Anomalous behavior of liquid molecules near solid nanoparticles; Novel interpretation on thermal conductivity enhancement in nanofluids

Hashimoto, Shunsuke*; Yamaguchi, Satoshi*; Harada, Masashi*; Nakajima, Kenji; Kikuchi, Tatsuya*; Oishi, Kazuki*

Journal of Colloid and Interface Science, 638, p.475 - 486, 2023/05

https://doi.org/10.1016/j.jcis.2023.01.101

Recently, it has been reported that anomalous improvement in the thermal conductivity of nanofluid composed of base liquids and dispersed solid nanoparticles, compared to the theoretically predicted value calculated from the particle fraction. Generally, the thermal conductivity values of gases and liquids are dominated by the mean free path of the molecules during translational motion. Herein, we present solid evidence showing the possible contribution of the vibrational behavior of liquid molecules around nanoparticles to increasing these thermal conductivities.

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

Yang, J.*; Ren, W.*; Zhao, X.*; Kikuchi, Tatsuya*; Miao, P.*; Nakajima, Kenji; Li, B.*; Zhang, Z.*

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

https://doi.org/10.1016/j.jmst.2021.04.077

High-entropy alloys are characteristic of extensive atomic occupational disorder on high-symmetric lattices, differing from traditional alloys. Here, we investigate magnetic and thermal transport properties of the prototype face-centered-cubic high-entropy alloy CrMnFeCoNi by combining physical properties measurements and neutron scattering. Direct-current (dc) and alternating-current (ac) magnetizations measurements indicate a mictomagnetic behavior with coexisting antiferromagnetic and ferromagnetic interactions in the entire temperature region and three anomalies are found at about 80, 50, and 20 K, which are related to the paramagnetic to antiferromagnetic transition, the antiferromagnetic to ferromagnetic transition, and the spin freezing, respectively. The electrical and thermal conductivities are significantly reduced compared to Ni and the temperature dependence of lattice thermal conductivity exhibits a glass-like plateau. Inelastic neutron scattering measurements suggest weak anharmonicity so that the thermal transport is expected to be dominated by the defect scattering.

Mode distribution analysis for superionic melt of CuI by coherent quasielastic neutron scattering

Kawakita, Yukinobu; Kikuchi, Tatsuya*; Tahara, Shuta*; Nakamura, Mitsutaka; Inamura, Yasuhiro; Maruyama, Kenji*; Yamauchi, Yasuhiro*; Kawamura, Seiko; Nakajima, Kenji

JPS Conference Proceedings (Internet), 33, p.011071_1 - 011071_6, 2021/03

BB2019-1144.pdf:0.7MB

https://doi.org/10.7566/JPSCP.33.011071

CuI is a well-known superionic conductor in a high temperature solid phase where the mobile cations migrate between interstitial sites in the f.c.c. sublattice formed by iodine ions. Even in the molten state, it shows several features suggesting collective or cooperative ionic motion. MD results show that Cu diffuses much faster than I. The Cu-Cu partial structure factor have a FSDP which indicates a medium-range ordering of Cu ions. Moreover the Cu-Cu partial pair distribution deeply penetrates into the nearest neighboring Cu-I shell. To reveal origin such anomalous behaviors of molten CuI, we performed quaiselastic neutron scattering (QENS) by the disk-chopper spectrometer AMATERAS at MLF, J-PARC. To interpret the total dynamic structure factor obtained from coherent QENS, the mode distribution analysis was applied. It is found that the motion of iodine is a kind of fluctuating within an almost local area while Cu ions diffuse much faster than iodine ions.

Sequence-dependent hydration water dynamics of dodecameric DNA

Nakagawa, Hiroshi; Yonetani, Yoshiteru*; Nakajima, Kenji; Kawamura, Seiko; Kikuchi, Tatsuya*; Inamura, Yasuhiro; Kataoka, Mikio*; Kono, Hidetoshi*

JPS Conference Proceedings (Internet), 33, p.011101_1 - 011101_6, 2021/03

https://doi.org/10.7566/JPSCP.33.011101

Hydration water dynamics were measured by quasi-elastic neutron scattering with HnO/DO contrast for two DNA dodecamers, 5'CGCGCGCG'3 and 5'CGCGCGCG'3, which have been computationally shown to be structurally rigid and flexible, respectively. The dynamical transitions of the hydration water as well as DNA were observed for both sequences at approximately 240 K. Above the transition temperature, the mean square displacements of the hydration water for the rigid sequence were smaller than those for the flexible one. Furthermore, the relaxation time of the hydration water was longer in the rigid DNA than in the flexible DNA. We suggest that hydration water dynamics on the picosecond timescale are associated with sequence-dependent deformability of DNA.

Applicability and limitations of analysis transformed from the inelastic neutron scattering data

Nakamura, Mitsutaka; Kikuchi, Tatsuya*; Kawakita, Yukinobu

Physica B; Condensed Matter, 567, p.61 - 64, 2019/08

BB2018-0571.pdf:1.79MB

https://doi.org/10.1016/j.physb.2019.01.002

Recently, we reported the phonon dynamical study of a polycrystalline NaI by using the dynamical structure factor in real-space transformed from the inelastic neutron scattering (INS) data. Our study has shown that the INS experiments under the conventional condition Q 5 can provide us a meaningful information on the phonon dynamics at around the first nearest neighbor distance on accepting the worse real-space resolution. These results suggest the possibility that a large amount of data which were previously obtained can be effectively reused. In this study, we will examine both the applicability and limitations of analysis for various types of materials whose INS data were obtained at the Fermi chopper spectrometer 4SEASONS in J-PARC.

Background issues encountered by cold-neutron chopper spectrometer AMATERAS

Kikuchi, Tatsuya*; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Nakamura, Mitsutaka; Wakai, Daisuke*; Aoyama, Kazuhiro*; Iwahashi, Takaaki*; Kambara, Wataru*

Physica B; Condensed Matter, 564, p.45 - 53, 2019/07

https://doi.org/10.1016/j.physb.2019.02.015

Details of the background, that is, unwanted signals accumulated by the data acquisition system of neutron instruments, observed by the cold-neutron chopper spectrometer AMATERAS installed at the Materials and Life Science Experimental Facility at J-PARC are reported. In the design phase of AMATERAS, we carefully considered the achievement of high signal-to-noise ratio, and possible countermeasures were implemented. Actually, recent scientific outputs from AMATERAS indicates that the spectrometer is one of excellent neutron instruments with low background. In spite of that, in nine years of AMATERAS operation, we have encountered unwanted signals due to various reasons, including gamma-rays emitted at materials on or near the beam line including the sample itself, scattered neutrons from the beam line devices, air scattering, electronic noise in data acquisition system, cosmic rays, T0 burst, and other unknown sources. In this report, we discuss the background observed by AMATERAS, especially in the conditions of without samples, comprehensively. The possible sources of these signals and the countermeasures considered against the above sources are discussed, which may be helpful to those who are engaged in other existing or planned neutron-scattering instruments.

Colossal barocaloric effects in plastic crystals

Li, B.*; Kawakita, Yukinobu; Kawamura, Seiko; Sugahara, Takeshi*; Wang, H.*; Wang, J.*; Chen, Y.*; Kawaguchi, Saori*; Kawaguchi, Shogo*; Ohara, Koji*; et al.

Nature, 567(7749), p.506 - 510, 2019/03

https://doi.org/10.1038/s41586-019-1042-5

Refrigeration is of vital importance for modern society for example, for food storage and air conditioning- and 25 to 30% of the world's electricity is consumed for refrigeration. Current refrigeration technology mostly involves the conventional vapour compression cycle, but the materials used in this technology are of growing environmental concern because of their large global warming potential. As a promising alternative, refrigeration technologies based on solid-state caloric effects have been attracting attention in recent decades. However, their application is restricted by the limited performance of current caloric materials, owing to small isothermal entropy changes and large driving magnetic fields. Here we report colossal barocaloric effects (CBCEs) (barocaloric effects are cooling effects of pressure-induced phase transitions) in a class of disordered solids called plastic crystals. The obtained entropy changes in a representative plastic crystal, neopentylglycol, are about 389 joules per kilogram per kelvin near room temperature. Pressure-dependent neutron scattering measurements reveal that CBCEs in plastic crystals can be attributed to the combination of extensive molecular orientational disorder, giant compressibility and highly anharmonic lattice dynamics of these materials. Our study establishes the microscopic mechanism of CBCEs in plastic crystals and paves the way to next-generation solid-state refrigeration technologies.

Anomaly of structural relaxation in complex liquid metal of bismuth; Dynamic correlation function of coherent quasi-elastic neutron scattering

Kawakita, Yukinobu; Kikuchi, Tatsuya*; Inamura, Yasuhiro; Tahara, Shuta*; Maruyama, Kenji*; Hanashima, Takayasu*; Nakamura, Mitsutaka; Kiyanagi, Ryoji; Yamauchi, Yasuhiro*; Chiba, Kaori*; et al.

Physica B; Condensed Matter, 551, p.291 - 296, 2018/12

https://doi.org/10.1016/j.physb.2017.12.037

There are elemental liquid metals with complex structures far from the hard sphere (HS) packing model. Liquid Bi has an asymmetric first peak in the structure factors S(Q). The pair distribution function g(r) exhibits strange distance ratio of 1:2 between the first and the second peaks. Since a HS model with two kinds of radius produces asymmetry of the main peak in S(Q), existence of short-lived covalent bonds was discussed. Contrarily, modulation of the atomic distribution by the Friedel oscillations of shielding electrons around metallic ions was discussed. To examine its bonding nature from viewpoints of dynamic correlation functions, we have measured neutron quasielastic scattering of liquid Bi by using cold disk chopper spectrometer installed at MLF of J-PARC. The van Hove function revealed that the shoulder structure located at a longer side of the first peak in g(r) exhibits a longer relaxation time than the main structures such as the first and second peaks.

Detailed study of the structure of the low-energy magnetic excitations in overdoped LaSrCuO

Ikeuchi, Kazuhiko*; Kikuchi, Tatsuya*; Nakajima, Kenji; Kajimoto, Ryoichi; Wakimoto, Shuichi; Fujita, Masaki*

Physica B; Condensed Matter, 536, p.717 - 719, 2018/05

https://doi.org/10.1016/j.physb.2017.11.022

To examine the detailed structure of low-energy magnetic excitations in a high-transition-temperature superconducting cuprate with heavily hole-doping, we performed inelastic neutron scattering experiments on LaSrCuO. We observed clear dispersion relations of the previously reported incommensurate (IC) magnetic correlations at = (0.5 , 0.5)/(0.5, 0.5 ). In addition, we show the emergence of continuum magnetic excitations with a ring shape centered at point in a constant energy spectrum at = 50 K. The radius of the ring ( = 0.109) is smaller than the incommensurability ( = 0.118). This suggests that the origin of the ring-like excitations is different from that of the IC magnetic correlations, and the low-energy magnetic excitations of the LaSrCuO system are inherently composed of these two kinds of excitations.

Retreat from stress; Rattling in a planar coordination

Suekuni, Koichiro*; Lee, C. H.*; Tanaka, Hiromi*; Nishibori, Eiji*; Nakamura, Atsushi*; Kasai, Hidetaka*; Mori, Hitoshi*; Usui, Hidetomo*; Ochi, Masayuki*; Hasegawa, Takumi*; et al.

Advanced Materials, 30(13), p.1706230_1 - 1706230_6, 2018/03

https://doi.org/10.1002/adma.201706230

Thermoelectric materials for highly efficient devices must satisfy conflicting requirements of high electrical conductivity and low thermal conductivity. In this paper, we studied the crystal structure and phonon dynamics of tetrahedrites (Cu,Zn)(Sb,As)S. The results revealed that the Cu atoms in a planar coordination are rattling, which effectively scatter phonons. These findings provide a new strategy for the development of highly efficient thermoelectric materials with planar coordination.