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213 results on '"Michiue, Yuichi"'

1. A ferroelectric-like structural transition in a metal

Author

Shi, Youguo, Guo, Yanfeng, Wang, Xia, Princep, Andrew J., Khalyavin, Dmitry, Manuel, Pascal, Michiue, Yuichi, Sato, Akira, Tsuda, Kenji, Yu, Shan, Arai, Masao, Shirako, Yuichi, Akaogi, Masaki, Wang, Nanlin, Yamaura, Kazunari, and Boothroyd, Andrew T.

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

Metals cannot exhibit ferroelectricity because static internal electric fields are screened by conduction electrons, but in 1965, Anderson and Blount predicted the possibility of a ferroelectric metal, in which a ferroelectric-like structural transition occurs in the metallic state. Up to now, no clear example of such a material has been identified. Here we report on a centrosymmetric (R-3c) to non-centrosymmetric (R3c) transition in metallic LiOsO3 that is structurally equivalent to the ferroelectric transition of LiNbO3. The transition involves a continuous shift in the mean position of Li+ ions on cooling below 140K. Its discovery realizes the scenario described by Anderson and Blount, and establishes a new class of materials whose properties may differ from those of normal metals., Comment: Manuscript of published version, including Supplementary Information. See also News & Views article by V. Keppens, Nature Materials 12, 952 (2013)

Published
2015
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8. Exfoliated Ferrierite-Related Unilamellar Nanosheets in Solution and Their Use for Preparation of Mixed Zeolite Hierarchical Structures

Author

Roth, Wieslaw J., primary, Sasaki, Takayoshi, additional, Wolski, Karol, additional, Ebina, Yasuo, additional, Tang, Dai-Ming, additional, Michiue, Yuichi, additional, Sakai, Nobuyuki, additional, Ma, Renzhi, additional, Cretu, Ovidiu, additional, Kikkawa, Jun, additional, Kimoto, Koji, additional, Kalahurska, Katarzyna, additional, Gil, Barbara, additional, Mazur, Michal, additional, Zapotoczny, Szczepan, additional, Čejka, Jiri, additional, Grzybek, Justyna, additional, and Kowalczyk, Andrzej, additional

Published
2021
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20. Utilizing a unified structure model in (3 + 1)‐dimensional superspace to identify a homologous phase (Ga1−αAlα)2O3(ZnO)m in ZnO‐based thermoelectric composites.

Author

Michiue, Yuichi, Son, Hyoung-Won, and Mori, Takao

Subjects
*ZINTL compounds, *THERMOELECTRIC materials, *COMPOSITE materials, *X-ray powder diffraction, *ELECTRIC conductivity, *ALUMINUM carbide, *ZINC oxide, *MECHANICAL properties of condensed matter
Abstract

A unified structure model in (3 + 1)‐dimensional superspace proved suitable for identification of a homologous phase (Ga1−αAlα)2O3(ZnO)m by the profile fitting of powder X‐ray diffraction intensities for thermoelectric composite materials in the pseudoternary system ZnO–Al2O3–Ga2O3. A homologous compound of the phase parameter m ≃ 37 was found to coexist with (Al,Ga)‐doped ZnO in samples sintered at 1723 K in air. The thermoelectric properties of the composite materials were closely related to the phase fractions. The higher the phase fraction of (Al,Ga)‐doped ZnO with the wurtzite structure, the higher the electrical conductivity. On the other hand, the homologous compound with the long‐period structure was effective in lowering the thermal conductivity of the materials. [ABSTRACT FROM AUTHOR]

Published
2020
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25. Compositely modulated structures of phosphor materials SrxLi2+xAl2–xO4:Eu2+.

Author

Ooishi, Atsushi, Michiue, Yuichi, Funahashi, Shiro, Takeda, Takashi, and Hirosaki, Naoto

Subjects
*STRONTIUM, *INTERATOMIC distances, *PHOSPHORS, *VALENCE bonds, *CHEMICAL bond lengths, *ION channels
Abstract

Composite crystals SrxLi2+xAl2−xO4:Eu2+ were synthesized and their structures were determined using single‐crystal X‐ray diffraction. The commensurate structure with a modulation wavevector q = 5c*/6 was analyzed in a conventional manner in 3D space, while a structure model in (3+1)‐dimensional superspace was used for the other two crystals with modulation wavevectors slightly differing from 5c*/6. The superstructure of the commensurate phase was described using the space group P4/n and a common superspace group I4/m(00γ)00 was used for the (3+1)D structures of all three crystals. The whole structure of each crystal consists of two substructures. Basis vectors a and b are common, but c is different for the two substructures. The first substructure is a host framework constructed by (Li/Al)O4 tetrahedra sharing edges. A linear connection of cavities is seen to be channel‐like, in which Sr ions locate as guest cations forming the second substructure. The crystal of q = 5c*/6 contains five Sr ions per six cavities in a channel. Sr ions are distributed at seven sites, some of which are partially occupied. Statistical disorder of local structure models for the location of Sr ions in the channel was assumed to explain the results. Such a partially disordered character was also seen in the incommensurate phases and properly embodied by a (3+1)D model containing an atomic domain of the Sr ion with occupational modulation. Plots of the occupation factor, interatomic distances and the bond valence sum at each metal site as functions of t (= x4 − q·r) are roughly identical in the three crystals, which are considered as members of the same series of composite crystals. [ABSTRACT FROM AUTHOR]

Published
2020
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26. Compositely modulated structures of phosphor materials SrxLi2+xAl2–xO4:Eu2+.

Author

Ooishi, Atsushi, Michiue, Yuichi, Funahashi, Shiro, Takeda, Takashi, and Hirosaki, Naoto

Subjects
STRONTIUM, INTERATOMIC distances, PHOSPHORS, VALENCE bonds, CHEMICAL bond lengths, ION channels
Abstract

Composite crystals SrxLi2+xAl2−xO4:Eu2+ were synthesized and their structures were determined using single‐crystal X‐ray diffraction. The commensurate structure with a modulation wavevector q = 5c*/6 was analyzed in a conventional manner in 3D space, while a structure model in (3+1)‐dimensional superspace was used for the other two crystals with modulation wavevectors slightly differing from 5c*/6. The superstructure of the commensurate phase was described using the space group P4/n and a common superspace group I4/m(00γ)00 was used for the (3+1)D structures of all three crystals. The whole structure of each crystal consists of two substructures. Basis vectors a and b are common, but c is different for the two substructures. The first substructure is a host framework constructed by (Li/Al)O4 tetrahedra sharing edges. A linear connection of cavities is seen to be channel‐like, in which Sr ions locate as guest cations forming the second substructure. The crystal of q = 5c*/6 contains five Sr ions per six cavities in a channel. Sr ions are distributed at seven sites, some of which are partially occupied. Statistical disorder of local structure models for the location of Sr ions in the channel was assumed to explain the results. Such a partially disordered character was also seen in the incommensurate phases and properly embodied by a (3+1)D model containing an atomic domain of the Sr ion with occupational modulation. Plots of the occupation factor, interatomic distances and the bond valence sum at each metal site as functions of t (= x4 − q·r) are roughly identical in the three crystals, which are considered as members of the same series of composite crystals. [ABSTRACT FROM AUTHOR]

Published
2020
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29. Reentrant valence transition in YbCu4.5 under pressure

Author

Yamaoka, Hitoshi, primary, Tsujii, Naohito, additional, Yamamoto, Yoshiya, additional, Michiue, Yuichi, additional, Lin, Jung-Fu, additional, Hiraoka, Nozomu, additional, Ishii, Hirofumi, additional, Tsuei, Ku-Ding, additional, and Mizuki, Jun'ichiro, additional

Published
2018
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36. Thermoelectric Properties of Variants of Cu4Mn2Te4with Spinel-Related Structure

Author

Guo, Quansheng, Vaney, Jean-Baptiste, Virtudazo, Raymond, Minami, Ryunosuke, Michiue, Yuichi, Yamabe-Mitarai, Yoko, and Mori, Takao

Abstract

Thermoelectric properties of Cu4Mn2Te4, which is antiferromagnetic with a Néel temperature TN= 50 K and crystallizes in a spinel-related structure, have been investigated comprehensively here. The phase transition occurring at temperatures 463 and 723 K is studied by high-temperature X-ray diffraction (XRD) and differential scanning calorimetry (DSC), and its effect on thermoelectric properties is examined. Hypothetically Cu4Mn2Te4is semiconducting according to the formula (Cu+)4(Mn2+)2(Te2–)4, while experimentally it shows p-type metallic conduction behavior, exhibiting electrical conductivity σ = 2500 Ω–1cm–1and Seebeck coefficient α = 20 μV K–1at 325 K. Herein, we show that the carrier concentration and thus the thermoelectric transport properties could be further optimized through adding electron donors such as excess Mn. Discussions are made on the physical parameters contributing to the low thermal conductivity, including Debye temperature, speed of sound, and the Grüneisen parameter. As a result of simultaneously boosted power factor and reduced thermal conductivity, a moderately high zT= 0.65 at 680 K is obtained in an excess Mn\In co-added sample, amounting to 5 times that of the pristine Cu4Mn2Te4. This value (zT= 0.65) is the best result ever reported for spinel and spinel-related chalcogenides.

Published
2018
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37. A ferroelectric-like structural transition in a metal

Author

Shi, Youguo, primary, Guo, Yanfeng, additional, Wang, Xia, additional, Princep, Andrew J., additional, Khalyavin, Dmitry, additional, Manuel, Pascal, additional, Michiue, Yuichi, additional, Sato, Akira, additional, Tsuda, Kenji, additional, Yu, Shan, additional, Arai, Masao, additional, Shirako, Yuichi, additional, Akaogi, Masaki, additional, Wang, Nanlin, additional, Yamaura, Kazunari, additional, and Boothroyd, Andrew T., additional

Published
2013
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47. Identification of a secondary phase Ga2O3(ZnO)m in Ga‐doped ZnO thermoelectric materials by a (3 + 1)‐dimensional superspace model.

Author

Michiue, Yuichi and Mori, Takao

Subjects
*THERMOELECTRIC effects, *X-ray diffraction, *ZINC oxide, *X-ray powder diffraction, *CRYSTAL structure, *NANOPARTICLES, *THIN films
Abstract

A unified structure model for the homologous compounds Ga2O3(ZnO)m in (3 + 1)‐dimensional superspace was modified by refinements for samples of Ga2O3:ZnO = 1:n (n = 15, 23, 28, 33, 38). The first‐order sine terms in the modulation functions decreased with increasing phase index m. The diffraction intensities of the thermoelectric material Ga2O3:ZnO = 1:98 were best fitted by a two‐phase model containing the wurtzite structure (Ga‐doped ZnO) and the homologous compound Ga2O3(ZnO)s, where s = 38. [ABSTRACT FROM AUTHOR]

Published
2018
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