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論文

Crystal-liquid duality driven ultralow two-channel thermal conductivity in -MgAgSb

Li, J.*; Li, X.*; Zhang, Y.*; Zhu, J.*; Zhao, E.*; 古府麻衣子; 中島健次; Avdeev, M.*; Liu, P.-F.*; Sui, J.*; et al.

Applied Physics Reviews (Internet), 11(1), p.011406_1 - 011406_8, 2024/03

被引用回数：0 パーセンタイル：0.01(Physics, Applied)

The desire for intrinsically low lattice thermal conductivity () in thermoelectrics motivates numerous efforts on understanding the microscopic mechanisms of heat transport in solids. Here, based on theoretical calculations, we demonstrate that -MgAgSb hosts low-energy localized phonon bands and avoided crossing of the rattler modes, which coincides with the inelastic neutron scattering result. Using the two-channel lattice dynamical approach, we find, besides the conventional contribution (70% at 300 K) from particlelike phonons propagating, the coherence contribution dominated by the wavelike tunneling of phonons accounts for 30% of total at 300 K. By considering dual contributions, our calculated room-temperature of 0.64 Wm $^{-1}$ K $^{-1}$ well agrees with the experimental value of 0.63 Wm $^{-1}$ K $^{-1}$ . More importantly, our computations give a nonstandard $kappa_L propto T^{-0.61}$ dependence, perfectly explaining the abnormal temperature-trend of $sim T^{-0.57}$ in experiment for -MgAgSb. By molecular dynamics simulation, we reveal that the structure simultaneously has soft crystalline sublattices with the metavalent bonding and fluctuating liquid-like sublattices with thermally induced large amplitude vibrations. These diverse forms of chemical bonding arouse mixed part-crystal part-liquid state, scatter strongly heat-carrying phonons, and finally produce extremely low . The fundamental research from this study will accelerate the design of ultralow- materials for energy-conversion applications.

論文

Extreme phonon anharmonicity underpins superionic diffusion and ultralow thermal conductivity in argyrodite Ag $_{8}$ SnSe $_{6}$

Ren, Q.*; Gupta, M. K.*; Jin, M.*; Ding, J.*; Wu, J.*; Chen, Z.*; Lin, S.*; Fabelo, O.*; Rodriguez-Velamazan, J. A.*; 古府麻衣子; et al.

Nature Materials, 22, p.999 - 1006, 2023/05

https://doi.org/10.1038/s41563-023-01560-x

被引用回数：21 パーセンタイル：99.22(Chemistry, Physical)

Ultralow thermal conductivity and fast ionic diffusion endow superionic materials with excellent performance both as thermoelectric converters and as solid-state electrolytes. Yet the correlation and interdependence between these two features remain unclear owing to a limited understanding of their complex atomic dynamics. Here we investigate ionic diffusion and lattice dynamics in argyrodite Ag $_{8}$ SnSe $_{6}$ using synchrotron X-ray and neutron scattering techniques along with machine-learned molecular dynamics. We identify a critical interplay of the vibrational dynamics of mobile Ag and a host framework that controls the overdamping of low-energy Ag-dominated phonons into a quasi-elastic response, enabling superionicity. Concomitantly, the persistence of long-wavelength transverse acoustic phonons across the superionic transition challenges a proposed 'liquid-like thermal conduction' picture. Rather, a striking thermal broadening of low-energy phonons, starting even below 50 K, reveals extreme phonon anharmonicity and weak bonding as underlying features of the potential energy surface responsible for the ultralow thermal conductivity ( 0.5 Wm $^{-1}$ K $^{-1}$ ) and fast diffusion. Our results provide fundamental insights into the complex atomic dynamics in superionic materials for energy conversion and storage.

論文

Two-dimensional quantum universality in the spin-1/2 triangular-lattice quantum antiferromagnet Na $_{2}$ BaCo(PO $_{4}$ ) $_{2}$

Sheng, J.*; Wang, L.*; Candini, A.*; Jiang, W.*; Huang, L.*; Xi, B.*; Zhao, J.*; Ge, H.*; Zhao, N.*; Fu, Y.*; et al.

Proceedings of the National Academy of Sciences of the United States of America, 119(51), p.e2211193119_1 - e2211193119_9, 2022/12

https://doi.org/10.1073/pnas.2211193119

被引用回数：3 パーセンタイル：28(Multidisciplinary Sciences)

Although considerable progress has been made in the theoretical understanding of the low-dimensional frustrated quantum magnets, experimental realizations of a well-established scaling analysis are still scarce. This is particularly true for the two-dimensional antiferromagnetic triangular lattices. Owing to the small exchange strength, the newly discovered compound Na $_{2}$ BaCo(PO $_{4}$ ) $_{2}$ provides a rare opportunity for clarifying the quantum criticality in an ideal triangular lattice with quantum spin S=1/2. In addition to the establishment of the complete phase diagrams, the spin Hamiltonian with a negligible interplane interaction has been determined through the spin wave dispersion in the polarized state, which is consistent with the observation of a two-dimensional quantum critical point with the Bose-Einstein condensation of diluted free bosons.

論文

Grain orientation dependence of deformation microstructure evolution and mechanical properties in face-centered cubic high/medium entropy alloys

吉田周平*; Fu, R.*; Gong, W.; 池内琢人*; Bai, Y.*; Feng, Z.*; Wu, G.*; 柴田曉伸*; Hansen, N.*; Huang, X.*; et al.

IOP Conference Series; Materials Science and Engineering, 1249, p.012027_1 - 012027_6, 2022/08

https://doi.org/10.1088/1757-899X/1249/1/012027

被引用回数：0 パーセンタイル：0.83(Metallurgy & Metallurgical Engineering)

This study revealed characteristics of the deformation behavior in high/medium entropy alloys (HEAs/MEAs) with face-centered cubic (FCC) structure. A Co $_{60}$ Ni $_{40}$ alloy and a Co $_{20}$ Cr $_{40}$ Ni $_{40}$ MEA having low and high friction stresses (fundamental resistance to dislocation glide in solid solutions), respectively, but similar in other properties, including their stacking fault energy and grain sizes, were compared. The MEA exhibited a higher yield strength and work-hardening ability than those in the Co $_{60}$ Ni $_{40}$ alloy at room temperature. Deformation microstructures of the Co $_{60}$ Ni $_{40}$ alloy were composed of coarse dislocation cells (DCs) in most grains, and a few deformation twins (DTs) formed in grains with tensile axis (TA) nearly parallel to 111. In the MEA, three microstructure types were found depending on the grain orientations: (1) fine DCs developed in TA//100-oriented grains; (2) planar dislocation structures (PDSs) formed in grains with other orientations; and (3) dense DTs adding to the PDSs developed in TA//111-oriented grains. The results imply difficulty in cross-slip of screw dislocations and dynamic recovery in the MEA, leading to an increase in the dislocation density and work-hardening rate. Our results suggest that FCC high-alloy systems with high friction stress inherently develop characteristic deformation microstructures advantageous for achieving high strength and large ductility.

論文

Temporally decoherent and spatially coherent vibrations in metal halide perovskites

Zhang, D.*; Hu, X.*; Chen, T.*; Abernathy, D. L.*; 梶本亮一; 中村充孝; 古府麻衣子; Foley, B. J.*; Yoon, M.*; Choi, J. J.*; et al.

Physical Review B, 102(22), p.224310_1 - 224310_10, 2020/12

https://doi.org/10.1103/PhysRevB.102.224310

被引用回数：4 パーセンタイル：26.53(Materials Science, Multidisciplinary)

The long carrier lifetime and defect tolerance in metal halide perovskites (MHPs) are major contributors to the superb performance of MHP optoelectronic devices. Large polarons were reported to be responsible for the long carrier lifetime. Yet microscopic mechanisms of the large polaron formation, including the so-called phonon melting, are still under debate. Here, time-of-flight inelastic neutron scattering experiments and first-principles density-functional theory calculations were employed to investigate the lattice vibrations (or phonon dynamics) in methylammonium lead iodide, a prototypical example of MHPs. Our findings are that optical phonons lose temporal coherence gradually with increasing temperature which vanishes at the orthorhombic-to-tetragonal structural phase transition. Surprisingly, however, we found that the spatial coherence is still retained throughout the decoherence process. We argue that the temporally decoherent and spatially coherent vibrations contribute to the formation of large polarons in this metal halide perovskite.

論文

Distance-selected topochemical dehydro-diels-alder reaction of 1,4-Diphenylbutadiyne toward crystalline graphitic nanoribbons

Zhang, P.*; Tang, X.*; Wang, Y.*; Wang, X.*; Gao, D.*; Li, Y.*; Zheng, H.*; Wang, Y.*; Wang, X.*; Fu, R.*; et al.

Journal of the American Chemical Society, 142(41), p.17662 - 17669, 2020/10

https://doi.org/10.1021/jacs.0c08274

被引用回数：21 パーセンタイル：74.59(Chemistry, Multidisciplinary)

固体トポケミカル重合(SSTP)は機能的な結晶性高分子材料を合成するための有望な方法であるが、溶液中で起こるさまざまな反応とは対照的に、非常に限られたタイプのSSTP反応しか報告されていない。ディールス・アルダー(DA)および脱水素-DA(DDA)反応は、溶液中で六員環を作るための教科書的反応であるが、固相合成ではほとんど見られない。本研究では、固体の1,4-ジフェニルブタジイン(DPB)を10-20GPaに加圧することで、フェニル基がジエノフィルとして、DDA反応することを複数の最先端の手法を用いて明らかにした。臨界圧力での結晶構造は、この反応が「距離選択的」であることを示している。つまり、フェニルとフェニルエチニル間の距離3.2は、DDA反応は起こせるが、他のDDAや1,4-付加反応で結合を形成するには長すぎる。回収された試料は結晶性の肘掛け椅子型のグラファイトナノリボンであるため、今回の研究結果は、原子スケールの制御で結晶質炭素材料を合成するための新しい道を開く。

論文

Ultralow thermal conductivity from transverse acoustic phonon suppression in distorted crystalline -MgAgSb

Li, X.*; Liu, P.-F.*; Zhao, E.*; Zhang, Z.*; Guide, T.*; Le, M. D.*; Avdeev, M.*; 池田一貴*; 大友季哉*; 古府麻衣子; et al.

Nature Communications (Internet), 11, p.942_1 - 942_9, 2020/02

https://doi.org/10.1038/s41467-020-14772-5

被引用回数：36 パーセンタイル：90.35(Multidisciplinary Sciences)

高性能の熱電材料実現には低熱伝導率が必要であり、その機構としてはフォノンの非調和によるもの、あるいは、結晶構造の動的な乱れによるフォノンの散乱によるものがあげられ、どちらも中性子散乱でその現象が明らかにされている。我々は中性子散乱と第一原理計算を組み合わせ、-MgAgSbにおいて、静的な結晶構造の乱れとフォノンの非調和性が組み合わされて極端に低い熱伝導率が実現されているということを見いだしたので、これを報告する。

報告書

Comparison of HTGR fuel design, manufacture and quality control methods between Japan and China

Fu, X.*; 高橋昌史; 植田祥平; 沢和弘

JAERI-Tech 2002-049, 35 Pages, 2002/05

JAERI-Tech-2002-049.pdf:3.01MB

日本のHTTR用初装荷燃料は1995年より原子燃料工業(株)で製造を開始し、HTTRは1998年に臨界となった。一方、中国では清華大学のINET(Institute of Nuclear Energy Technology)にて10MWの高温ガス炉(HTR-10)建設と並行して、燃料製造が進められた。この結果、HTR-10は2000年12月に臨界に達した。日本のHTTRと中国のHTR-10では燃料型式がそれぞれピンインブロック型,ペブルベッド型と異なっているが、いずれもTRISO粒子である被覆燃料粒子のように似通った部分もある。本報は日本と中国における燃料設計の違い,製造方法の違い,品質保証方法の違いを比較検討し、まとめたものである。

口頭

Difference of results obtained with high and low Andersen sampler respectively in the research of atmospheric aerosols

Fu, F.; 渡部和男; Wu, Y.*; Xiao, L.*; Xu, X.*; 篠原伸夫

no journal, ,

大気中のエアロゾルを研究する際に、通常サンプラーを用いてエアロゾルをフィルターに採集し研究する。ハイボリュームとローボリュームアンダーセンサンプラーはエアロゾルの採集によく利用される二種類のサンプラーである。しかし、この二種類のサンプラーから得られた結果は必ず一致することではない。本研究では、この二種類のサンプラーを用いて大気中のエアロゾル濃度,エアロゾル濃度の季節変化と粒度分布,化学成分の季節変化と粒度分布を詳しく研究したうえ、両サンプラーによるの結果差異を詳しく調べ、その原因について議論した。

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