Rotation of complex ions with ninefold hydrogen coordination studied by quasielastic neutron scattering and first-principles molecular dynamics calculations

大政 義典*; 高木 茂幸*; 戸嶋 健人*; 横山 凱乙*; 遠藤 亘*; 折茂 慎一*; 齋藤 寛之*; 山田 武*; 川北 至信; 池田 一貴*; et al.

Physical Review Research (Internet), 4(3), p.033215_1 - 033215_9, 2022/09

https://doi.org/10.1103/PhysRevResearch.4.033215

Quasielastic neutron scattering (QENS) and neutron powder diffraction of the complex transition metalhydrides LiMoH and LiNbH were measured in a temperature range of 10-300 K to study their structures and dynamics, especially the dynamics of the hydrogen atoms. These hydrides contain unusual ninefold H coordinated complex ions (MoH or NbH) and hydride ions (H). A QENS signal appeared 150 K due to the relaxation of H atoms. The intermediate scattering functions derived from the QENS spectra are well fitted by a stretched exponential function called the Kohlrausch-Williams-Watts functions with a small stretching exponent 0.3-0.4, suggesting a wide relaxation time distribution. The dependence of the elastic incoherent structure factor is reproduced by the rotational diffusion of MH (M = Mo or Nb) anions. The results are well supported by a van Hove analysis for the motion of H atoms obtained using first-principles molecular dynamics calculations. We conclude that the wide relaxation time distribution of the MH rotation is due to the positional disorder of the surrounding Li ions and a unique rotation with MH anion deformation (pseudorotation).

Evaluation of sample cell materials for aqueous solutions used in quasi-elastic neutron scattering measurements

富永 大輝*; 佐原 雅恵*; 川北 至信; 中川 洋; 山田 武*

Journal of Applied Crystallography, 54(6), p.1631 - 1640, 2021/12

https://doi.org/10.1107/S1600576721009687

For quasi-elastic neutron scattering (QENS) studies, sample cells made of pure or alloyed aluminum are frequently employed. Although the Al surface is protected by a passivating film, this film is not robust. Therefore, when the sample is an aqueous solution, chemical interactions between the Al surface and sample, promoted by corrosive entities such as chloride ions and certain conditions of pH, can compromise the integrity of the cell and interfere with the experiment. In this study, the corrosion susceptibilities of Al and its alloys were investigated by subjecting them to various treatments; the results were compared with those of other candidate materials with low chemical reactivity. This work showed that alloys with higher Al content and boehmite-coated surfaces are resistant to corrosion. In particular, for Al, the resistance is due to a reduction in the contact area achieved by reducing the surface roughness. QENS measurements of empty sample cells made of these materials revealed two results: (1) the profile of the cell fabricated with a copper-free Al alloy showed a minor dependence on the scattering vector magnitude and (2) reducing the real surface area of Al effectively suppresses its scattering intensity, while boehmite coating strengthens the scattering. Cells fabricated with Mo, Nb and single-crystal sapphire can be used as alternatives to Al because of their low scattering intensity and reduced dependence on .

Dynamics of water in a catalyst layer of a fuel cell by quasielastic neutron scattering

伊藤 華苗; 山田 武*; 篠原 朗大*; 高田 慎一; 川北 至信

Journal of Physical Chemistry C, 125(39), p.21645 - 21652, 2021/10

https://doi.org/10.1021/acs.jpcc.1c06014

The catalyst layer (CL) in polymer electrolyte fuel cells (PEFCs) plays a critical role in the performance of a PEFC. In this study, we investigate the water dynamics in the CL using quasielastic neutron scattering (QENS) and small-angle neutron scattering. The temperature dependence of the mean square displacement u shows that the freezing of water does not occur at a melting temperature in the Nafion thin film of the CL, suggesting that the water is confined in a smaller region than 15 . The QENS measurements established three kinds of water in the CL: immobile water tightly connected to a sulfonic group, water in a fast mode assigned to free diffusion restricted in a sphere, and water in a slow mode described by a jump diffusion model. Assuming that these three modes were independent, the number of water molecules in each mode was estimated. On discussing the structure and dynamics elucidated in the study, we finally conclude that the coupled model of the fast and slow modes is plausible for describing the diffusion of water confined in the thin Nafion film of the CL.

Nonmagnetic-magnetic transition and magnetically ordered structure in SmS

吉田 章吾*; 小山 岳秀*; 山田 陽彦*; 中井 祐介*; 上田 光一*; 水戸 毅*; 北川 健太郎*; 芳賀 芳範

Physical Review B, 103(15), p.155153_1 - 155153_5, 2021/04

https://doi.org/10.1103/PhysRevB.103.155153

SmS, a protopypical intermediate valence compound, has been studied by performing high-pressure nuclear magnetic resonance measurements. The observation of an additional signal at high pressure gives evidence of a magnetic phase transition. The cancellation of the hyperfined fields at the S site suggests a type-II antiferromagnetic structure.

Position-encoded automatic cell elevator for BL02, J-PARC MLF

富永 大輝*; 小林 誠*; 山田 武*; 松浦 直人*; 川北 至信; 笠井 聡*

JPS Conference Proceedings (Internet), 33, p.011095_1 - 011095_5, 2021/03

BB2019-1955.pdf:1.33MB

https://doi.org/10.7566/JPSCP.33.011095

トップローディング型冷凍機用の垂直移動型試料交換機が、J-PARC MLFのBL02に設置された中性子分光器の利用支援のために開発された。PEACEと名付けられたこの試料交換機は、中性子照射位置での試料位置の再現性を、PEEKと呼ぶ物質でできたガイドを利用して制御している。3つの試料位置でのバックグラウンド散乱のプロファイルの変化は1.6%以内であることが分かった。この結果は、垂直軸からの試料位置の偏差が0.3mmであることを考えると妥当である。

大規模土砂移動発生履歴の高精度復元に向けた埋没樹木の年代測定; 歴史時代に中部山岳地域で発生した事例

山田 隆二*; 木村 誇*; 苅谷 愛彦*; 佐野 雅規*; 對馬 あかね*; Li, Z.*; 中塚 武*; 國分 陽子; 井上 公夫*

砂防学会誌, 73(5), p.3 - 14, 2021/01

本研究では、深層崩壊発生履歴の高精度・高分解能復元に有効な試料採取および選定方法と年代値の適切な取扱について議論した。中部山岳地域で大規模な深層崩壊が発生した2箇所(ドンドコ沢岩石流れと大月川岩屑流)の土壌埋没樹木を試料とした事例研究を行った。年代測定は加速器質量分析計による放射性炭素年代測定法と酸素同位体比年輪年代測定法で行った。ドンドコ沢岩石流れによる堰止湖沼堆積物中から採取した試料は、887年の五畿七道地震に関連する年代値を示し、それ以前に他のイベントが存在した可能性も示唆した。一方、大月川岩屑流による崩壊堆積物から採取した試料年代値は特定の時期に集中しなかった。大規模土砂移動現象の発生年を正確に知るための試料として保存状態の良い大径樹幹や枝を用いることによって、大雨や大規模地震を示した古文書との対比も可能であることがわかった。

Enhancement of element production by incomplete fusion reaction with weakly bound deuteron

Wang, H.*; 大津 秀暁*; 千賀 信幸*; 川瀬 頌一郎*; 武内 聡*; 炭竃 聡之*; 小山 俊平*; 櫻井 博儀*; 渡辺 幸信*; 中山 梓介; et al.

Communications Physics (Internet), 2(1), p.78_1 - 78_6, 2019/07

https://doi.org/10.1038/s42005-019-0165-1

陽子(あるいは中性子)過剰核の効率的な生成経路を探索することは、原子核反応研究の主な動機のひとつである。本研究では、Pdに対する核子当たり50MeVの陽子および重陽子入射による残留核生成断面積を逆運動学法によって測定した。その結果、重陽子入射ではAgやPd同位体の生成断面積が大きくなることを実験的に示した。また、理論計算による解析から、この生成断面積の増大は重陽子の不完全融合反応に起因することを示した。これらの結果は、陽子過剰核の生成において重陽子のような弱束縛核の利用が有効であることを示すものである。

Micro-PIXE analysis study of ferrite products synthesized from simulated radioactive liquid waste containing chemical hazardous elements

阿部 智久; 嶋崎 竹二郎; 大杉 武史; 中澤 修; 山田 尚人*; 百合 庸介*; 佐藤 隆博*

QST-M-16; QST Takasaki Annual Report 2017, P. 140, 2019/03

http://id.nii.ac.jp/1657/00074822/

フェライト処理による有害元素の固定化技術の開発のため、固定化性能に影響を及ぼす可能性のある陰イオンを分析する必要がある。本研究では、異なる金属元素を複数の鉄源を用いて合成したフェライトのマイクロPIXE分析を行い、合成したフェライトの違いを組成の観点から明らかにすることを試みた。元素のマッピングデータとピクセルごとの信号強度の相関をとった結果、Agでは、陰イオンの分布がいずれも0に近い部分に分布していた。また、Pbでは横軸に広がった分布となっており、Crでは縦軸に広がった分布となった。今回の結果では、陰イオンの種類ではなく、対象とする金属元素により分布の相関に違いがあることがわかった。

Neutron scattering studies on short- and long-range layer structures and related dynamics in imidazolium-based ionic liquids

根本 文也*; 古府 麻衣子; 長尾 道弘*; 大石 一城*; 高田 慎一; 鈴木 淳市*; 山田 武*; 柴田 薫; 上木 岳士*; 北沢 侑造*; et al.

Journal of Chemical Physics, 149(5), p.054502_1 - 054502_11, 2018/08

https://doi.org/10.1063/1.5037217

Alkyl-methyl-imidazolium ionic liquids CmimX (: alkyl-carbon number, X: anion) have short-range layer structures consisting of ionic and neutral (alkylchain) domains. To investigate the temperature dependences of the interlayer, interionic group, and inter-alkylchain correlations, we have measured the neutron diffraction (ND) of CmimPF ( = 16, 9.5, 8). The quasielastic neutron scattering (QENS) of C16mimPF was also measured to study the dynamics of each correlation. C16mimPF shows a first-order transition between the liquid (L) and liquid crystalline (LC) phases at = 394 K. C8mimPF exhibits a glass transition at = 200 K. C9.5mimPF has both transitions at = 225 K and = 203 K. In the ND experiments, all samples exhibit three peaks corresponding to the correlations mentioned above. The widths of the interlayer peak at ca. 0.2 changed drastically at the L-LC transitions, while the interionic peaks at ca. 1 exhibited a small jump at . The peak position and area of the three peaks did not change much at the transition. The structural changes were minimal at . The QENS experiments demonstrated that the relaxation time of the interlayer motion increased tenfold at , while those of other motions were monotonous in the whole temperature region. The structural and dynamical changes are characteristic of the L-LC transition in imidazolium-based ionic liquids.

Diffusion behavior of methanol molecules confined in cross-linked phenolic resins studied using neutron scattering and molecular dynamics simulations

首藤 靖幸*; 和泉 篤士*; 萩田 克美*; 山田 武*; 柴田 薫; 柴山 充弘*

Macromolecules, 51(16), p.6334 - 6343, 2018/08

https://doi.org/10.1021/acs.macromol.8b00535

The dynamics of methanol confined in highly cross-linked phenolic resins was investigated using incoherent quasielastic neutron scattering (QENS) and atomistic molecular dynamics (MD) simulations. The QENS analysis for adeuterated phenolic resin and both deuterated and nondeuterated methanol indicated the presence of resin dynamics induced by methanol invasion and confined diffusion of the methanol molecules. QENS results suggested that methanol had a diffusion coefficient of 1.6 10 cm/s, which is 1 order of magnitude smaller than the bulk value (2.3 10 cm/s. The MD trajectories also showed that the methanol diffusion was limited by the resin network, consistent with QENS results in terms of the diffusion coefficient and diffusion-like behavior.