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

Omasa, Yoshinori*; Takagi, Shigeyuki*; Toshima, Kento*; Yokoyama, Kaito*; Endo, Wataru*; Orimo, Shinichi*; Saito, Hiroyuki*; Yamada, Takeshi*; Kawakita, Yukinobu; Ikeda, Kazutaka*; et al.

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

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

Nanometric fluctuations of sound velocity in alkali borate glasses and fragility of respective melts

Kojima, Seiji*; Novikov, V. N.*; Kofu, Maiko; Yamamuro, Osamu*

Physica Status Solidi (B), 257(11), p.2000073_1 - 2000073_6, 2020/11

https://doi.org/10.1002/pssb.202000073

Dynamics of atomic hydrogen in palladium probed by neutron spectroscopy

Kofu, Maiko; Yamamuro, Osamu*

Journal of the Physical Society of Japan, 89(5), p.051002_1 - 051002_12, 2020/05

https://doi.org/10.7566/JPSJ.89.051002

The behavior of hydrogen in metals has attracted much attention in fundamental and applied research areas for many decades. Among metals, palladium is remarkable in that it can absorb large quantities of hydrogen, and hydrogen atoms are highly mobile in the fcc Pd lattice. The dynamics of hydrogen in Pd have been investigated by means of neutron spectroscopy which is the best tool to provide insights into microscopic dynamics of hydrogen atoms. In this article, we review recent and historical neutron scattering works to facilitate the latest understanding of the hydrogen dynamics in bulk and nanometer-sized Pd hydrides.

Universality and structural implications of the Boson peak in Proteins

Nakagawa, Hiroshi; Jochi, Yasumasa*; Kitao, Akio*; Yamamuro, Osamu*; Kataoka, Mikio*

Biophysical Journal, 117(2), p.229 - 238, 2019/07

https://doi.org/10.1016/j.bpj.2019.06.007

Softness and rigidity of proteins are reflected in the structural dynamics, which are in turn affected by the environment. The characteristic low-frequency vibrational spectrum of a protein, known as boson peak, is an indication of the structural rigidity of the protein at cryogenic temperature or dehydrated conditions. In this paper, the effect of hydration, temperature, and pressure on the boson peak and volumetric properties of a globular protein are evaluated by using inelastic neutron scattering and molecular dynamics simulation. Hydration, pressurization, and cooling shift the boson peak position to higher energy and depress the peak intensity and decreases the protein and cavity volumes, although pressure hardly affects the boson peak of the fully hydrated protein. A decrease of each volume means the increase of rigidity, which is the origin of the boson peak shift. The boson peak profile can be predicted by the total cavity volume. This prediction is effective for the evaluation of the net quasielastic scattering of incoherent neutron scattering spectra when the boson peak cannot be distinguished experimentally because of a strong contribution from quasielastic scattering.

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

Nemoto, Fumiya*; Kofu, Maiko; Nagao, Michihiro*; Oishi, Kazuki*; Takata, Shinichi; Suzuki, Junichi*; Yamada, Takeshi*; Shibata, Kaoru; Ueki, Takeshi*; Kitazawa, Yuzo*; et al.

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

https://doi.org/10.1063/1.5037217

Mode-distribution analysis of quasielastic neutron scattering and application to liquid water

Kikuchi, Tatsuya; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Yamamuro, Osamu*; Kofu, Maiko*; Kawakita, Yukinobu; Suzuya, Kentaro; Nakamura, Mitsutaka; Arai, Masatoshi

Physical Review E, 87(6), p.062314_1 - 062314_8, 2013/06

https://doi.org/10.1103/PhysRevE.87.062314

A quasi-elastic neutron scattering (QENS) experiment is a particular technique that endeavors to define a relationship between time and space for the diffusion dynamics of atoms and molecules. However, in most cases, analyses of QENS data are model dependent. We have developed a new method for processing QENS data without a specific model, wherein all modes can be described as combinations of the relaxations based on the exponential law. By this method, we can obtain a new distribution function, , which we call the mode distribution function (MDF), to represent the number of relaxation modes and distributions of the relaxation times in the modes. The deduction of MDF is based on the maximum entropy method. We report the first application to experimental data of liquid water. In addition to the two known modes, the existence of a new relaxation mode of water molecules with an intermediate time scale has been discovered.

Dynamics of liquid polymer alkylated polythiophene

Nirei, Masami; Shinohara, Akira*; Nakanishi, Takashi*; Kawamura, Seiko; Akiba, Hiroshi*; Yamamuro, Osamu*; Kofu, Maiko

no journal, , 

Mode distribution analysis; A New method for model-free analysis on quasi-elastic neutron scattering

Kikuchi, Tatsuya; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Yamamuro, Osamu*; Kofu, Maiko*; Kawakita, Yukinobu; Suzuya, Kentaro; Nakamura, Mitsutaka; Arai, Masatoshi

no journal, , 

In generally so far, analysis of quasi-elastic neutron scattering spectra needs some mathematical models in its process, and hence the obtained result is a model dependent. In this context, we are trying to develop new model-free analysis method which we call as mode distribution analysis. In this method, we supposed that all modes can be described as combinations of the relaxations based on the exponential law. In the result of the analysis, we can obtain an intensity distribution for HWHM of Loretzian. This function can show the number of modes and distributions of the relaxation times in the modes and we call it as mode distribution function (MDF). In this new approach, we can obtain the MDF by using the maximum entropy method (MEM). We will also report a first application of our method to HO at RT. The measurement was carried out on AMATERAS spectrometer installed at J-PARC. In the result, we discover a motion of water molecule, which has not reported by earlier studies.

Dynamics of atomic hydrogen in bulk and nanocrystalline palladium

Kofu, Maiko; Hashimoto, Naoki*; Akiba, Hiroshi*; Kobayashi, Hirokazu*; Kitagawa, Hiroshi*; Tyagi, M.*; Faraone, A.*; Copley, J.*; Lohstorh, W.*; Iida, Kazuki*; et al.

no journal, , 

no abstracts in English

Neutron scattering study of a magnetic ionic liquid CmimFeCl

Kofu, Maiko; Watanuki, Ryuta*; Sakakibara, Toshiro*; Kawamura, Seiko; Nakajima, Kenji; Ueki, Takeshi*; Akutsu, Kazuhiro*; Yamamuro, Osamu*

no journal, , 

Ionic liquids (ILs) have been in the spotlight due to their unique and interesting properties. It is remarkable that their physicochemical properties are controlled by varying cations and anions. Magnetic IL is an example. The first discovered magnetic IL CmimFeCl is easily vitrified upon cooling and also crystallized by annealing. Interestingly, an antiferromagnetic transition occurs at 2.3 K in the crystalline state while spin-glass behavior is observed below 0.45 K (= ) in the glassy state. Our inelastic neutron scattering experiments have demonstrated that the glassy CmimFeCl exhibits a broad and non-dispersive excitation, while the crystal displays spin-wave excitations. The excitation spectrum in the glass state is scaled by the Bose population factor below , which is highly reminiscent of "boson peak" commonly observed in structural glasses. We guess that, since there is no periodicity in structural glasses, magnons hardly propagate through magnetic medium and are localized.