研究者詳細 - 中埜　彰俊

論文 - 中埜　彰俊

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放射光X線回折によるRuddlesden-Popper型酸化物Li2SrNb2O7の結晶構造解析

中埜彰俊, 永井隆之, 澤博, 寺崎一郎, 谷口博基

日本物理学会講演概要集 74.1 巻 ( 0 ) 頁： 2550 - 2550 2019年

Ruddlesden-Popper型酸化物Li2SrNb2O7における誘電特性

永井隆之, 中埜彰俊, 森分博紀, 澤博, 寺崎一郎, 谷口博基

日本物理学会講演概要集 74.1 巻 ( 0 ) 頁： 2549 - 2549 2019年

アルミネートソーダライト型酸化物(Ca1-xSrx)8[AlO2]12(MoO4)2 (0.5≦x≦1.0) のリエントラント構造相転移

青木伸雅, 中埜彰俊, 中平夕貴, 森吉千佳子, 黒岩芳弘, 寺崎一郎, 谷口博基

日本物理学会講演概要集 74.1 巻 ( 0 ) 頁： 2551 - 2551 2019年

Antiferroelectric distortion with anomalous phonon softening in the excitonic insulator Ta2NiSe5 査読有り

98 巻 ( 4 ) 2018年7月

Pressure-induced coherent sliding-layer transition in the excitonic insulator Ta2NiSe5

5 巻 ( Pt 2 ) 頁： 158-165 2018年3月

Theoretical and data-driven approaches to semiconductors and dielectrics: from prediction to experiment 査読有り Open Access

Oba, F; Nagai, T; Katsube, R; Mochizuki, Y; Tsuji, M; Deffrennes, G; Hanzawa, K; Nakano, A; Takahashi, A; Terayama, K; Tamura, R; Hiramatsu, H; Nose, Y; Taniguchi, H

SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 25 巻 ( 1 ) 頁： 2423600 2024年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Science and Technology of Advanced Materials

Computational approaches using theoretical calculations and data scientific methods have become increasingly important in materials science and technology, with the development of relevant methodologies and algorithms, the availability of large materials data, and the enhancement of computer performance. As reviewed herein, we have developed computational methods for the design and prediction of inorganic materials with a particular focus on the exploration of semiconductors and dielectrics. High-throughput first-principles calculations are used to systematically and accurately predict the local atomic and electronic structures of polarons, point defects, surfaces, and interfaces, as well as bulk fundamental properties. Machine learning techniques are utilized to efficiently predict various material properties, construct phase diagrams, and search for materials satisfying target properties. These computational approaches have elucidated the mechanisms behind material functionalities and explored promising materials in combination with synthesis, characterization, and device fabrication. Examples include the development of ternary nitride semiconductors for potential optoelectronic and photovoltaic applications, the exploration of phosphide semiconductors and the optimization of heterointerfaces toward the improvement of phosphide-based photovoltaic cells, and the discovery of ferroelectricity in layered perovskite oxides and the theoretical understanding of its origin, all of which demonstrate the effectiveness of our computer-aided materials research.

DOI： 10.1080/14686996.2024.2423600

Unconventional Polarization Response in Titanite-Type Oxides due to Hashed Antiferroelectric Domains 査読有り国際誌

Taniguchi, H; Watanabe, T; Kuwano, T; Nakano, A; Sato, Y; Hagiwara, M; Yokota, H; Deguchi, K

ACS NANO 18 巻 ( 22 ) 頁： 14523 - 14531 2024年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Nano

Domains in a crystal, which have crystallographic uniformity and are geometrically segmented, typically arise from various phase transitions. The physical properties within individual domains are inherently the same as those in the homogeneous bulk. As a result, sufficiently large domains have little influence on the bulk properties. However, as the domains decrease in size to the nanoscale, for instance, due to multiple phase instabilities or spatial inhomogeneities, then the materials often acquire exceptional functionalities that are unattainable without these domains. This effect is exemplified by the ultrahigh dielectric and piezoelectric responses observed in ferroelectric oxides with nanoscale polar domains as well as in ferroelectric relaxors with polar nanoclusters. Here, we demonstrate that hashed nanoscale domains in an antiferroelectric material are also capable of boosting dielectric permittivity in an unconventional way. This discovery has been made in an antiferroelectric titanite-type oxide, CaTi(Si1-xGex)O5, in which the permittivity significantly increases when the antiferroelectric order becomes short-range. Our transmission electron microscopy observations have clarified that polar regions simultaneously appear around antiphase boundaries in the antiferroelectric phase of CaTi(Si1-xGex)O5. As the concentration of the antiphase boundary increases, the polar regions become denser and play a crucial role in boosting the permittivity. At the composition of x = 0.5, the value of the permittivity finally reaches double that in the bulk and shows excellent linearity, at least until an electric field of 500 kV/cm is applied. The present findings highlight the promise of domain engineering for boosting the permittivity in antiferroelectrics as a way to develop materials with excellent dielectric properties.

DOI： 10.1021/acsnano.4c02168

Web of Science

Scopus

PubMed

Molecular orbital formation and metastable short-range ordered structure in VO2 査読有り国際誌

Kitou, S; Nakano, A; Imaizumi, M; Nakamura, Y; Terasaki, I; Arima, TH

PHYSICAL REVIEW B 109 巻 ( 10 ) 2024年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B

The metal-insulator transition (MIT) in vanadium dioxide (VO2) due to V-V dimerization has been extensively discussed for decades. While it is widely acknowledged that electron correlations, Peierls instabilities, and molecular orbital formations are crucial for understanding the MIT of VO2, the primary origin of the MIT remains controversial. In this study, we delve into the crystal structure and orbital state of VO2 through synchrotron x-ray diffraction experiments. The molecular orbital formation corresponding to the V-V dimerization is directly observed in the low-temperature insulating monoclinic phase, called the M1 phase, as indicated by the valence electron density distribution. Moreover, diffuse scattering observed in the high-temperature metal phase of rutile structure suggests the presence of short-range correlation of V displacements, which is not directly attributed to the structural fluctuation of the M1 phase. The short-range order in the rutile phase will be the key to understanding the MIT in this system.

DOI： 10.1103/PhysRevB.109.L100101

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Scopus

その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.109.L100101/fulltext

Fabrication and Thermoelectric Properties of Freestanding Ba1/3CoO2 Single-Crystalline Films

Kang, K; Kato, F; Nakano, A; Terasaki, I; Endo, T; Matsuo, Y; Jeen, H; Ohta, H

ACS APPLIED ELECTRONIC MATERIALS 5 巻 ( 10 ) 頁： 5749 - 5754 2023年10月

掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Electronic Materials

Thermoelectric energy conversion has attracted attention as an energy-harvesting technology for converting waste heat into electricity via the Seebeck effect. Conducting oxide-based thermoelectric materials that exhibit a high figure of merit are promising because of their good chemical and thermal stability as well as their harmless nature compared to chalcogenide-based state-of-the-art thermoelectric materials. Among many conducting oxides, Ba1/3CoO2 epitaxial films exhibit the highest figures of merit. For the practical use of Ba1/3CoO2, bulk ceramics or single-crystalline Ba1/3CoO2 is necessary. Here, we show that freestanding Ba1/3CoO2 single-crystalline films can be fabricated by peeling Ba1/3CoO2 epitaxial films from the substrate. We fabricated Ba1/3CoO2 epitaxial films and immersed them in 40 °C hot water for several tens of minutes. Subsequently, the Ba1/3CoO2 epitaxial film spontaneously peeled off and floated on the surface of the water like seaweed. We measured and analyzed the crystal structure, chemical composition, and thermoelectric properties before and after peeling and realized that there was no significant difference. The present results provide a useful method for fabricating freestanding single-crystalline oxide films for thermoelectrics.

DOI： 10.1021/acsaelm.3c01129

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Scopus

Phase variation of ferroelectric Li2Sr1-xCax(Nb1-xTax)2O7 by selective reinforcement in the (Nb,Ta)-O covalent bonds

Nakano, A; Shirakuni, H; Nagai, T; Mochizuki, Y; Oba, F; Yokota, H; Kawaguchi, S; Terasaki, I; Taniguchi, H

PHYSICAL REVIEW MATERIALS 6 巻 ( 4 ) 2022年4月

掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review Materials

A phase variation of a pseudo-Roddlesden-Popper-type ferroelectric oxide Li2Sr1-xCax(Nb1-xTax)2O7 is systematically investigated using dielectric measurements, second harmonic generation, and x-ray diffraction experiments. We find an exotic x-T phase diagram, including paraelectric Cmcm, antiferroelectric Pmcn, and in-plane antiferroelectric and out-of-plane ferroelectric P21cn phases. At low x, we observe large and divergent dielectric anomalies associated with phase transitions from Cmcm to P21cn, whereas these become small kinks at high x. Structural analyses reveal an internal distortion, and the rotation of octahedra strongly depends on x, which is consistent with the lattice dynamics obtained by a density functional theory calculation. These results demonstrate the great tunability of dielectric properties in layered perovskite-type oxides by tuning the chemical bonding state in the octahedron.

DOI： 10.1103/PhysRevMaterials.6.044412

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Scopus

Hybridization-Gap Formation and Superconductivity in the Pressure-Induced Semimetallic Phase of the Excitonic Insulator Ta2NiSe5

Matsubayashi, K; Okamura, H; Mizokawa, T; Katayama, N; Nakano, A; Sawa, H; Kaneko, T; Toriyama, T; Konishi, T; Ohta, Y; Arima, H; Yamanaka, R; Hisada, A; Okada, T; Ikemoto, Y; Moriwaki, T; Munakata, K; Nakao, A; Nohara, M; Lu, YF; Takagi, H; Uwatoko, Y

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 90 巻 ( 7 ) 頁： 074706 - 074706 2021年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

The excitonic insulator Ta2NiSe5 experiences a first-order structural transition under pressure from rippled to flat layer-structure at Ps ~ 3 GPa, which drives the system from an almost zero-gap semiconductor to a semimetal. The pressure-induced semimetal, with lowering temperature, experiences a transition to another semimetal with a partial-gap of ~0.1-0.2 eV, accompanied with a monoclinic distortion analogous to that occurs at the excitonic transition below Ps. We argue that the partial-gap originates primarily from a symmetry-allowed hybridization of Ta-conduction and Nivalence bands due to the lattice distortion, indicative of the importance of electron-lattice coupling. The transition is suppressed with increasing pressure to Pc ~ 8 GPa. Superconductivity with a maximum Tsc ~ 1.2K emerges around Pc, likely mediated by strongly electron-coupled soft phonons. The electron-lattice coupling is as important ingredient as the excitonic instability in Ta2NiSe5.

DOI： 10.7566/JPSJ.90.074706

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Scopus

Thermal Diffusivity of the Mott Insulator Ca2RuO4 in a Non-equilibrium Steady State 査読有り

Kawasaki, S; Nakano, A; Taniguchi, H; Cho, HJ; Ohta, H; Nakamura, F; Terasaki, I

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 90 巻 ( 6 ) 頁： 063601 - 063601 2021年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

We have measured and analyzed the in-plane thermal diffusivity of the Mott insulator Ca2RuO4 around room temperature under external currents with an infrared camera as a contactless thermometer. We find that the thermal diffusivity decreases by 40% for an external current density of 14 A=cm2. This large impact on lattice properties highly nontrivial in the sense that the external current primarily affects the electronic states. A possible explanation for this is discussed.

DOI： 10.7566/JPSJ.90.063601

Web of Science

Scopus

Ga-substitution effects on the improper ferroelectric phase transition of Ca8[AlO2]12(MoO4)2 査読有り

Maruyama, K; Nakano, A; Terasaki, I; Taniguchi, H

OPEN CERAMICS 5 巻 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Open Ceramics

The aluminum-sodalite-type oxide, Ca8[AlO2]12(MoO4)2, shows an improper ferroelectricity below a ferroelectric phase transition temperature around 630 K. Here we present effects of a Ga-substitution for Al on ferroelectric properties of Ca8[AlO2]12(MoO4)2. Systematic investigations with synchrotron x-ray powder diffractions and dielectric/pyroelectric measurements have clarified that the Ga-substitution suppresses the ferroelectricity and markedly enhances a thermal hysteresis of the ferroelectric phase transition. In contrast to the case of Sr-substitution for Ca, with which the ground state results in a relaxor-like state, the polar ordering of macroscopic scale has been found to survive under the Ga-substitution. The present results shed light on intuitive designing of ferroelectricity and the phase transition properties in the aluminum-sodalite-type oxide.

DOI： 10.1016/j.oceram.2021.100080

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Scopus

Coexisting Mechanisms for the Ferroelectric Phase Transition in Li2SrNb2O7 査読有り

Mochizuki Yasuhide, Nagai Takayuki, Shirakuni Hirokazu, Nakano Akitoshi, Oba Fumiyasu, Terasaki Ichiro, Taniguchi Hiroki

CHEMISTRY OF MATERIALS 33 巻 ( 4 ) 頁： 1257 - 1264 2021年2月

Permittivity boosting in "yellow" (Nb plus In) co-doped TiO2 査読有り

Taniguchi Hiroki, Sato Daiki, Nakano Akitoshi, Terasaki Ichiro

JOURNAL OF MATERIALS CHEMISTRY C 8 巻 ( 39 ) 頁： 13627 - 13631 2020年10月

Non-equilibrium Steady State in the Mott Insulator Ca2RuO4 査読有り

Terasaki Ichiro, Sano Isuzu, Toda Kosuke, Kawasaki Shuji, Nakano Akitoshi, Taniguchi Hiroki, Cho Hai Jun, Ohta Hiromichi, Nakamura Fumihiko

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 89 巻 ( 9 ) 2020年9月

Intercalated Cu+ ion dynamics in the two-dimensional layered compound Cu0.33TiSe2 査読有り

Kitou Shunsuke, Hasegawa Takumi, Nakano Akitoshi, Katayama Naoyuki, Tsutsui Satoshi, Sawa Hiroshi

PHYSICAL REVIEW B 101 巻 ( 9 ) 2020年3月

Phase Transition from Weak Ferroelectricity to Incipient Ferroelectricity in Li2Sr(Nb1-xTax)2O-7 査読有り

Nagai Takayuki, Mochizuki Yasuhide, Shirakuni Hirokazu, Nakano Akitoshi, Oba Fumiyasu, Terasaki Ichiro, Taniguchi Hiroki

CHEMISTRY OF MATERIALS 32 巻 ( 2 ) 頁： 744 - 750 2020年1月

低エネルギー逆光電子分光によるTa2NiSe5の伝導帯の直接観測

川村啓太, 寺崎一郎, 吉田弘幸, 佐藤晴輝, 折尾響, 杉本高大, 太田幸則, 大槻太毅, 吉田鉄平, 丸岡うらら, 中埜彰俊

日本表面真空学会学術講演会要旨集 2020 巻 ( 0 ) 2020年

出版者・発行元：公益社団法人日本表面真空学会

Ta2NiSe5は励起子絶縁体の候補である。既に価電子帯端の低温での低エネルギーシフトが報告されており、伝導帯の観測が切望されている。本研究では低エネルギー逆光電子分光法で伝導帯を直接観測した。フェルミ準位から0.55 eVに観測されたバンドは80 Kでもエネルギーが変化しなかった。これは、従来の励起子絶縁体とは異なり、バンドギャップが強い電子正孔相互作用により開いた状態であるという描像と整合する。

DOI： 10.14886/jvss.2020.0_135

Weak Ferroelectricity in n=2 Pseudo Ruddlesden-Popper-Type Niobate Li2SrNb2O7 査読有り

Nagai Takayuki, Shirakuni Hirokazu, Nakano Akitoshi, Sawa Hiroshi, Moriwake Hiroki, Terasaki Ichiro, Taniguchi Hiroki

CHEMISTRY OF MATERIALS 31 巻 ( 16 ) 頁： 6257 - 6261 2019年8月

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