetrahedra exhibited various orientational ordering sensitively depending on pressure and temperature. High pressure diffraction measurements using a highly parallel synchrotron X-ray beam and a hydrostatically compressed single crystal enabled us to detect the weak diffractions due to the subtle structural changes.

    DOI: 10.1080/14786430701358707

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  • X-ray diffraction investigation of the hexagonal-fcc structural transition in yttrium trihydride under hydrostatic pressure Reviewed

    A. Machida, A. Ohmura, T. Watanuki, T. Ikeda, K. Aoki, S. Nakano, K. Takemura

    Solid State Communications   138 ( 9 )   436 - 440   2006.6

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    Pressure induced structural transition of yttrium hydride has been investigated using synchrotron radiation X-ray diffraction measurement up to 24 GPa at room temperature. A reversible hexagonal-fcc transition with a wide intermediate region from 11 to 20 GPa is confirmed, which is consistent with previously reported X-ray results. The diffraction patterns measured for the intermediate state are not interpreted in terms of a hexagonal-fcc coexisting state or as rare-earth structures with various metal-layer stacking sequences. The equation of state determined for the hexagonal-YH3 provides a bulk modulus B0 of 71.9 GPa, which is nearly half of the previously reported value, but is within the range of values reported for other rare-earth metal trihydrides with hexagonal structures. © 2006 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ssc.2006.04.011

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  • Single Crystal Synchrotron X-Ray Diffraction Study under Pressure in UGe2 Reviewed

    Naofumi Aso, Kenji Ohwada, Tetsu Watanuki, Akihiko Machida, Ayako Ohmura, Toshiya Inami, Yoshiya Homma, Yoshinobu Shiokawa, Kazuma Hirota, Noriaki K. Sato

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   75   88 - 90   2006.1

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    Synchrotron radiation x-ray diffraction experiments on the pressure-induced ferromagnetic superconductor UGe2 has been performed using a diamond anvil cell (DAC)diffractometer to study the correlation between the crystal structure and ferromagnetism. The oscillation photos covering the three-dimensional reciprocal spaces were taken both below and above a critical I entperai uni T-x at pressures up to 1.1 GFa. Coupled charge density wave (CDW) tnul spin density wave (SDW) fluctuations were predicted as an origin of unusual properties of UGe2 by Watanabe and Miyake, but no additional superlttice Bragg peaks corresponding to the CDW reflections could be observed, resulting in an upper limit of its intensity of similar to 1 x 10(-4) to the fundamental Bragg peak intensity.

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  • Band gap closing in yttrium hydride at high prebures Reviewed

    Ayako Ohmura, Akihiko Machida, Tetsu Watanuki, Katsutoshi Aoki, Satoshi Nakano, K. Takemura

    Joint 20th AIRAPT and 43rd EHPRG International Conference on High Pressure Science and Technology   2005.1

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    High prebure infrared spectra were measured for yttrium trihydride, YH3, prepared by hydrogenation of yttrium metal in hydrogen fluid at prebures around 1 GPa. The spectral change with an hcp-fcc structural transition was observed at about 10 GPa in agreement with X-ray diffraction results. With further increase in prebure to 23 GPa, the hydride became opaque suddenly in the whole infrared region. X-ray diffraction measurement showed that the metal lattice maintained the fcc structure acrob the electronic transition likely with band gap closure. The 1s metal theoretically predicted was probably realized in YH3 at high prebures.

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  • Determination of low-pressure crystalline-liquid phase boundary of SnI4 Reviewed

    Kazuhiro Fuchizaki, Yasuhiko Fujii, Yasuo Ohishi, Ayako Ohmura, Nozomu Hamaya, Yoshinori Katayama, Taku Okada

    Journal of Chemical Physics   120 ( 23 )   11196 - 11199   2004.6

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    Using in situ x-ray diffraction measurements, the location of the liquidus in low-pressure crystalline-liquid phase boundary of Snl4 was investigated. The liquidus of low pressure crystalline phase of SnI4 was determined up to approximately 3.5 GPa. It was found that the liquidus is not well fitted to a monotonically increasing curve such as Simon's equation, but breaks near 1.5 GPa and then becomes flat. It was also found that the liquidus breaks near 1.5 GPa and becomes rather flat in the higher-pressure regime.

    DOI: 10.1063/1.1751397

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  • Structural analysis of a high-pressure amorphous phase of SnI4 Reviewed

    A. Ohmura, N. Hamaya, K. Sato, C. Ogawa, M. Isshiki, Y. Ohishi

    Journal of Physics Condensed Matter   14 ( 44 )   10553 - 10556   2002.11

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    We have performed a high-pressure synchrotron x-ray diffraction study of a metallic amorphous state in SnI4 induced by pressure. The Faber-Ziman structure factor S(Q) was obtained from diffraction intensities measured at pressures between 25 and 65 GPa. The first peak in S(Q) is relatively intense and sharp and the second peak is overlapped with the third one. Such features are also found in S(Q) for pure metallic glasses of Ni and Fe at 1 atm but not in molecular liquids. The obtained reduced radial distribution function g(r) shows no evidence for the presence of the SnI4 molecules in the metallic amorphous state.

    DOI: 10.1088/0953-8984/14/44/331

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  • 高圧力の科学・技術事典

    ( Role: Contributor)

    朝倉書店  2022.11  ( ISBN:9784254102970

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  • カルコパイライトCuFeS<sub>2</sub>におけるCuとFeの電子配置

    辻井直人, 山岡人志, 古江優作, 大村彩子, 石井啓文, 平岡望

    粉体粉末冶金協会講演大会(Web)   2021   2021

  • Study of Topological Quantum Materials under High-Pressure Reviewed

    Ayako OHMURA

    The Review of High Pressure Science and Technology   30 ( 4 )   281 - 289   2020

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    Publisher:The Japan Society of High Pressure Science and Technology  

    DOI: 10.4131/jshpreview.30.281

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  • 高圧下におけるSnI4固体のXAFS解析

    成田 博貴, 渕崎 員弘, 西村 光仙, 鈴木 昭夫, 大村 彩子, 若林 大佑

    日本物理学会講演概要集   74 ( 1 )   1712 - 1712   2019.3

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    DOI: 10.11316/jpsgaiyo.74.1.0_1712

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  • 小型静水圧セルの開発とYbCu<sub>x</sub>の物性測定

    古江優作, 大村彩子, 石川文洋, DE VISSER Anne, 辻井直人, 山岡人志

    高圧討論会講演要旨集   60th   2019

  • Bi<sub>50</sub>Sb<sub>50</sub>置換型合金における圧力誘起相分離

    大村彩子, 佐々木尚也, 古江優作, 中野智志, 石川文洋

    KEK Progress Report (Web)   ( 2019-7 )   2019

  • Investigation of topological phase transition in BiTeBr under high pressure

    A Ohmura, Y Higuchi, T Ochiai, M Kanou, S Nakano, F Ishikawa, A Nakayama, Yuh Yamada, T Sasagawa

    Journal of Physics: Conference Series   950   042036 - 042036   2017.10

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    The polar semiconductor BiTeBr has the P3m1 symmetry, similar to that of BiTeI, in which a pressure-induced topological phase transition from a trivial semiconductor to a topological insulator has been theoretically predicted. To investigate the topological phase transition in BiTeBr, we performed X-ray diffraction and electrical resistivity measurement under high pressure, and the band calculation using experimental structural parameters. The P3m1 structure is stable up to the pressure of similar to 7 GPa; the ratio of lattice constants (c/a) reaches a minimum at around 3 GPa. Furthermore, the following phenomena are observed at around this pressure; 1) the band-gap energy closes and reopens with pressure, 2) the temperature dependence of resistivity changes from metallic to semiconducting. From theoretical prediction in BiTeI, the topological phase transition is accompanied by the band gap closing/reopening. Therefore, the results obtained in BiTeBr suggest that the topological phase transition occurs at around 3 GPa.

    DOI: 10.1088/1742-6596/950/4/042036

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    Other Link: http://stacks.iop.org/1742-6596/950/i=4/a=042036?key=crossref.13518cb3dd7b6d7a487a8e1edb8a089d

  • 六方晶窒化ホウ素の各種圧媒体での加圧と構造および振動状態の圧力依存性

    中山敦子, 三谷翔平, 田口翔太郎, 梅津拓人, 星野豪, 佐藤貴明, 中野智志, 谷口尚, 大村彩子, 石川文洋, 山田裕

    高圧討論会講演要旨集   56th   2015

  • 9aPS-84 Transport properties of YBa_2Cu_4O_8 single crystal grown by KOH flux method

    Ishikawa F., Sawamura Naoko, Takahashi Hiroki, Nakayama A., Ohmura A., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   69 ( 2 )   422 - 422   2014.8

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  • 28aPS-104 Single crystal growth of Zn-substituted YBa_2Cu_4O_8 using KOH-NaOH flux

    Takahashi H., Sawamura N., Ishikawa F., Yamada Yuh, Nakayama A., Ohmura A.

    Meeting abstracts of the Physical Society of Japan   69 ( 1 )   617 - 617   2014.3

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  • 27pPSA-47 Substituted effect on conductivity on iron oxypnictide Sr_2CrFe_2As_2O_2

    Eguchi N., Wakabayashi T., Sanngu K., Hirata K., Yamagishi T., Ishikawa F., Ohmura A., Nakayama A., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   69 ( 1 )   574 - 574   2014.3

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  • 六方晶窒化ホウ素の水素中での加圧と圧力誘起構造相転移

    中山敦子, 田口翔太郎, 三谷翔平, 中野智志, 谷口尚, 大村彩子, 石川文洋, 山田裕

    高圧討論会講演要旨集   55th   2014

  • 高圧水素雰囲気下での六方晶窒化ホウ素の構造変化

    田口翔太郎, 中山敦子, 山田裕, 石川文洋, 大村彩子, 谷口尚, 中野智志

    物構研サイエンスフェスタ要旨集   2013   2014

  • 27pXZE-8 Synthesis of new series of Fe-oxypnictides with 21222 structure

    Ishikawa F., Eguchi N., Wakabayashi T., Hirata K., Kikuchi M., Sangu K., Kodama M., Nakayama A., Ohmura A., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   68 ( 1 )   663 - 663   2013.3

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  • 27pXZE-7 Synthesis of new iron-oxypnictide Sr_2CrFe_2As_2O_2 and its properties under high pressure

    Eguchi N., Wakabayashi T., Ishikawa F., Ohmura A., Nakayama A., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   68 ( 1 )   663 - 663   2013.3

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  • Pressure-induced phase-transition of cuprate superconductor YBa_2Cu_4O_8 : Crystal structure of high-pressure phase and its superconductivity Reviewed

    Atsuko Nakayama, Fumihiro Ishikawa, Keisuke Yuh, Yamada, Yusuke Onda, Shuhei Yamada, Hiroshi Fujihisa, Masafumi Sakata, Yuki Nakamoto, Katsuya Shimizu, Satoshi Nakano, Ayako Ohmura

    Meeting Abstracts of the Physical Society of Japan   68 ( 0 )   549 - 549   2013

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  • Phase transition and electrical resistivities of the cuprate with the CuO double chain under high pressure Reviewed

    Yuh Yamada, A. Ohmura, F.Ishikawa, R.Kobayashi, S.Yamada, A.Nakayama, U.Fujihisa, M.Sakata, Y.Nakamoto, K.Shimizu, S.Nakano

    Meeting Abstracts of the Physical Society of Japan   68 ( 0 )   510 - 510   2013

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  • 3GPa以下での水素中の六方晶窒化ホウ素の振動状態と構造の変化

    田口翔太郎, 中山敦子, 三谷翔平, 谷口尚, 中野智志, 大村彩子, 石川文洋, 山田裕

    物構研サイエンスフェスタ要旨集   1st   2013

  • 20pPSA-20 Investigation of superconductivity and crystal structure in Bi_<35>Te_<65> under high pressure

    Einaga M., Ohmura A., Ishikawa F., Nakayama A., Yamada Yuh, Nakano S.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   648 - 648   2012.8

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  • 20pPSB-32 Synthesis and properties of iron-based oxypnictide with blocking layers

    Eguchi N., Wakabayashi T., Ishikawa F., Ohmura A., Nakayama A., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   564 - 564   2012.8

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  • 20pPSA-19 Effect of pressure on the superconducting transition in Cu_<0.25>Bi_2(Te_xSe_<1-x>)_3

    Ohmura A., Matsuzawa M., Einaga M., Ishikawa F., Nakayama A., Yamada Yuh, Suzuki Y., Komatsu M., Kashiwagi T., Kadowaki K.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 )   647 - 647   2012.8

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  • 25aPS-134 Pressure-induced superconductivity in n-type Bi_2Te_3 with non-stoichiometric composition

    Einaga M., Ohmura A., Nakayama A., Ishikawa F., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   623 - 623   2012.3

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  • 27aCF-9 Pressure-induced phase-separation of graphite observed in MCMBs-H_2

    Isurugi Yuya, Nakayama Atsuko, Taguchi Shoutarou, Kiryuu Aoi, Nakano Satoshi, Ohmuram Ayako, Ishikawa Fumihiro, Yamada Yuh, Fujihisa Hiroshi

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   924 - 924   2012.3

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  • 25aPS-87 Synthesis and properties of Sr_4Cr_2Fe_2As_2O_6

    Ishikawa F., Kodama M., Watanabe T., Eguchi N., Nakayama A., Ohmura A., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   613 - 613   2012.3

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  • 25aPS-133 The relation between pressure-induced phase separation and superconducting transition temperature in bismuth-antimony alloy Bi_<1-x>Sb_x

    Ohmura A., Yamamura A., Einaga M., Nakayama A., Ishikawa F., Yamada Yuh, Nakano S.

    Meeting abstracts of the Physical Society of Japan   67 ( 1 )   623 - 623   2012.3

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  • 放射光X線回折によるテルル化ビスマスのbcc構造への圧力誘起相転移 Reviewed

    榮永茉利, 大村彩子, 中山敦子, 石川文洋, 山田裕, 中野智志

    Photon Factory News   29 ( 4 )   17   2012

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  • 高圧水素下における銀ろうの構造変化の観察

    田口翔太郎, 石動裕也, 中山敦子, 山田裕, 石川文洋, 大村彩子, 中野智志

    PFシンポジウム要旨集   29th   2012

  • 2GPa以下での水素中の六方晶窒化ホウ素の構造変化

    田口翔太郎, 副田大介, 中山敦子, 中野智志, 谷口尚, 大村彩子, 石川文洋, 山田裕

    高圧討論会講演要旨集   53rd   2012

  • 圧力を利用した炭素ナノ構造体の水素貯蔵に関する構造的研究

    石動裕也, 中山敦子, 田口翔太郎, 木竜葵, 中野智志, 大村彩子, 石川文洋, 山田裕, 藤久裕司

    PFシンポジウム要旨集   29th   2012

  • 21pRA-2 Magnetic properties of nonstoichiometric Fe_2VAl_<1+δ>

    Ishikawa F., Okawara Y., Nakayama A., Ohmura A., Yamada Yuh, Naka T., Matsushita A.

    Meeting abstracts of the Physical Society of Japan   66 ( 2 )   412 - 412   2011.8

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  • 22aPS-104 Pressure-induced superconductivity and structural phase transition in Bi_<1-x>Sb_x

    Ohmura A., Yamamura A., Einaga M., Nakayama A., Ishikawa F., Yamada Yuh, Nakano S.

    Meeting abstracts of the Physical Society of Japan   66 ( 2 )   532 - 532   2011.8

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  • 22aPS-105 Transport property in hexagonal Bi_2Te_3 under high pressure up to 8 GPa

    Einaga M., Ohmura A., Nakayama A., Ishikawa F., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   66 ( 2 )   533 - 533   2011.8

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  • 24aTE-10 Vibrational state of h-BN pressurized in a hydrogen atmosphere

    Nakayama Atsuko, Soeda Daisuke, Isurugi Yuya, Ohmura Ayako, Ishikawa Fumohiro, Yamada Yuh, Nakano Satoshi, Taniguchi Takashi

    Meeting abstracts of the Physical Society of Japan   66 ( 2 )   891 - 891   2011.8

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  • 25aHE-9 Magnetic properties of Fe_2VAl_<1+δ>

    Ishikawa F., Okawara Y., Nakayama A., Ohmura A., Yamada Yuh, Naka T., Matsushita A.

    Meeting abstracts of the Physical Society of Japan   66 ( 1 )   453 - 453   2011.3

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  • 26pPSA-49 Transport Property in Bi_2Te_3 and Bi_2Se_3 under High Pressure

    Einaga M., Ohmura A., Nakayama A., Ishikawa F., Yamada Yuh, Nakano S.

    Meeting abstracts of the Physical Society of Japan   66 ( 1 )   629 - 629   2011.3

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  • 26aEG-9 Pressure-induced superconductivity and structural phase transition in Bi_<1-x>Sb_x

    Ohmura A., Yamamura A., Einaga M., Nakayama A., Ishikawa F., Yamada Yuh, Nakano S.

    Meeting abstracts of the Physical Society of Japan   66 ( 1 )   818 - 818   2011.3

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  • 25aTB-2 Vibrational state of h-BN pressurized in a hydrogen atmosphere

    Nakayama Atsuko, Soeda Daisuke, Isurugi Yuya, Ohmura Ayako, Ishikawa Fumihiro, Yamada Yuh, Nakano Satoshi, Taniguchi Takashi

    Meeting abstracts of the Physical Society of Japan   66 ( 1 )   844 - 844   2011.3

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  • 25pPSB-56 Pressure effects on transport mechanism of ruprates with double chain

    Fujimaki Koji, Katoh Hiroki, Fukushima Seiya, Ishikawa Fumihiro, Ohmura Ayako, Nakayama Atsuko, Yamada Yuh, Takeshita Nao

    Meeting abstracts of the Physical Society of Japan   66 ( 1 )   577 - 577   2011.3

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  • 高圧水素雰囲気中で観察されるナノグラファイトの構造変化

    石動裕也, 田口翔太郎, 副田大介, 中山敦子, 中野智志, 大村彩子, 石川文洋, 山田裕, 藤久裕司

    高圧討論会講演要旨集   52nd   2011

  • 高圧水素中で観察されるhBNの振動状態

    中山敦子, 副田大介, 石動裕也, 田口翔太郎, 中野智志, 谷口尚, 大村彩子, 石川文洋, 山田裕

    高圧討論会講演要旨集   52nd   2011

  • Structure and superconductivity of Bi-Sb alloy under high pressure

    OHMURA Ayako, YAMAMURA Ayako, EINAGA Mari, NAKAYAMA Atsuko, ISHIKAWA Fumihiro, YAMADA Yuh, NAKANO Satoshi

    51   178 - 178   2010.10

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  • Development of the ultra-small high pressure cell using a technique of modified-Bridgman type anvils for magnetization measurements under high pressure

    ISHIKAWA Fumihiro, FUJIMAKI Koji, EINAGA Mari, OHMURA Ayako, NAKAYAMA Atsuko, YAMADA Yuh, MATSUSHITA Akiyuki, NAKA Takashi, NAKANISHI Takeshi

    51   278 - 278   2010.10

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  • Investigation of crystal structure and superconductivity in phase IV of Bi_2Te_3 under high pressure

    EINAGA Mari, ISHIKAWA Fumihiro, OHMURA Ayako, NAKAYAMA Atsuko, YAMADA Yuh, NAKANO Satoshi

    51   91 - 91   2010.10

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  • Crystal structure and properties of iron-pnictide BaFe_2As_2 under high pressure

    EGUCHI Naoya, KODAMA Michihiro, FUJIMAKI Koji, EINAGA Mari, ISHIKAWA Fumihiro, OHMURA Ayako, NAKAYAMA Atsuko, YAMADA Yuh, NAKANO Satoshi

    51   207 - 207   2010.10

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  • 25pPSA-9 Electrical transport and magnetic property of Fe_2VAl_<1±δ>(δ≦0.04) Heusler alloy

    Ohkawara Y., Eguchi N., Kodama M., Fujimaki K., Ishikawa F., Yamada Yuh, Nakayama A., Ohmura A.

    Meeting abstracts of the Physical Society of Japan   65 ( 2 )   431 - 431   2010.8

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  • 23aPS-30 Oxygen compositon dependence of electronic transport property in Pr_2Ba_4Cu_7O_<15-δ>

    Fukushima S., Fujimaki K., Yamada S., Ishikawa F., Ohmura A., Nakayama A., Yamada Yuh, Matsushita A.

    Meeting abstracts of the Physical Society of Japan   65 ( 2 )   466 - 466   2010.8

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  • 23aPS-134 Effect of Sb doping level and pressure on the electrical resistivity of Bi_<1-x>Sb_x(x<0.22)

    Yamamura A., Ohmura A., Einaga M., Nakayama A., Ishikawa F., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   65 ( 2 )   491 - 491   2010.8

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  • 20pPSB-8 Crystal structure of BaFe_2As_2 under high-pressure

    Eguchi N., Kodama M., Fujimaki K., Einaga M., Ishikawa F., Ohmura A., Nakayama A., Yamada Yuh, Mitsuda A., Nakano S.

    Meeting abstracts of the Physical Society of Japan   65 ( 1 )   578 - 578   2010.3

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  • 21aGR-1 Equation of state for solid neon at ultrahigh pressures

    Takemura K., Watanuki T., Ohwada K., Machida A., Ohmura A., Aoki K.

    Meeting abstracts of the Physical Society of Japan   65 ( 1 )   869 - 869   2010.3

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  • 20aPS-108 Pressure effect of superconductivity and crystal structure in Bi_<1-x>Sb_x

    Ohmura A., Yamamura A., Tanabe Y., Einaga M., Nakayama A., Ishikawa F., Yamada Yuh, Nakano S.

    Meeting abstracts of the Physical Society of Japan   65 ( 1 )   545 - 545   2010.3

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  • 20pPSA-15 Synthesis of single crystalline sample Pr_2Ba_4Cu_7O_<15-δ>

    Kato H., Fukushima S., Onda Y., Ishikawa F., Yamada Y., Ohmura A., Nakayama A., Matsushita A., Horii S.

    Meeting abstracts of the Physical Society of Japan   65 ( 1 )   568 - 568   2010.3

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  • 20pHY-14 Pressure-induced superconductivity and structural phase transition in Bi_2Te_3

    Einaga M., Nakayama A., Ohmura A., Ishikawa F., Yamada Yuh, Nakano S.

    Meeting abstracts of the Physical Society of Japan   65 ( 1 )   821 - 821   2010.3

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  • 23pGH-5 Anisotropic pressure effects on pressure-induced superconductivity in BaFe_2As_2

    Ishikawa F., Eguchi N., Kodama M., Fujimaki K., Einaga M., Nakayama A., Ohmura A., Matoba T., Mitsuda A., Wada Hirofumi, Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   65 ( 1 )   686 - 686   2010.3

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  • 26pYA-13 Structure and electrical property of Bi_<1-x>Sb_x under high pressure

    Ohmura A., Tanabe Y., Einaga M., Ishikawa F., Nakayama A., Yamada Yuh, Nakano S.

    Meeting abstracts of the Physical Society of Japan   64 ( 2 )   707 - 707   2009.8

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  • 26aPS-113 High-pressure studies on structure and properties of iron arsenide BaFe_2As_2 produced by high-pressure synthesis

    Eguchi N., Kodama M., Fujimaki K., Einaga M., Ishikawa F., Ohmura A., Nakayama A., Yamada Yuh, Mitsuda A., Nakano S.

    Meeting abstracts of the Physical Society of Japan   64 ( 2 )   503 - 503   2009.8

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  • 26aPS-110 High-pressure synthesis and properties of iron-based oxypnictide superconductor

    Kodama M., Eguchi N., Fujimaki K., Einaga M., Ohmura A., Ishikawa F., Nakayama A., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   64 ( 2 )   502 - 502   2009.8

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  • 28aRH-4 Pressure-induced superconductivity in BaFe_2As_2

    Ishikawa F., Eguchi N., Kodama M., Fujimaki K., Einaga M., Nakayama A., Ohmura A., Mitsuda A., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   64 ( 2 )   560 - 560   2009.8

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  • 25aPS-120 Investigation of the superconductivity in crystalline phase III of Bi_2Te_3 under high pressure

    Einaga M., Nakayama A., Ohmura A., Ishikawa F., Yamada Yuh, Nakano S.

    Meeting abstracts of the Physical Society of Japan   64 ( 2 )   443 - 443   2009.8

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  • 26aPS-20 Pressure-induced structural-phase trandsition of YBa_2Cu_4O_8

    Onda Y., Hiura Y., Nakayama A., Ishikawa F., Ohmura A., Yamada Yuh, Nakano S., Matsushita A.

    Meeting abstracts of the Physical Society of Japan   64 ( 2 )   482 - 482   2009.8

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  • 27pTH-9 Anisotropic transport properties of Fe_2VAl Heusler alloy

    Ishikawa F., Hirota S., Ohmura A., Nakayama A., Yamada Yuh, Matsushita A.

    Meeting abstracts of the Physical Society of Japan   64 ( 1 )   459 - 459   2009.3

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  • 28aPS-30 Pressure dependence of superconducting transition temperature in YbGa_<1.1>Si_<0.9>

    Ohmura A., Fujimaki K., Einaga M., Ishikawa F., Nakayama A., Yamada Yuh, Imai M., Tsujii N.

    Meeting abstracts of the Physical Society of Japan   64 ( 1 )   602 - 602   2009.3

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  • 28aPS-37 Pressure-induced structural change in the Bi_<1-x>Sb_x alloys

    Tanabe Y., Einaga M., Nakayama A., Ohmura A., Ishikawa F., Yamada Yuh, Nakano S.

    Meeting abstracts of the Physical Society of Japan   64 ( 1 )   604 - 604   2009.3

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  • YbGa<sub>1.1</sub>Si<sub>0.9</sub>の超伝導転移温度の圧力効果

    大村彩子, 藤巻孔二, 榮永茉利, 石川文洋, 中山敦子, 山田裕, 今井基晴, 辻井直人

    日本物理学会講演概要集   64 ( 1 )   2009

  • 22aPS-99 The rare earth dependence of photocatalytic activities on Ba_2RBiO_6 (R=rare earth) oxide

    Hatakeyama T., Takeda S., Ishikawa F., Ohmura A., Nakayama A., Yamada Yuh, Matsushita A., Ye Jinhua

    Meeting abstracts of the Physical Society of Japan   63 ( 2 )   673 - 673   2008.8

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  • 21pPSA-35 Transport properties of Fe_2VAl_<1+δ> single crystal under high pressure

    Hirota S., Tanabe Y., Ishikawa F., Nakayama A., Ohmura A., Yamada Yuh, Matsushita A.

    Meeting abstracts of the Physical Society of Japan   63 ( 2 )   393 - 393   2008.8

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  • 23pVE-9 High pressure Raman and UV-vis. spectra of Sc hydride

    Kume T., Takeichi T., Sasaki S., Shimizu H., Machida A., Watanuki T., Aoki K., Ohmura A., Takemura K.

    Meeting abstracts of the Physical Society of Japan   63 ( 2 )   895 - 895   2008.8

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  • 20pPSB-31 Synthesis and superconducting properties of MoSr_2YCu_2O_<8-δ> system under high pressure

    Fujimaki K., Udagawa K., Ishikawa F., Ohmura A., Nakayama A., Yamada Yuh

    Meeting abstracts of the Physical Society of Japan   63 ( 2 )   477 - 477   2008.8

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  • 20pPSB-29 Magnetic properties of Pr_2Ba_4Cu_7O_<15-δ> oxide superconductor under high pressure

    Onda Y., Hiura Y., Ishikawa F., Ohmura A., Nakayama A., Yamada Yuh, Matsushita A.

    Meeting abstracts of the Physical Society of Japan   63 ( 2 )   476 - 476   2008.8

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  • 20pPSB-30 Pressure dependence of crystal structure and electrical conduction on Pr_2Ba_4Cu_7O_<15-δ>

    Hiura Y., Onda Y., Einaga M., Nakayama A., Ishikawa F., Ohmura A., Yamada Yuh, Kagayama T., Nakano S., Matsushita A.

    Meeting abstracts of the Physical Society of Japan   63 ( 2 )   477 - 477   2008.8

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  • エネルギー利用を目指した水素化物の材料設計

    池田一貴, 李海文, 大村彩子, 松尾元彰, 佐藤豊人, 中森裕子, 折茂慎一

    高圧力の科学と技術   18 ( 2 )   180 - 185   2008.5

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    Energy-related materials are expected to reinforce energy security and solve worldwide environmental problems. We are currently focusing on the developments of advanced hydrogen storage materials for fuel cell technologies. Actually we have studied new metal-, complex- and perovskite-hydrides composed of light elements using high pressure technique and microwave process. In addition, hydrides researches connected with secondary battery and neutron shield have being also progressed, aiming at searching new functional materials. In this article, we introduce our recent studies of various hydrides for energy-related applications.

    DOI: 10.4131/jshpreview.18.180

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  • Frontier of high pressure research on metal hydrides Reviewed

    Katsutoshi Aoki, Akihiko Machida, Ayako Ohmura, Tetsu Watanuki

    Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu   18 ( 3 )   273 - 278   2008

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    The highly compressed state of metal hydride has been investigated to explore structural and electronic transitions characteristic to hydride. The hydrogen atoms play the lead in the transitions, showing displacement in or transfer between the interstitial sites of a metal lattice. One example is the band gap closing observed for a long period lattice of yttrium tri-hydride, YH3, appearing at pressures above 12 GPa. Another example is photochromic event observed again for yttrium hydride, YHx. The former is likely accompanied by the in-site displacement of hydrogen atoms and the latter by the site-to-site transfer.

    DOI: 10.4131/jshpreview.18.273

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  • 24aTD-7 Pressure induced disproportionation in rare-earth metal dihydrides

    Machida A., Ohmura A., Watanuki T., Aoki K.

    Meeting abstracts of the Physical Society of Japan   62 ( 2 )   1013 - 1013   2007.8

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  • Long-period stacking structures in yttrium trihydride at high pressure Reviewed

    A. Machida, A. Ohmura, T. Watanuki, K. Aoki, K. Takemura

    PHYSICAL REVIEW B   76 ( 5 )   2007.8

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    The pressure-induced structural transition of YH3 has been investigated by x-ray diffraction experiments under hydrostatic pressure at room temperature. The diffraction patterns of the intermediate state between the hexagonal and cubic phases are interpreted in terms of long-period polytypes with the periodic arrangements of hexagonal-type and fcc-type stacking layers of the Y metals. The hydrogen-hydrogen repulsive interactions and hydrogen-metal bonding likely play a dominant role in the gradual hexagonal-fcc lattice conversion via the long-period polytypic structures.

    DOI: 10.1103/PhysRevB.76.052101

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  • 20pXB-9 Structural transition process in yttrium trihydride under high pressure

    Machida A., Ohmura A., Watanuki T., Aoki K., Takemura K.

    Meeting abstracts of the Physical Society of Japan   62 ( 1 )   975 - 975   2007.2

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  • 24aZD-2 Pressure dependence of the infrared spectra of scandium hydride ScH_x

    Omura Ayako, Machida Akihiko, Watanuki Tetsu, Aoki Katsutoshi, Takemura K.

    Meeting abstracts of the Physical Society of Japan   61 ( 2 )   790 - 790   2006.8

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  • 25pYK-17 Raman and visible absorption spectra of YH_3 under high pressure

    Kume T., Ohura H., Sasaki S., Shimizu H., Ohmura A., Machida A., Watanuki T., Aoki K., Takemura K.

    Meeting abstracts of the Physical Society of Japan   61 ( 2 )   808 - 808   2006.8

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  • 25pYK-16 Structural transition in yttrium trihydride under high pressure

    Machida A., Ohmura A., Watanuki T., Aoki K., Takemura K.

    Meeting abstracts of the Physical Society of Japan   61 ( 2 )   808 - 808   2006.8

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  • 28pXE-9 Structural deformation of Cd-Yb quasicrystal under high pressure and low temperature

    Watanuki T., Machida A., Ohmura A., Aoki K., Ohwada K., Sato T.J., Tsai A.P.

    Meeting abstracts of the Physical Society of Japan   61 ( 1 )   778 - 778   2006.3

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  • 27pXD-8 High pressure infrared spectroscopy of scandium hydride

    Omura Ayako, Machida Akihiko, Watanuki Tetsu, Aoki Katsutoshi, Takemura K.

    Meeting abstracts of the Physical Society of Japan   61 ( 1 )   926 - 926   2006.3

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  • 27pXD-7 Structural transition in lanthanum hydride under high pressure

    Machida A., Ohmura A., Watanuki T., Aoki K., Takemura K.

    Meeting abstracts of the Physical Society of Japan   61 ( 1 )   926 - 926   2006.3

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  • Infrared spectroscopic study of the band-gap closure in YH3 at high pressure

    A Ohmura, A Machida, T Watanuki, K Aoki, S Nakano, K Takemura

    PHYSICAL REVIEW B   73 ( 10 )   2006.3

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    Infrared vibrational absorption spectra are measured for yttrium trihydride at room temperature and pressures up to 30 GPa. The spectral change that begins near 12 GPa is interpreted in terms of a hcp-fcc structural transition, which agrees with previous x-ray diffraction measurements. For the hydrogen vibrations in the low-pressure hcp phase, the mode Gruneisen parameters are derived from the observed peak frequency shifts with pressure and the reported bulk modulus. The value of 1.91 for the octahedral-site vibration is three times larger than those for the tetrahedral-site vibrations, suggesting hybridization between the hydrogen 1s and yttrium 4d orbitals at the octahedral site. The infrared transmission spectra collapse when the high-pressure fcc phase is compressed beyond 23 GPa. The band gap abruptly closes without a structural change in the fcc metal lattice. The experimental results are in contrast to the previous theoretical calculations predicting the electronic transition either with hcp-fcc structural change or in the hcp low-pressure phase without structural change. The transition mechanism is still inconclusive.

    DOI: 10.1103/PhysRevB.73.104105

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  • 希土類金属水素化物の高圧下の構造・電子転移 Reviewed

    青木勝敏, 綿貫徹, 町田晃彦, 大村彩子

    固体物理   41 ( 11 )   780   2006

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  • 21aYE-8 Structural and electronic transition in rare-earth metal hydrides under high pressure

    Machida A., Ohmura A., Watanuki T., Aoki K., Nakano S., Takemura K.

    Meeting abstracts of the Physical Society of Japan   60 ( 2 )   818 - 818   2005.8

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  • 21aYE-7 Pressure-induced structural changes of scandium hydride

    Ohmura Ayako, Machida Akihiko, Watanuki Tetsu, Aoki Katsutoshi, Nakano Satoshi, Takemura K.

    Meeting abstracts of the Physical Society of Japan   60 ( 2 )   818 - 818   2005.8

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  • 20pYK-12 Structural deformation of Cd-Yb quasicrystal under hydrostatic pressure.

    Watanuki T., Machida A., Ohmura A., Aoki K., Ohwada K., Sato T. J., Tsai A. P.

    Meeting abstracts of the Physical Society of Japan   60 ( 2 )   648 - 648   2005.8

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  • 27aYQ-8Structural deformation of Cd-Yb quasicrystal under hydrostatic pressure.

    Watanuki T., Machida A., Ohmura A., Aoki K., Ohwada K., Sato T.J., Tsai A.P.

    Meeting abstracts of the Physical Society of Japan   60 ( 1 )   761 - 761   2005.3

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  • 25aYM-3 Pressure dependence of the infrared spectra of metallic hydride YH_x

    Ohmura Ayako, Machida Akihiko, Watanuki Tetsu, Aoki Katsutoshi, Nakano Satoshi, Takemura Kenichi

    Meeting abstracts of the Physical Society of Japan   60 ( 1 )   902 - 902   2005.3

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  • 14pTJ-8 High-pressure synthesis and structural properties of La- and Y-hydride

    Machida A., Watanuki T., Ohmura A., Aoki K., Nakano S., Takemura K.

    Meeting abstracts of the Physical Society of Japan   59 ( 2 )   878 - 878   2004.8

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  • Phase boundary between low-pressure crystalline state of molecular crystal SnI_4 and liquid state under hydrostatic pressure II

    FUCHIZAKI K., OHMURA A., HAMAYA N., NAGAI K., OHISHI Y., KATAYAMA Y., FUJII Y.

    Meeting abstracts of the Physical Society of Japan   58 ( 2 )   749 - 749   2003.8

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Presentations

  • Evidence substantiating the existence of the liquid-liquid critical point in tin tetraiodide

    Fuchizaki Kazuhiro, Ohmura Ayako, Suzuki Akio, Nishida Keisuke, Hamaya Nozomu, Saitoh Hiroyuki

    Meeting Abstracts of the Physical Society of Japan  2016  The Physical Society of Japan

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  • Evidence substantiating the existence of the temperatures of maximum density in tin tetraiodide

    Fuchizaki Kazuhiro, Ohmura Ayako, Suzuki Akio, Nishida Keisuke, Hamaya Nozomu, Saitoh Hiroyuki

    Meeting Abstracts of the Physical Society of Japan  2016  The Physical Society of Japan

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  • Investigation of pressure-induced superconducting transition in BiTeCl (II)

    Ohmura A., Kawabe T., Yoshihara K., Ishikawa F., Kanou M., Nakayama A., Yamada Yuh, Sasagawa T.

    Meeting Abstracts of the Physical Society of Japan  2016  The Physical Society of Japan

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    Event date: 2016

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  • 24aPS-25 Effect on superconducting properties of synthesis conduction in cuprate superconductor Pr_2Ba_4Cu_7O_<15-δ>

    Hyodo S., Inaba K., Ohashi K., Ishikawa F., Nakayama A., Ohmura A., Yamada Yuh

    Meeting Abstracts of the Physical Society of Japan  2015  The Physical Society of Japan (JPS)

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  • 24aPS-60 Pressure effects on transport properties of BaFe_2As_2 under hydrostatic pressure

    Hirata K., Eguchi N., Sangu K., Yamagishi T., Ishikawa F., Nakayama A., Ohmura A., Yamada Yuh

    Meeting Abstracts of the Physical Society of Japan  2015  The Physical Society of Japan (JPS)

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  • 24aPS-61 Transport properties of K(Fe_<1-x>Co_x)_2As_2 under high pressure

    Sangu K., Eguchi N., Hirata K., Yamagishi T., Okaji R., Ishikawa F., Nakayama A., Ohmura A., Yamada Yuh

    Meeting Abstracts of the Physical Society of Japan  2015  The Physical Society of Japan (JPS)

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Awards

  • フロンティア材料研究所学術賞(研究奨励部門)

    2017.5   東京工業大学  

    大村 彩子

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Research Projects

  • CdI2型遷移金属ダイテルライドにおけるバルク・表面超伝導の探索と高圧物性研究

    Grant number:24K06937

    2024.4 - 2027.3

    System name:科学研究費助成事業

    Research category:基盤研究(C)

    Awarding organization:日本学術振興会

    大村 彩子

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    Grant amount:\4550000 ( Direct Cost: \3500000 、 Indirect Cost:\1050000 )

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  • ディラック半金属PdTe2における圧力誘起トポロジカル相転移と超伝導特性

    Grant number:20H01851

    2020.4 - 2024.3

    System name:科学研究費助成事業 基盤研究(B)

    Research category:基盤研究(B)

    Awarding organization:日本学術振興会

    大村 彩子

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    Authorship:Principal investigator 

    Grant amount:\17550000 ( Direct Cost: \13500000 、 Indirect Cost:\4050000 )

    本研究の目的は、非自明な表面状態をもつタイプII型ディラック半金属PdTe2において5 GPa付近で理論予測された圧力誘起トポロジカル相転移(リフシッツ転移)と超伝導特性の関係を実験的に解明すること、さらに表面超伝導が磁場下で示す異常な振る舞いの起源を解明してPdTe2のトポロジカル超伝導の可能性を検証することである。初年度に得られた成果は下記の通りである。
    1. 申請時点で超伝導転移温度(Tc)の圧力依存性が5 GPa付近で極大をもつことを見出しており,トポロジカル相転移との関係性が期待された。しかし,その後の二度の再測定ではTc極大の再現性は得られず,いずれも1 GPa以上の圧力域においてTc値は単調に減少した。再現性が得られた結果(1 GPa以上での単調減少)がPdTe2の本質的であると結論付け,少なくとも電気抵抗測定では相転移を示唆する変化は検出されないことがわかった。5 GPa付近の極大については,その発現圧力およびTc値から構成元素であるTeによる圧力誘起超伝導であると推測された。
    2. 初年度は,2種の圧力媒体を用いて10 GPa以下の圧力域で静水圧下X線回折を実施し,低圧域での詳細な圧力変化を観測した。PdTe2の高圧下構造については特に低圧域の情報が不足していたため,本研究で得たデータは物性測定を考察する上で重要な結果となりうる。
    3. 表面超伝導の評価に向けて,表面敏感な測定法と高圧発生技術を組み合わせた新規測定法の確立を目指しており,初年度は第一段階として,1)高圧セルの試料室周辺部の最適化と2)標準的な超伝導試料(常圧試料)を用いた計測系の構築を並行して進めた。その結果,1)では高圧力発生の点での構成部材の最適化はほぼ完了した。しかし,信号検出という点では,1)と2)どちらにおいても改善が必要であることが判明し,次年度以降の課題となった。

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  • ディラック半金属超伝導体の物性解明

    2019.6 - 2020.3

    System name:試験研究費助成

    Awarding organization:公益財団法人内田エネルギー科学振興財団

    大村 彩子

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  • Investigation of the origin of highly anomalous valence change in Yb compounds

    Grant number:18K18743

    2018.6 - 2023.3

    System name:Grants-in-Aid for Scientific Research

    Research category:Grant-in-Aid for Challenging Research (Exploratory)

    Awarding organization:Japan Society for the Promotion of Science

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    Grant amount:\6240000 ( Direct Cost: \4800000 、 Indirect Cost:\1440000 )

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  • Bi系層状ラシュバ物質群における圧力誘起超伝導および構造相転移の研究

    2016.4 - 2019.3

    System name:科学研究費補助金 基盤研究(C)

    Awarding organization:日本学術振興会

    大村 彩子

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  • 環境低負荷型電子デバイスへの応用に向けたビスマス系新奇超伝導材料の基礎物性研究

    2014 - 2015

    System name:試験研究費助成

    Awarding organization:一般財団法人佐々木環境技術振興財団

    大村 彩子

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  • 多重極限下の電子・熱物性測定と結晶構造解析による圧力誘起トポロジカル超伝導の研究

    2013.4 - 2015.3

    System name:科学研究費補助金 新学術領域研究「対称性の破れた凝縮系におけるトポロジカル量子現象」

    Awarding organization:文部科学省

    大村 彩子

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  • 電子輸送特性と結晶構造の低温高圧下同時測定によるビスマス系化合物の超伝導の研究

    2012.4 - 2014.3

    System name:科学研究費補助金 若手研究(B)

    Awarding organization:日本学術振興会

    大村 彩子

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  • 高圧力下熱電能測定装置の開発とBi系合金における高圧下電子状態に関する研究

    2010

    System name:育英奨学会研究助成

    Awarding organization:公益財団法人ユニオンツール

    大村 彩子

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  • フラストレート系CuOジグザグチェーンにおける超伝導の研究

    Grant number:20046006

    2008 - 2009

    System name:科学研究費助成事業

    Research category:特定領域研究

    Awarding organization:日本学術振興会

    山田 裕, 中山 敦子, 石川 文洋, 大村 彩子

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    Grant amount:\3700000 ( Direct Cost: \3700000 )

    我々は、最近Pr_2Ba_4Cu_7O_<15・δ>(Pr247)酸化物において酸素還元処理を施すことにより超伝導がTc=15K付近で出現することを発見した。これは従来のCuO_2二次元面による超伝導とは異なりCuOジグザグチェーンにおける超伝導であると考えられる。この超伝導の発見は銅系酸化物超伝導体における全く新しい超伝導の出現となるばかりでなく、その結晶構造から、擬一次元伝導機構による初めての超伝導物質であると考えられる。CuOジグザグチェーンは元来フラストレーションスピン系にキャリアーをドープした系である。事実、キャリアー依存性、圧力依存性で様々な量子相が観測されている。そこで我々はこのCuOジグザグチェーンチェーンのキャリア数を制御して、電子輸送特性及び結晶構造解析を調べることによりその物性を解明することを試みた。
    本年度は特に10GPaを超える高圧力下での物性及び結晶構造を明らかにした。その結果、CuOジグザグチェーンを有するY124, Y247, Pr124, Pr247のすべてが10GPa以上で構造相転移を起こすことが確認できた。これはCuOジグザグチェーンを持たないPr123構造では起こらないことからCuOジグザグチェーンが壊れている可能性が高いことが示唆された。さらに電気抵抗の測定により10GPa以上で電気抵抗が急激に減少することから、構造相転移により新しい伝導面が形成された可能性が示唆された。

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  • 圧力を用いた炭素π電子系配列ナノ空間の水素吸蔵についての研究

    Grant number:20045003

    2008 - 2009

    System name:科学研究費助成事業

    Research category:特定領域研究

    Awarding organization:日本学術振興会

    中山 敦子, 山田 裕, 石川 文洋, 大村 彩子

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    Grant amount:\5000000 ( Direct Cost: \5000000 )

    ナノグラファイト構造をもつ炭素π電子系配列ナノ空間物質は、高圧下で水素(H_2)を吸蔵する。このとき、H_2との間に大きな電気的相互作用が働くことによって、0.7GPa以下では、ハニカム格子を等方的に伸ばすことがこれまでの研究で自明である。この現象を理解し、H_2が炭素π電子系配列ナノ空間の何処にどのような状態で存在するか明らかにするために、メソカーボンマイクロビーズ(MCMB)の高圧H_2およびヘリウム(He)中でのラマンスペクトルを観察した。先に1GPa以下で観察したX線回折の結果を含め、全体を次のように考察した。
    1GPa以下で観察されるMCMBs-H_2とMCMBs-HeのG-bandの圧力変化は、大きく異なる。0.7GPa以下では相反する現象:「ハニカム格子の伸び」と「G-bandのハード化」が同時に起こる。これには、C=C結合の振動を抑制するH_2の配向を考慮する必要がある。ハニカム格子を伸ばすには、Cのπ軌道とHのs軌道の重なりによる電荷移動が必要で、H_2はグラフェンに垂直に配位しなければならない。しかし、層間距離は圧縮されるため、H_2が層間に縦配向することは考えにくい。「グラフェン面へのH_2の串刺し構造」であれば、層間距離が伸びることなくハニカム格子が伸び、しかも、格子振動が固くなる。また、H_2の配向が変化し、ハニカム格子に対して垂直でなくなれば、電気的な相互作用が弱くなり、一時的に格子振動がソフト化しつつ格子が縮むことから、このモデルが妥当であると考える。結論すると、0.7GPa以下では、H_2の層間へのインターカレーションを、また、0.7GPa≦P≦1GPaでは、H_2のハニカム格子に対する配向の変化を示唆する。

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  • 20 GPa超級改良型ブリッジマンアンビルセルの開発とシリコンの圧力誘起金属相における超伝導特性の探索に関する研究

    2008

    System name:育英奨学会研究助成

    Awarding organization:公益財団法人ユニオンツール

    大村 彩子

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  • 磁気天秤を用いた5GPa級高圧下精密帯磁率測定装置の開発

    Grant number:19654050

    2007 - 2008

    System name:科学研究費助成事業

    Research category:萌芽研究

    Awarding organization:日本学術振興会

    山田 裕, 石川 文洋, 大村 彩子, 中西 剛司, 名嘉 節

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    Grant amount:\3300000 ( Direct Cost: \3300000 )

    我々はこれまで超伝導と強磁性が共存するRuSr2GdCu2O8 (Ru1212)酸化物超伝導体あるいは超伝導と反強磁性が共存するMoSr2YCu2O8 (Mo1212)酸化物超伝導体についてその高圧下での物性測定を行ってきた。特にMo1212酸化物超伝導体は、圧力を加えることにより超伝導遷移温度Tcは当初7K/GPaという非常に大きな割合で上昇し、10GPa下でもまだ上昇を続けることが分かった。この機構を明らかにするには共存する磁気秩序(反強磁性)の圧力依存性を高い圧力で精度良く調べることが必要不可欠となった。しかしながらこのような装置は世界中どこにも存在しない。そこで本研究では5GPaを超える高い圧力下において高精度で磁化の温度依存性が測定可能な装置の開発を行うことを目的としている。本年度は硬質プラスチック(PBI)を用いたブリッジマンアンビルセルのクランプ強度試験とジルコニア製のアンビルによる発生圧力試験を行った。設計及び製作を行なった。硬質プラスチック(PBI)の強度計算より算出していたクランプ重量は2トンであったが、実際に荷重をかけたところ2トンクランプすると課題の部分が破壊し、その強度に問題を残す結果となった。一方ジルコニア製のアンビルによる発生加圧試験では、Biの電気抵抗測定により調べたところ、2トンでI-IIの構造相転移に対応する電気抵抗の減少が観測できた。このことから2トンで2GPaを超える圧力が出ていると予想される。以上の結果より高い圧力を発生させるためにはPBIの強度にやや問題があり今後他の硬質プラスチック及びジュラルミン等、非磁性で軽量・強高度の材料を試す必要がある。
    現在既に軽量化した銅ベリルウムセル及びセラミックセルの設計を行っており5GPa級圧力セルの開発は可能であると確信している。

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Teaching Experience

  • 物理学概論

    2023
    Institution name:新潟大学

  • 量子研究の最前線

    2023
    Institution name:新潟大学

  • 理学基礎演習

    2022
    Institution name:新潟大学

  • 固体物性物理学I

    2022
    Institution name:新潟大学

  • 不規則系物理学II

    2022
    Institution name:新潟大学

  • 理学スタディ・スキルズ

    2022
    Institution name:新潟大学

  • 電磁気学IIA

    2021
    Institution name:新潟大学

  • 電磁気学IIB

    2021
    Institution name:新潟大学

  • 課題研究A

    2021
    Institution name:新潟大学

  • 課題研究B

    2021
    Institution name:新潟大学

  • 課題研究D

    2021
    Institution name:新潟大学

  • 課題研究C

    2021
    Institution name:新潟大学

  • 自然科学基礎実験

    2021
    Institution name:新潟大学

  • 先端科学技術総論

    2021
    Institution name:新潟大学

  • 現代物理学セミナーB

    2020
    Institution name:新潟大学

  • 現代物理学セミナーA

    2020
    Institution name:新潟大学

  • 専門力アクティブ・ラーニング

    2020
    -
    2021
    Institution name:新潟大学

  • 固体物性物理学Ⅰ

    2020
    Institution name:新潟大学

  • 安全教育

    2020
    Institution name:新潟大学

  • 物性物理学

    2019
    Institution name:新潟大学

  • 理学スタディ・スキルズ

    2019
    -
    2022
    Institution name:新潟大学

  • 物理学基礎実習a

    2018
    -
    2022
    Institution name:新潟大学

  • 物理学基礎実習b

    2018
    -
    2022
    Institution name:新潟大学

  • 物理学基礎ゼミ

    2018
    Institution name:新潟大学

  • 物理学実験B

    2017
    Institution name:新潟大学

  • 物理学実験A

    2017
    Institution name:新潟大学

  • 物理学実験C

    2017
    Institution name:新潟大学

  • 物理学実験D

    2017
    -
    2022
    Institution name:新潟大学

  • 物性物理学II

    2017
    -
    2020
    Institution name:新潟大学

  • 電磁気学a

    2015
    -
    2016
    Institution name:新潟大学

  • 現代物理学への招待(物理学学習法)

    2014
    -
    2020
    Institution name:新潟大学

  • 物性物理学I

    2014
    -
    2015
    Institution name:新潟大学

  • 物理学実験a

    2009
    -
    2016
    Institution name:新潟大学

  • 物理学実験b

    2009
    -
    2016
    Institution name:新潟大学

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Social Activities

  • 令和元年度日本物理教育学会新潟支部クリスマス講演会

    Role(s): Lecturer

    2019.12

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  • 令和元年度新潟県高校生理数トップセミナー・グループ研究(物理テーマ)担当

    Role(s): Lecturer

    2019.11 - 2019.12

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  • 新潟ジュニアドクター育成塾

    2019.9 - 2024.2

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  • 青少年のための科学の祭典

    Role(s): Demonstrator

    2009.11

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