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Cao, Y.*; Zhou, H.*; Khmelevskyi, S.*; Lin, K.*; Avdeev, M.*; Wang, C.-W.*; Wang, B.*; Hu, F.*; Kato, Kenichi*; Hattori, Takanori; et al.
Chemistry of Materials, 35(8), p.3249 - 3255, 2023/04
Times Cited Count:0 Percentile:0(Chemistry, Physical)Hydrostatic and chemical pressure are efficient stimuli to alter the crystal structure and are commonly used for tuning electronic and magnetic properties in materials science. However, chemical pressure is difficult to quantify and a clear correspondence between these two types of pressure is still lacking. Here, we study intermetallic candidates for a permanent magnet with a negative thermal expansion (NTE). Based on in situ synchrotron X-ray diffraction, negative chemical pressure is revealed in HoFe on Al doping and quantitatively evaluated by using temperature and pressure dependence of unit cell volume. A combination of magnetization and neutron diffraction measurements also allowed one to compare the effect of chemical pressure on magnetic ordering with that of hydrostatic pressure. Intriguingly, pressure can be used to control suppression and enhancement of NTE. Electronic structure calculations indicate that pressure affected the top of the majority band with respect to the Fermi level, which has implications for the magnetic stability, which in turn plays a critical role in modulating magnetism and NTE. This work presents a good example of understanding the effect of pressure and utilizing it to control properties of functional materials.
Ishii, Yui*; Yamamoto, Arisa*; Sato, Naoki*; Nambu, Yusuke*; Kawamura, Seiko; Murai, Naoki; Ohara, Koji*; Kawaguchi, Shogo*; Mori, Takao*; Mori, Shigeo*
Physical Review B, 106(13), p.134111_1 - 134111_7, 2022/10
Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)Matsuura, Masato*; Fujiwara, Yasuyuki*; Moriwake, Hiroki*; Ohara, Koji*; Kawakita, Yukinobu
Physical Review B, 104(9), p.094305_1 - 094305_7, 2021/09
Times Cited Count:4 Percentile:46.2(Materials Science, Multidisciplinary)Yoneda, Yasuhiro; Ohara, Koji*
Fummatsu X-sen Kaiseki No Jissai, Dai-3-Han, p.272 - 286, 2021/08
In recent material development, not only conventional crystal structure analysis but also pair distribution function (PDF) analysis is increasingly used. This chapter (Chapter 15) deals with PDF analysis of crystalline materials using data obtained from synchrotron radiation powder X-ray diffraction experiments.
Fukuda, Tatsuya*; Takahashi, Ryo*; Hara, Takuhi*; Ohara, Koji*; Kato, Kazuo*; Matsumura, Daiju; Inaba, Yusuke*; Nakase, Masahiko*; Takeshita, Kenji*
Journal of Nuclear Science and Technology, 58(4), p.399 - 404, 2021/04
Times Cited Count:5 Percentile:61.45(Nuclear Science & Technology)Yoneda, Yasuhiro; Kunisada, Ryoichi*; Chikada, Tsukasa*; Ueno, Shintaro*; Fujii, Ichiro*; Nagata, Hajime*; Ohara, Koji*; Wada, Satoshi*
Japanese Journal of Applied Physics, 58(SL), p.SLLA03_1 - SLLA03_7, 2019/11
Times Cited Count:4 Percentile:22.27(Physics, Applied)Li, B.*; Kawakita, Yukinobu; Kawamura, Seiko; Sugahara, Takeshi*; Wang, H.*; Wang, J.*; Chen, Y.*; Kawaguchi, Saori*; Kawaguchi, Shogo*; Ohara, Koji*; et al.
Nature, 567(7749), p.506 - 510, 2019/03
Times Cited Count:182 Percentile:99.31(Multidisciplinary Sciences)Refrigeration is of vital importance for modern society for example, for food storage and air conditioning- and 25 to 30% of the world's electricity is consumed for refrigeration. Current refrigeration technology mostly involves the conventional vapour compression cycle, but the materials used in this technology are of growing environmental concern because of their large global warming potential. As a promising alternative, refrigeration technologies based on solid-state caloric effects have been attracting attention in recent decades. However, their application is restricted by the limited performance of current caloric materials, owing to small isothermal entropy changes and large driving magnetic fields. Here we report colossal barocaloric effects (CBCEs) (barocaloric effects are cooling effects of pressure-induced phase transitions) in a class of disordered solids called plastic crystals. The obtained entropy changes in a representative plastic crystal, neopentylglycol, are about 389 joules per kilogram per kelvin near room temperature. Pressure-dependent neutron scattering measurements reveal that CBCEs in plastic crystals can be attributed to the combination of extensive molecular orientational disorder, giant compressibility and highly anharmonic lattice dynamics of these materials. Our study establishes the microscopic mechanism of CBCEs in plastic crystals and paves the way to next-generation solid-state refrigeration technologies.
Yoneda, Yasuhiro; Ohara, Koji*; Nagata, Hajime*
Japanese Journal of Applied Physics, 57(11S), p.11UB07_1 - 11UB07_6, 2018/11
Times Cited Count:13 Percentile:57.76(Physics, Applied)Local structure analysis of KNbO, which is the parent compound for lead-free piezoelectric materials, have been performed by X-ray pair-distribution functions (PDF). The refinements of local structure in wide temperature ranges indicates that only the rhombohedral structure can describe the observed bond distributions within the unit cell. The rhombohedral distortion maintained locally in all four phases.
Yoneda, Yasuhiro; Kunisada, Ryoichi*; Chikada, Tsukasa*; Ueno, Shintaro*; Ohara, Koji*; Wada, Satoshi*
Transactions of the Materials Research Society of Japan, 43(2), p.93 - 96, 2018/04
KNbO nanocrystals were grown by solvothermal technique assisted by a microwave treatment. We performed high-energy X-ray diffraction to extract average and local structural parameters. The particle size can be evaluated by the Scherrer's equation. The unit cell size was reduced as the particle size increased. The local structure was found to be a rhombohedral structure, which was similar to that of the bulk KNbO.
Li, B.; Wang, H.*; Kawakita, Yukinobu; Zhang, Q.*; Feygenson, M.*; Yu, H. L.*; Wu, D.*; Ohara, Koji*; Kikuchi, Tatsuya*; Shibata, Kaoru; et al.
Nature Materials, 17(3), p.226 - 230, 2018/03
Times Cited Count:110 Percentile:96.86(Chemistry, Physical)Sakaguchi, Yoshifumi; Kira, Hiroshi; Oku, Takayuki; Shinohara, Takenao; Suzuki, Junichi; Sakai, Kenji; Nakamura, Mitsutaka; Suzuya, Kentaro; Aizawa, Kazuya; Arai, Masatoshi; et al.
Journal of Physics; Conference Series, 294(1), p.012004_1 - 012004_7, 2011/06
Times Cited Count:2 Percentile:65.58Sakaguchi, Yoshifumi; Kira, Hiroshi; Oku, Takayuki; Shinohara, Takenao; Suzuki, Junichi; Sakai, Kenji; Nakamura, Mitsutaka; Suzuya, Kentaro; Aizawa, Kazuya; Arai, Masatoshi; et al.
Physica B; Condensed Matter, 406(12), p.2443 - 2447, 2011/06
Sakaguchi, Yoshifumi; Kira, Hiroshi; Oku, Takayuki; Shinohara, Takenao; Suzuki, Junichi; Sakai, Kenji; Nakamura, Mitsutaka; Suzuya, Kentaro; Aizawa, Kazuya; Arai, Masatoshi; et al.
Physica B; Condensed Matter, 406(12), p.2443 - 2447, 2011/06
Times Cited Count:3 Percentile:16.31(Physics, Condensed Matter)Sakaguchi, Yoshifumi; Kira, Hiroshi; Oku, Takayuki; Shinohara, Takenao; Suzuki, Junichi; Sakai, Kenji; Nakamura, Mitsutaka; Suzuya, Kentaro; Arai, Masatoshi; Takeda, Masayasu; et al.
no journal, ,
no abstracts in English
Shimakura, Hironori; Ogata, Norio*; Kawakita, Yukinobu; Ohara, Koji*; Kohara, Shinji*; Takeda, Shinichi*
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Chlorine dioxide has been used as a disinfectant of drinking water because of strong oxidizing activity against various microbial proteins. Chlorine dioxide has a boiling point of 283 K and a melting point of 214 K, and amber liquid at 273 K with density of 1.64. It is known that, in the solid phase, dimerization occurs due to interaction between Cl and O belonging to the neighboring molecule. Focusing onto the inter-molecular correlations of chlorine dioxide in the liquid state, we have measured high energy X-ray diffraction at 204 K and 273 K and performed reverse Monte Carlo (RMC) structure modeling based on the experimental structural data. In order to distinguish the orientational correlation by intermolecular interaction from the geometrical correlation, we compared the results of full RMC results with the structure model of free packing. As a result, its inter-molecular correlation, especially inter-molecular O-O correlation, becomes weak with increasing temperature.
Sakaguchi, Yoshifumi; Kira, Hiroshi; Oku, Takayuki; Shinohara, Takenao; Suzuki, Junichi; Sakai, Kenji; Nakamura, Mitsutaka; Suzuya, Kentaro; Aizawa, Kazuya; Arai, Masatoshi; et al.
no journal, ,
no abstracts in English
Ueno, Hiroki; Kawakita, Yukinobu; Ohara, Koji*; Shimakura, Hironori; Tahara, Shuta*; Kumara, L. S. R.*; Yamaguchi, Hiroshi*; Yasunaga, Akinori*; Wakisaka, Yuiko*; Ito, Masayoshi*; et al.
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Bi-Zn system has a phase diagram with a miscibility gap where critical point is at BiZn. It is known that concentration fluctuation increases on approaching to the miscibility gap. Earlier studies suggested that the miscibility gap is attributed to difference in atomic size between Bi and Zn. Recent developments of instrument and analysis technique enable us to deduce partial structures and demonstrate atomic configurations in liquid. We performed detailed analysis on medium-range structure in liquid BiZn by using neutron diffraction data obtained by the two-axis diffractometer, HERMES, installed in JRR-3M, JAEA and, X-ray diffraction at BL08W beamline in SPring-8, Hyogo, Japan. 3D atomic structural model obtained by Revere Monte Carlo technique exhibits temperature evolution of concentration fluctuations in medium-range structure, which suggests that phase separation tendency appears even in the edge of the miscibility gap of liquid Bi-Zn.
Ueno, Hiroki; Kawakita, Yukinobu; Ohara, Koji*; Tahara, Shuta*; Kohara, Shinji*; Ito, Masayoshi*; Takeda, Shinichi*
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no abstracts in English
Ueno, Hiroki; Kawakita, Yukinobu; Ohara, Koji*; Tahara, Shuta*; Kohara, Shinji*; Ito, Masayoshi*; Takeda, Shinichi*
no journal, ,
Shimakura, Hironori; Kawakita, Yukinobu; Ohara, Koji*; Wakisaka, Yuiko*; Kohara, Shinji*; Takeda, Shinichi*
no journal, ,
no abstracts in English