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Mictomagnetism and suppressed thermal conduction of the prototype high-entropy alloy CrMnFeCoNi

Yang, J.*; Ren, W.*; Zhao, X.*; 菊地 龍弥*; Miao, P.*; 中島 健次; Li, B.*; Zhang, Z.*

Journal of Materials Science and Technology, 99, p.55 - 60, 2022/02

物性測定と中性子散乱を組み合わせることにより、面心立方高エントロピー合金CrMnFeCoNiの磁気および熱輸送特性を調べた。DCおよびAC帯磁率は、温度領域全体で反強磁性および強磁性相互作用が共存する常磁性挙動を示し、それぞれ、常磁性から反強磁性への遷移、反強磁性から強磁性への遷移、およびスピン凍結に対応して、約80, 50、および20Kで3つの異常が見られる。電気伝導率と熱伝導率はNiに比べて大幅に低下しており、格子熱伝導率の温度依存性はガラスのようなプラトーを示す。非弾性中性子散乱測定は弱い非調和性を示唆し、熱輸送は欠陥散乱によって支配されると思われる。


Origin of magnetovolume effect in a cobaltite

Miao, P.*; Tan, Z.*; Lee, S. H.*; 石川 喜久*; 鳥居 周輝*; 米村 雅雄*; 幸田 章宏*; 小松 一生*; 町田 真一*; 佐野 亜沙美; et al.

Physical Review B, 103(9), p.094302_1 - 094302_18, 2021/03

 被引用回数:0 パーセンタイル:0(Materials Science, Multidisciplinary)

層状ペロブスカイトPrBaCo$$_{2}$$O$$_{5.5}$$は、熱膨張のない複合材料を作るために必要な負の熱膨張(NTE)を示す。NTEは、自発的な磁気秩序と密接に関連していることがわかっていた(磁気体積効果: MVE)。今回、われわれは、PrBaCo$$_{2}$$O$$_{5.5}$$の連続的な磁気体積効果が、本質的には不連続であり、大きな体積を持つ反強磁性絶縁体(AFILV)から、小さな体積をもつ強磁性卑絶縁体(FLISV)への磁気電気的相転移に起因することを明らかにした。また、磁気電気効果(ME)は、温度,キャリアドーピング,静水圧,磁場などの複数の外部刺激に対して高い感度を示した。これは、これまでよく知られている対称性の破れを伴う巨大磁気抵抗やマルチフェロイック効果などのMEとは対照的であり、輝コバルト鉱のMEは同一の結晶構造で起こる。われわれの発見は、MEとNTEを実現するための新しい方法を示しており、それは新しい技術に応用されるかもしれない。


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

 被引用回数:6 パーセンタイル:75.63(Chemistry, Multidisciplinary)



Crystal structures of highly hole-doped layered perovskite nickelate Pr$$_{2-x}$$Sr$$_{x}$$NiO$$_{4}$$ studied by neutron diffraction

梶本 亮一; 中島 健次; 藤田 全基*; 石角 元志*; 鳥居 周輝*; 石川 喜久*; Miao, P.*; 神山 崇*

Journal of the Physical Society of Japan, 88(11), p.114602_1 - 114602_6, 2019/11

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

A high-resolution time-of-flight powder neutron diffraction study of the layered nickel oxide Pr$$_{2-x}$$Sr$$_{x}$$NiO$$_{4}$$ with $$x = 0.7$$ and $$0.9$$ was performed to characterize the crystal structures of these highly hole-doped nickelates. For the sample with $$x = 0.7$$, the Ni-O bond lengths decrease uniformly with decreasing temperature, and the atomic displacement parameters are similar to those for $$x = 1/3$$. In contrast, for the sample with $$x = 0.9$$, the out-of-plane Ni-O bond length shows a sharp thermal contraction in the high-temperature region, which is suggestive of changes in the orbital occupation accompanied by the development of checkerboard-type charge correlations. Furthermore, the $$x = 0.9$$ sample is characterized by a large atomic displacement parameter for the apical O atoms along the out-of-plane direction, which is interpreted as the existence of two types of Ni$$^{3+}$$ sites with different orbital occupancies. The distinct difference between the $$x = 0.9$$ sample and the lower-concentration compounds should be related to the development of checkerboard-type charge ordering in the metallic matrix and possible orbital ordering at the Ni$$^{3+}$$ sites at $$x sim 1$$ in the hole-doped layered nickel oxides.


Atomically dispersed Pt on the surface of Ni particles; Synthesis and catalytic function in hydrogen generation from aqueous ammonia-borane

Li, Z.*; He, T.*; 松村 大樹; Miao, S.*; Wu, A.*; Liu, L.*; Wu, G.*; Chen, P.*

ACS Catalysis, 7(10), p.6762 - 6769, 2017/10

 被引用回数:102 パーセンタイル:96.66(Chemistry, Physical)

We report herein that the single-atom alloy (SAA) made of atomically dispersed Pt on the surface of Ni particles (Pt is surrounded by Ni atoms) exhibits improved catalytic activity on the hydrolytic dehydrogenation of ammonia-borane, a promising hydrogen storage method for onboard applications. Specifically, an addition of 160 ppm of Pt leads to ca. 3-fold activity improvement in comparison to that of pristine Ni/CNT catalyst. The turnover frequency based on the isolated Pt is 12000 mol$$_{rm{H}2}$$ mol$$_{rm{Pt}}$$$$^{-1}$$ min$$^{-1}$$, which is about 21 times the value of the best Pt-based catalyst ever reported. Our simulation results indicate that the high activity achieved stems from the synergistic effect between Pt and Ni, where the negatively charged Pt (Pt$$^{delta -}$$) and positively charged Ni (Ni$$^{delta +}$$) in the Pt-Ni alloy are prone to interact with H and OH of H$$_{2}$$O molecules, respectively, leading to an energetically favorable reaction pathway.


Colossal negative thermal expansion induced by magnetic phase competition on frustrated lattices in Laves phase compound (Hf,Ta)Fe$$_2$$

Li, B.; Luo, X. H.*; Wang, H.*; Ren, W. J.*; Yano, S.*; Wang, C.-W.*; Gardner, J. S.*; Liss, K.-D.*; Miao, P.*; Lee, S.-H.*; et al.

Physical Review B, 93(22), p.224405_1 - 224405_6, 2016/06

 被引用回数:33 パーセンタイル:83.88(Materials Science, Multidisciplinary)

Competition between ferromagnetic and antiferromagnetic phases on frustrated lattices in hexagonal Laves phase compound Hf$$_{0.86}$$Ta$$_{0.14}$$Fe$$_2$$ is investigated by using neutron diffraction as a function of temperature and magnetic fields and density-functional-theory calculations. At 325 K, the compound orders into the 120$$^{circ}$$ frustrated antiferromagnetic state with well-reduced magnetic moment and an in-plane lattice contraction simultaneously sets in. With further cooling down, however, the accumulated distortion in turn destabilizes this susceptible frustrated structure. The frustration is completely relieved at 255 K when the first-order transition to the ferromagnetic state takes place, where a colossal negative volumetric thermal expansion, $$-123 times 10^{-6}$$/K, is obtained. Meanwhile, the antiferromagnetic state can be suppressed by few Tesla magnetic fields, which results in a colossal positive magnetostriction. Such delicate competition is attributed to the giant magnetic fluctuation inherent in the frustrated antiferromagnetic state. Therefore, the magnetoelastic instability is approached even under a small perturbation.


Bipartite magnetic parent phases in the iron oxypnictide superconductor

平石 雅俊*; 飯村 壮史*; 小嶋 健児*; 山浦 淳一*; 平賀 晴弘*; 池田 一貴*; Miao, P.*; 石川 喜久*; 鳥居 周輝*; 宮崎 正範*; et al.

Nature Physics, 10(4), p.300 - 303, 2014/04

 被引用回数:94 パーセンタイル:96.38(Physics, Multidisciplinary)

High-temperature (high-$$T_{rm c}$$) superconductivity appears as a consequence of the carrier-doping of an undoped parent compound exhibiting antiferromagnetic order; thereby, ground-state properties of the parent compound are closely relevant to the superconducting state. On the basis of the concept, a spin-fluctuation has been addressed as an origin of pairing of the superconducting electrons in cuprates. Whereas, there is growing interest in the pairing mechanism such as an unconventional spin-fluctuation or an advanced orbital-fluctuation due to the characteristic multi-orbital system in iron-pnictides. Here, we report the discovery of an antiferromagnetic order as well as a unique structural transition in electron-overdoped LaFeAsO$$_{1-x}$$H$$_x$$ ($$x sim 0.5$$), whereby another parent phase was uncovered, albeit heavily doped. The unprecedented two-dome superconducting phases observed in this material can be interpreted as a consequence of the carrier-doping starting from the original at $$x sim 0$$ and advanced at $$x sim 0.5$$ parent phases toward the intermediate region. The bipartite parent phases with distinct physical properties in the second magnetic phase provide us with an interesting example to illustrate the intimate interplay among the magnetic interaction, structural change and orbital degree of freedom in iron-pnictides.


Neutron and X-ray total scattering study on superionic thermoelectric AgCrSe$$_{2}$$

Li, B.; Feygenson, M.*; 尾原 幸治*; Zhang, Q.*; Vaknin, D.*; 山田 武*; Miao, P.*; 神山 崇*; 川北 至信

no journal, , 

Very recently, superionic AgCrSe$$_{2}$$ was reported as a new thermoelectric material because of its record-low thermal conductivity. To understand the origin of such low thermal conductivity, we measured the powder sample of AgCrSe$$_{2}$$ at NOMAD of Spallation Neutron Source and BL04B2 of SPring-8. The diffraction data and pair distribution functions were obtained as a function of temperature from both neutron and X-ray experiments. In this presentation, I will report the crystal structure and local structure of this compound. This compound undergoes a second-order transition at 170$$^{circ}$$C from R-3m to R3m and can be described by 2D Ising model. The lattice constant c and Debye-Waller factor U11 of Ag exhibit significant change at the transition. The weaker Ag-Se bonding is seen from the pair distribution functions above this transition. At the same time, the pair distribution function beyond $$sim$$ 80 Angstrom becomes very different above this transition. This implies there is mesoscale inhomogenousity and might be related to the low thermal conductivity.



梶本 亮一; 中島 健次; 藤田 全基*; 石角 元志*; 鳥居 周輝*; 石川 喜久*; Miao, P.*; 神山 崇*

no journal, , 

ホールがドープされた層状ペロブスカイトNi酸化物R$$_{2-x}$$Sr$$_{x}$$NiO$$_{4}$$はホール濃度$$x<1/2$$でストライプ型の電荷・磁気秩序を示し、$$x>1/2$$では市松模様型の電荷秩序を広い濃度範囲で示すことが知られている。$$x>1/2$$の高ホール濃度領域ではホールが面間の軌道に入ることで面内の市松模様型電荷秩序を保つと考えられ、$$x=1$$付近で金属に転移しても、依然として市松模様型電荷秩序の相関が強く残った異常金属状態となっていると考えられている。そこで、$$x>1/2$$の高ホール濃度領域における電荷・軌道状態を結晶構造の観点から探るため、高分解能中性子回折による結晶構造解析を行った。試料はPr$$_{2-x}$$Sr$$_{x}$$NiO$$_{4}$$$$x=0.7$$と0.9の粉末試料を用い、中性子回折実験はMLF BL08のSuperHRPDにて行った。$$x=0.7$$では格子定数, Ni-O結合長, 原子変位パラメータ共に滑らかな温度変化を示し、その変化の様子は低ホール濃度の$$x=1/3$$で報告されているものと同程度であった。一方、$$x=0.9$$では、NiO$$_{6}$$八面体の頂点方向のNi-O結合長が高温領域で大きな熱収縮を示し、さらに、頂点酸素の面間方向の原子変位パラメータが、他の組成の試料に比べて特に大きな値を示すことを見いだした。本発表では、この$$x=0.9$$における特異な構造的特徴を電荷の伝導性、Ni$$^{3+}$$サイト上の軌道状態と関連づけて考察する。

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