研究者詳細 - 三浦　飛鳥

論文 - 三浦　飛鳥

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Improving thermoelectric properties of Bi<inf>2</inf>Te<inf>3</inf> by straining under high pressure: Experiment and DFT calculation 査読有り国際誌

Wang Q., Tang Y., Miura A., Miyazaki K., Horita Z., Iikubo S.

Scripta Materialia 243 2024年04月

記述言語：英語掲載種別：研究論文（学術雑誌）

Bi2Te3 intermetallic compounds show high thermoelectric performance near room temperature and are widely used for cooling and power generation applications. It is still necessary to improve its dimensionless figure of merit zT for large-scale industrial use. In this study, high-pressure torsion processing is applied to Bi2Te3 powder samples to investigate the crystal structure and enhance their thermoelectric properties. The processed Bi2Te3 samples show reduced cell volume, higher electrical conductivity, enhanced Seebeck coefficient and higher zT value compared with the original powder sample, even if the grain refinement is not remarkable. First-principles calculations are also used to investigate the electronic structure and thermoelectric properties to clarify the influence of high-pressure torsion processing.

DOI： 10.1016/j.scriptamat.2024.115991

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THERMAL CONDUCTIVITY OF A PRINTED THERMOELECTRIC FILM 査読有り国際誌

Kosuke Watanabe, Asuka Miura, Tomohide Yabuki, Koji Miyazaki

17th International Heat Transfer Conference ( IHTC ) 2023年08月

Thermoelectric Properties of Halide Perovskite Thin Films 査読有り国際誌

Kosuke Watanabe, Asuka Miura, Tomohide Yabuki, Koji Miyazaki

30th International Workshop on Active-Matrix Flatpanel Displays and Devices: TFT Technologies and FPD Materials 2023年07月

Direct Electrical Probing of Anomalous Nernst Conductivity 査読有り国際誌

Zhou W., Miura A., Sakuraba Y., Uchida K.

Physical Review Applied 19 ( 6 ) 2023年06月

記述言語：英語掲載種別：研究論文（学術雑誌）

Despite the usefulness of the anomalous Nernst conductivity (αxyA) for studying electronic band structures and exploring magnetic materials with large transverse thermopower, there has not been a straightforward way to obtain αxyA in experiments. Here we propose a simple and versatile method enabling direct electrical probing of αxyA, which is realized by creating a closed circuit consisting of a target magnetic material and a nonmagnetic conductor. This method is experimentally demonstrated on a thin film of the magnetic Weyl semimetal Co2MnGa, where the closed circuit is formed simply by our connecting both ends of the Co2MnGa film with a Au wire. A good approximation of αxyA is obtained in a wide temperature range, validating the proposed method and showing its potential for aiding the further development of topological-materials science and transverse thermoelectrics.

DOI： 10.1103/PhysRevApplied.19.064079

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Seebeck-driven transverse thermoelectric generation in magnetic hybrid bulk materials 査読有り国際誌

Weinan Zhou, Asuka Miura, Takamasa Hirai, Yuya Sakuraba, and Ken-ichi Uchida

Applied Physics Letters ( AIP Publishing ) 122 062402 2023年02月

Thermoelectric Properties of Halide Perovskite Thin Films 査読有り

Watanabe K., Miura A., Yabuki T., Miyazaki K.

30th International Workshop on Active-Matrix Flatpanel Displays and Devices: TFT Technologies and FPD Materials, AM-FPD 2023 - Proceedings 75 - 77 2023年01月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

One-step solution processed Cesium Tin halide perovskites (CsSnI3) known as lead-free halide perovskite were explored for thermoelectric applications. We report thermoelectric properties of CsSnI3 with some dopants, such as In, Sb, Ni, Mg and Cu in different concentrations (50, 100 ppm) to control the carrier concentration. The fabricated thin film shows p-Type characteristics and their power factors were around 100μW/(m2· K) with any dopants in different concentrations. Their properties agreed with ab-initio calculation for CsSnI3 under the constant relaxation time assumption (τ=2×10-14 s). The high electrical conductivity is realized by Sn4+ increase (Sn2+ oxidation) was confirmed by XPS measurements. Thermal conductivity was also measured to be around 0.3 W/(m· K) by differential 3ω method. The printable materials will will help for further development of direct thermal energy harvesting devices near room temperature.

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THERMAL CONDUCTIVITY OF A PRINTED THERMOELECTRIC FILM 査読有り

Watanabe K., Miura A., Yabuki T., Miyazaki K.

International Heat Transfer Conference 2023年01月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

We made composite films of Bismuth Telluride and Halide Perovskite at different sintering temperatures and characterized their thermoelectric properties. We aimed to improve thermoelectric properties through the reduction of effective thermal conductivity by using the interfacial thermal resistance between Halide Perovskite and Bismuth Telluride particles. Halide perovskite has been well investigated for a solar cell as one of the printable semiconductor materials. Here, we utilized Halide Perovskite as a thermoelectric material. The samples were prepared by printing and sintering the ink consisting of Bismuth Telluride powder produced by mechanical grinding and a precursor solution of Halide Perovskite. The thermoelectric performance was evaluated by a dimensionless figure-of-merit ZT at room temperature. The power factor of the composite films was higher than that of the pure Bismuth Telluride printed film, and the maximum value of power factor 205 μW/(m·K2) was obtained annealed at 350 °C. The thermal conductivity of the film was measured by bi-directional 3ω method. Compared the measured thermal conductivity of the composite film with the calculated thermal conductivity by simple models, we found that the thermal conductivity was greatly reduced by the high interfacial thermal resistance between Bismuth Telluride and Halide Perovskite. The proposed composite technique will be a promising method for improving both the thermoelectric properties and production cost performance.

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Elastocaloric Kirigami Temperature Modulator 査読有り国際誌

Hirai T., Iguchi R., Miura A., Uchida K.i.

Advanced Functional Materials 32 ( 28 ) 2022年07月

記述言語：英語掲載種別：研究論文（学術雑誌）

The elastocaloric effect, a temperature change induced by the external tensile or compressive strain, is of crucial interest for next-generation thermal management technologies because of its environmental friendliness and economic benefits. Toward applications of the elastocaloric effect, many efforts have been made to determine highly efficient elastocaloric materials. Here, another way of modulating the elastocaloric temperature change is reported by applying a process inspired by the Japanese art of paper-cutting, named kirigami. Simply, by stretching elastocaloric materials with kirigami structure, it is demonstrated that focused heat absorption and release can be generated simultaneously owing to nonuniform internal stress by cutting patterns. Owing to the ultrahigh stretchability of kirigami, the input stress required to generate the elastocaloric temperature change is dramatically reduced, resulting in an improvement in the local cooling/heating performance. The concept demonstrated here can be applied to any elastocaloric material and pave the way for constructing versatile solid-state heat pumps for flexible electronics.

DOI： 10.1002/adfm.202201116

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Phase-transition-induced giant Thomson effect for thermoelectric cooling 査読有り国際誌

Modak R., Murata M., Hou D., Miura A., Iguchi R., Xu B., Guo R., Shiomi J., Sakuraba Y., Uchida K.I.

Applied Physics Reviews 9 ( 1 ) 2022年03月

記述言語：英語掲載種別：研究論文（学術雑誌）

The Seebeck and Peltier effects have been widely studied and used in various thermoelectric technologies, including thermal energy harvesting and solid-state heat pumps. However, basic and applied studies on the Thomson effect, another fundamental thermoelectric effect in conductors, are limited despite the fact that the Thomson effect allows electronic cooling through the application of a temperature gradient bias rather than the construction of junction structures. In this article, we report the observation of a giant Thomson effect that appears owing to magnetic phase transitions. The Thomson coefficient of FeRh-based alloys reaches large values approaching -1000 μV K-1 around room temperature because of the steep temperature dependence of the Seebeck coefficient associated with the antiferromagnetic-ferromagnetic phase transition. The Thomson coefficient is several orders of magnitude larger than the Seebeck coefficient of the alloys. Using the active thermography technique, we demonstrate that the Thomson cooling can be much larger than Joule heating in the same material even in a nearly steady state. The operation temperature of the giant Thomson effect in the FeRh-based alloys can be tuned over a wide range by applying an external magnetic field or by slightly changing the composition. Our findings provide a new direction in the materials science of thermoelectrics and pave the way for thermal management applications using the Thomson effect.

DOI： 10.1063/5.0077497

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Process gas dependence of the spin Peltier effect in Pt/Fe<inf>3</inf>O<inf>4</inf>hybrid structures 査読有り国際誌

Itoh T., Miura A., Uchida K.I., Yanagihara H.

Applied Physics Express 15 ( 1 ) 2022年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

The spin Peltier effect (SPE) in Pt/Fe3O4 hybrid structures with epitaxial Fe3O4 layers synthesized by reactive sputtering using two different process gases, Ar/O2 and Kr/O2, was investigated. The magnitude of the SPE-induced temperature modulation for the Fe3O4 film grown using Kr/O2 was approximately 40% larger than that grown using Ar/O2 despite almost the same crystalline structures and magnetic and electric properties of the films. The enhancement of the SPE signal for the film grown with Kr/O2 can be attributed to an increase in the spin current injected into the Fe3O4 film owing to its large roughness.

DOI： 10.35848/1882-0786/ac44c9

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冷感マスクの赤外域放射特性査読有り

長野利春, 早川翔大, 三浦飛鳥, 渡邊厚介, 矢吹智英, 宮崎康次

熱物性 ( 日本熱物性学会 ) 36 ( 4 ) 132 - 136 2022年01月

記述言語：日本語掲載種別：研究論文（学術雑誌）

<p>冷感マスクの冷却効果をふく射伝熱によって考察するため，それらの垂直入射-半球反射スペクトルを測定した．ポリエステル，ナイロン，綿，ポリプロピレンを主成分とする5種類のマスク，比較のため2種のインナー，1種の日傘で合計8種を測定対象とした．ポリエステルを主成分とする素材が放射伝熱冷却に優れている測定結果が得られ，3μm以下の可視光域で反射率が高く，赤外域で低かった．測定結果に基づき放射冷却に着目した性能指数を導入し，冷却マスクの放射冷却メカニズムを考察した．走査電子顕微鏡で観察し，表面に光学干渉する特徴的構造がなく，材料の持つ光学特性がふく射伝熱冷却性能を決めていると考えられる．</p>

DOI： 10.2963/jjtp.36.132

Magneto-optical design of anomalous Nernst thermopile 査読有り国際誌

Wang J., Miura A., Modak R., Takahashi Y.K., Uchida K.i.

Scientific Reports 11 ( 1 ) 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

The introduction of spin caloritronics into thermoelectric conversion has paved a new path for versatile energy harvesting and heat sensing technologies. In particular, thermoelectric generation based on the anomalous Nernst effect (ANE) is an appealing approach as it shows considerable potential to realize efficient, large-area, and flexible use of heat energy. To make ANE applications viable, not only the improvement of thermoelectric performance but also the simplification of device structures is essential. Here, we demonstrate the construction of an anomalous Nernst thermopile with a substantially enhanced thermoelectric output and simple structure comprising a single ferromagnetic material. These improvements are achieved by combining the ANE with the magneto-optical recording technique called all-optical helicity-dependent switching of magnetization. Our thermopile consists only of Co/Pt multilayer wires arranged in a zigzag configuration, which simplifies microfabrication processes. When the out-of-plane magnetization of the neighboring wires is reversed alternately by local illumination with circularly polarized light, the ANE-induced voltage in the thermopile shows an order of magnitude enhancement, confirming the concept of a magneto-optically designed anomalous Nernst thermopile. The sign of the enhanced ANE-induced voltage can be controlled reversibly by changing the light polarization. The engineering concept demonstrated here promotes effective utilization of the characteristics of the ANE and will contribute to realizing its thermoelectric applications.

DOI： 10.1038/s41598-021-90865-5

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Erratum: Phenomenological analysis of transverse thermoelectric generation and cooling performance in magnetic/thermoelectric hybrid systems (J. Appl. Phys. (2021) 129 (223908) DOI: 10.1063/5.0055475) 査読有り国際誌

Yamamoto K., Iguchi R., Miura A., Zhou W., Sakuraba Y., Miura Y., Uchida K.I.

Journal of Applied Physics 130 ( 3 ) 2021年07月

記述言語：英語掲載種別：記事・総説・解説・論説等（その他）

line of text are correct below. (Formula presented) where we assumed ZtotT≪1 and the liner temperature gradient. All online versions of the article were corrected on 18 June 2021. AIP Publishing apologizes for this error..

DOI： 10.1063/5.0061893

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Temperature dependence of anisotropic magneto-Seebeck effect in NiPt alloys 査読有り国際誌

Hirai T., Modak R., Miura A., Seki T., Takanashi K., Uchida K.I.

Applied Physics Express 14 ( 7 ) 2021年07月

記述言語：英語掲載種別：研究論文（学術雑誌）

This letter reports systematic measurements of the anisotropic magneto-Seebeck effect (AMSE) of ferromagnetic Ni100-x Pt x alloys with different Pt concentration ratios x. By simultaneously measuring an applied temperature difference and generated thermopower at the same positions, the Seebeck coefficient under a magnetic field is quantified with high reliability at the temperatures ranging from 300 to 550 K. The AMSE of the alloys is maximized at around x = 5 at% in the high temperature range and disappears at the temperatures lower than the Curie temperature. The systematic dataset and experimental techniques established here will invigorate spin caloritronics studies.

DOI： 10.35848/1882-0786/ac057c

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Phenomenological analysis of transverse thermoelectric generation and cooling performance in magnetic/thermoelectric hybrid systems 査読有り国際誌

Yamamoto K., Iguchi R., Miura A., Zhou W., Sakuraba Y., Miura Y., Uchida K.I.

Journal of Applied Physics 129 ( 22 ) 2021年06月

記述言語：英語掲載種別：研究論文（学術雑誌）

We phenomenologically calculate the performance of the recently observed Seebeck-driven transverse thermoelectric generation (STTG) for various systems in terms of the thermopower, power factor, and figure of merit to demonstrate the usefulness of STTG. The STTG system consists of a closed circuit comprising thermoelectric and magnetic materials which exhibit the Seebeck and anomalous Hall effects, respectively. When a temperature gradient is applied to the hybrid system, the Seebeck effect in the thermoelectric material layer generates a longitudinal charge current in the closed circuit, and the charge current subsequently drives the anomalous Hall effect in the magnetic material layer. The anomalous Hall voltage driven by the Seebeck effect has a similar symmetry to the transverse thermoelectric conversion based on the anomalous Nernst effect. We find that the thermoelectric properties of STTG can be much better than those of the anomalous Nernst effect by increasing the Seebeck coefficient and anomalous Hall angle of the thermoelectric and magnetic materials, respectively, as well as by optimizing their dimensions. We also formulate the electronic cooling performance in the STTG system, thereby confirming the reciprocal relation for the hybrid transverse thermoelectric conversion.

DOI： 10.1063/5.0055475

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Thermal properties of single-walled carbon nanotube forests with various volume fractions 査読有り国際誌

Cha J.H., Hasegawa K., Lee J., Stein I.Y., Miura A., Noda S., Shiomi J., Chiashi S., Wardle B.L., Maruyama S.

International Journal of Heat and Mass Transfer 171 2021年06月

記述言語：英語掲載種別：研究論文（学術雑誌）

Needs of a material for thermal management in reduced-sized electronic devices drive single-walled carbon nanotubes (SWCNTs) to be one of the most promising candidates due to their excellent thermal properties. Many numerical and experimental studies have reported on understanding thermal properties of the SWCNT for thermal device applications. In the present study, thermal diffusivity and conductivity of SWCNT forests in the axial direction with various volume fractions of SWCNTs were measured by laser flash analysis technique and the same properties of an individual SWCNT were derived. The volume fraction was controlled up to 25 vol% by biaxial mechanical densification which maintains SWCNT alignment. While the thermal diffusivity of SWCNT forests was almost constant, it increased when the volume fraction was higher than 17 vol%, suggesting that some SWCNTs, which did not serve as a thermal path in the case of lower volume fraction, were connected with the other SWCNTs. Through the increase of inferred thermal conductivity equivalent to an individual SWCNT after 17 vol%, we also realized that the enhancement of volume fraction of SWCNT forest diminished thermal boundary resistance in good agreement with the tendency inferred from the reported numerical data.

DOI： 10.1016/j.ijheatmasstransfer.2021.121076

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Seebeck-driven transverse thermoelectric generation 査読有り国際誌

Zhou W., Yamamoto K., Miura A., Iguchi R., Miura Y., Uchida K.i., Sakuraba Y.

Nature Materials 20 ( 4 ) 463 - 467 2021年04月

記述言語：英語掲載種別：研究論文（学術雑誌）

When a temperature gradient is applied to a closed circuit comprising two different conductors, a charge current is generated via the Seebeck effect1. Here, we utilize the Seebeck-effect-induced charge current to drive ‘transverse’ thermoelectric generation, which has great potential for energy harvesting and heat sensing applications owing to the orthogonal geometry of the heat-to-charge-current conversion2–9. We found that, in a closed circuit comprising thermoelectric and magnetic materials, artificial hybridization of the Seebeck effect into the anomalous Hall effect10 enables transverse thermoelectric generation with a similar symmetry to the anomalous Nernst effect11–27. Surprisingly, the Seebeck-effect-driven transverse thermopower can be several orders of magnitude larger than the anomalous-Nernst-effect-driven thermopower, which is clearly demonstrated by our experiments using Co2MnGa/Si hybrid materials. The unconventional approach could be a breakthrough in developing applications of transverse thermoelectric generation.

DOI： 10.1038/s41563-020-00884-2

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Above-room-temperature giant thermal conductivity switching in spintronic multilayers 査読有り国際誌

Nakayama H., Xu B., Iwamoto S., Yamamoto K., Iguchi R., Miura A., Hirai T., Miura Y., Sakuraba Y., Shiomi J., Uchida K.I.

Applied Physics Letters 118 ( 4 ) 2021年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

Thermal switching provides an effective way for active heat flow control, which has recently attracted increasing attention in terms of nanoscale thermal management technologies. In magnetic and spintronic materials, the thermal conductivity depends on the magnetization configuration: this is the magnetothermal resistance effect. Here, we show that an epitaxial Cu/Co50Fe50 multilayer film exhibits giant magnetic-field-induced modulation of the cross-plane thermal conductivity. The magnetothermal resistance ratio for the Cu/Co50Fe50 multilayer reaches 150% at room temperature, which is much larger than the previous record high. Although the ratio decreases with increasing the temperature, the giant magnetothermal resistance effect of ∼100% still appears up to 400 K. The magnetic field dependence of the thermal conductivity of the Cu/Co50Fe50 multilayer was observed to be about twice greater than that of the cross-plane electrical conductivity. The observation of the giant magnetothermal resistance effect clarifies the potential of spintronic multilayers as thermal switching devices.

DOI： 10.1063/5.0032531

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Enhancement of the anomalous Nernst effect in Ni/Pt superlattices 査読有り国際誌

Seki T., Sakuraba Y., Masuda K., Miura A., Tsujikawa M., Uchida K., Kubota T., Miura Y., Shirai M., Takanashi K.

Physical Review B 103 ( 2 ) 2021年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

We report an enhancement of the anomalous Nernst effect (ANE) in Ni/Pt (001) epitaxial superlattices. The transport and magnetothermoelectric properties were investigated for the Ni/Pt superlattices with various Ni layer thicknesses (t). The anomalous Nernst coefficient was increased up to more than 1μVK-1 for 2.0nm≤t≤4.0nm, which was the remarkable enhancement compared to the bulk Ni. It has been found that the large transverse thermoelectric conductivity (αxy), reaching αxy=4.8AK-1m-1 for t=4.0nm, plays a prime role for the enhanced ANE of the Ni/Pt (001) superlattices.

DOI： 10.1103/PhysRevB.103.L020402

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Simultaneous harvesting of radiative cooling and solar heating for transverse thermoelectric generation 査読有り国際誌

Ishii S., Miura A., Nagao T., Uchida K.i.

Science and Technology of Advanced Materials 22 ( 1 ) 441 - 448 2021年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

For any thermoelectric effects to be achieved, a thermoelectric material must have hot and cold sides. Typically, the hot side can be easily obtained by excess heat. However, the passive cooling method is often limited to convective heat transfer to the surroundings. Since thermoelectric voltage is proportional to the temperature difference between the hot and cold sides, efficient passive cooling to increase the temperature gradient is of critical importance. Here, we report simultaneous harvesting of radiative cooling at the top and solar heating at the bottom to enhance the temperature gradient for a transverse thermoelectric effect which generates thermoelectric voltage perpendicular to the temperature gradient. We demonstrate this concept by using the spin Seebeck effect and confirm that the spin Seebeck device shows the highest thermoelectric voltage when both radiative cooling and solar heating are utilized. Furthermore, the device generates thermoelectric voltage even at night through radiative cooling which enables continuous energy harvesting throughout a day. Planar geometry and scalable fabrication process are advantageous for energy harvesting applications.

DOI： 10.1080/14686996.2021.1920820

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