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Journal Articles

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 and Technology, 99, p.55 - 60, 2022/02

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.

Journal Articles

Screw dislocation-spherical void interactions in fcc metals and their dependence on stacking fault energy

Hayakawa, Sho*; Doihara, Kohei*; Okita, Taira*; Itakura, Mitsuhiro; Aichi, Masaatsu*; Suzuki, Katsuyuki*

Journal of Materials Science, 54(17), p.11509 - 11525, 2019/09

 Times Cited Count:6 Percentile:50.98(Materials Science, Multidisciplinary)

Journal Articles

Atomistic simulations for the effects of stacking fault energy on defect formations by displacement cascades in FCC metals under Poisson's deformation

Hayakawa, Sho*; Okita, Taira*; Itakura, Mitsuhiro; Kawabata, Tomoya*; Suzuki, Katsuyuki*

Journal of Materials Science, 54(16), p.11096 - 11110, 2019/08

 Times Cited Count:3 Percentile:28.74(Materials Science, Multidisciplinary)

Journal Articles

Effect of strong gravitational field on oriented crystalline perovskite-type manganese oxide La$$_{1-x}$$Sr$$_x$$MnO$$_3$$

Tokuda, Makoto*; Mashimo, Tsutomu*; Khandaker, J. I.*; Ogata, Yudai; Mine, Yoji*; Hayami, Shinya*; Yoshiasa, Akira*

Journal of Materials Science, 51(17), p.7899 - 7906, 2016/09

 Times Cited Count:2 Percentile:10.2(Materials Science, Multidisciplinary)

Journal Articles

Synthesis of multilayered composite nanotube heterostructure; SiC-SiO$$_{2}$$, C-SiO$$_{2}$$, and C-SiC-SiO$$_{2}$$ nanotubes

Taguchi, Tomitsugu; Shamoto, Shinichi

Journal of Materials Science, 47(10), p.4363 - 4369, 2012/05

 Times Cited Count:3 Percentile:12.91(Materials Science, Multidisciplinary)

Three types of composite nanotube heterostructures (two double-layered and one triple-layered structure) are synthesized by simple heat treatment, forming SiC-SiO$$_{2}$$, C-SiO$$_{2}$$, and C-SiC-SiO$$_{2}$$ composite coaxial nanotubes. These multilayered composite nanotubes consist of several components with different electrical properties, for example, metal, semiconductor and insulator components. In particular, C-SiC-SiO$$_{2}$$ triple-layered nanotubes with metallic, semiconducting and insulating layers are synthesized for the first time. These multilayered nanotubes can be expected to find applications in nanoscale heterostructure electronic and optical devices.

Journal Articles

Synthesis and properties of ceramic fibers from polycarbosilane/polymethylphenylsiloxane polymer blends

Kita, Kenichiro; Narisawa, Masaki*; Nakahira, Atsushi*; Mabuchi, Hiroshi*; Sugimoto, Masaki; Yoshikawa, Masahito

Journal of Materials Science, 45(13), p.3397 - 3404, 2010/04

 Times Cited Count:9 Percentile:32.88(Materials Science, Multidisciplinary)

We synthesized ceramic fibers based on silicon carbide (SiC) from polymer blends of polycarbosilane (PCS) and polymethylphenylsiloxane (PMPhS). PMPhS was compatible with PCS up to 30 mass%. The polymer blend was formed a transparent melt at temperatures higher than 513 K and the softening point was also lowered by adding PMPhS. 15 mass% of PMPhS to PCS was the most suitable condition for obtaining thin fibers with an average diameter of 14.4 $$mu$$m and the ceramic yield of the cured fiber was 85.5% after pyrolysis at 1273 K. In spite of the small diameter, the resulting tensile strength at 1273 K was rather limited at 0.78 GPa. After high temperature pyrolysis at 1673$$sim$$1773 K, a porous nanocrystalline SiC fiber with a unique microstructure was obtained with surface area of 70$$sim$$150 m$$^{2}$$/g.

Journal Articles

High-temperature pyrolysis of ceramic fibers derived from polycarbosilane-polymethylhydrosiloxane polymer blends with porous structures

Kita, Kenichiro; Narisawa, Masaki*; Nakahira, Atsushi*; Mabuchi, Hiroshi*; Ito, Masayoshi*; Sugimoto, Masaki; Yoshikawa, Masahito

Journal of Materials Science, 45(1), p.139 - 145, 2010/01

 Times Cited Count:8 Percentile:30.01(Materials Science, Multidisciplinary)

The polymer blends of polycarbosilane (PCS) and polymethylohydrosiloxane with high molecular weight (PMHS-h) were prepared by freeze-drying process. Melt viscosity, themogravimetric analysis, and gas evolution from the polymer blends were analyzed. The polymer blend of HSah15 (15 mass% PMHS-h to PCS) was melt-spun to fiber form, curing by thermal oxidation and pyrolyzed at various temperatures up to 1773 K. The fibers were investigated by tensile tests, FE-SEM observation, and XRD (X-ray diffraction) analysis. After pyrolysis at 1273 K, there were amounts of pores in the cross sections of the fiber derived from HSah15, and after pyrolysis at 1773 K, no remarkable $$beta$$-SiC crystal were formed on the outside surface of the fiber derived from HSah15.

Journal Articles

Long-term performance of polyetheretherketone-based polymer electrolyte membrane in fuel cells at 95$$^{circ}$$C

Chen, J.; Zhai, M.*; Asano, Masaharu; Huang, L.*; Maekawa, Yasunari

Journal of Materials Science, 44(14), p.3674 - 3681, 2009/07

 Times Cited Count:25 Percentile:62.97(Materials Science, Multidisciplinary)

A poly(styrenesulfonic acid)-grafted polyetheretherketone (ssPEEK) polymer electrolyte membrane was developed by radiation grafting of ethyl styrenesulfonate (ETSS) onto PEEK film and subsequent hydrolysis. The long-term durability of the ssPEEK membrane was tested in a fuel cell, and it exhibited a lifetime of more than 1,000 h and a slow voltage degradation. After durability test, the catalyst layers were analyzed by XRD and TEM; the membrane was investigated by determining the change in thickness, proton conductivity and amounts of sulfonic acid groups. It was concluded that the degradation of performance in fuel cell was due to the thermal aging of the hydrocarbon membrane exposed to the electrochemical environment using the pure oxygen as the oxidant gas, as well as the Nafion-based catalyst layer being subject to high temperature for a long time, where the Pt catalyst was aggregated and sintered.

Journal Articles

Carcinogen adsorbent prepared from DNA complex by $$gamma$$-ray irradiation

Furusawa, Kazuya*; Kita, Erika*; Saeki, Toshihiko*; Nagasawa, Naotsugu; Nishi, Norio*; Dobashi, Toshiaki*

Journal of Biomaterials Science; Polymer Edition, 19(9), p.1159 - 1170, 2008/09

To insolubilize DNA for preparing a novel carcinogen adsorbent, effects of $$gamma$$-ray irradiation on aqueous solutions of mixtures of DNA with cross-linking biopolymers (CBP): gelatin, bovine serum albumin, carboxymethyl cellulose and hydroxyethyl-cellulose, O-[2-hydroxy-3-(trimethyl ammonio)-propyl], chloride have been studied. DNA-CBP hybrid gels were successfully prepared from aqueous mixtures of DNA with CBP in a limited range of irradiation dose. Gel fraction (Gf) and swelling ratio (S) of the hybrid gels were measured. The Gf and S of hybrid gels increased and decreased, respectively, with increasing irradiated dose. Adsorption of one of carcinogen, acridine orange, was also examined for the gels. From the experimental results, the optimum condition for preparing insolubilized homogeneous DNA gels was determined.

Journal Articles

Influence of pre-irradiation atmosphere on the properties of polymer electrolyte membranes prepared using radiation grafting method

Septiani, U.*; Chen, J.; Asano, Masaharu; Maekawa, Yasunari; Yoshida, Masaru; Kubota, Hitoshi*

Journal of Materials Science, 42(4), p.1330 - 1335, 2007/02

 Times Cited Count:15 Percentile:48.28(Materials Science, Multidisciplinary)

The influence of pre-irradiation atmosphere, argon and air, on radiation grafting of styrene into poly(ethylene-co-tetrafluoroethylene) (ETFE) films and the properties of the ETFE-based radiation-grafted polymer electrolyte membranes were investigated. The preparation and properties of the membranes were found to be strongly influenced by the $$gamma$$-ray pre-irradiation atmosphere. The proton conductivity was measured in its water-saturated state at 25$$^{circ}$$C, and the membrane durability was tested in a 3 % H$$_{2}$$O$$_{2}$$ aqueous solution at 60$$^{circ}$$C. The proton conductivity of the membrane prepared by pre-irradiation under air was higher than that of the membrane prepared under argon with the same ion exchange capacity level. However, the durability of the former was considerably lower than that of the latter. For instance, the membrane with an ion exchange capacity of about 1.0 mmolg-1 prepared under argon was twice as durable as that prepared under air. It was considered that the lower durability of the membrane prepared by pre-irradiation under air was because of the unstable ether bond introduced between the graft chains and the backbone chains. : polymer electrolyte membrane (PEM); radiation grafting; styrene; durability; ETFE

Journal Articles

Synthesis of a minute SiC product from polyvinylsilane with radiation curing, 2; Ceramization process of radiation cured polyvinylsilane

Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito; Tanaka, Shigeru; Narisawa, Masaki*; Okamura, Kiyohito*; Ito, Masayoshi*

Journal of Materials Science, 42(1), p.130 - 135, 2007/01

 Times Cited Count:2 Percentile:10.8(Materials Science, Multidisciplinary)

We have synthesized minute SiC products from polyvinylsilane (PVS), which is a liquid organosilicon polymer, with radiation curing. Since there is a close relationship between the properties of obtained SiC products and pyrolysis condition, it is important to investigate the ceramization process of PVS in order to find out the optimum pyrolysis condition. In this paper, the ceramization process of the PVS cured by $$gamma$$-ray irradiation at room temperature was investigated by gas analysis, thermogravimetric analysis, density measurement, and so on. It was found that the ceramization of $$gamma$$-ray cured PVS starts above 500K, and that drastic organic-inorganic conversion occurs in the temperature range of 700-1100K. According to the results of the changes of mass and density, it was found that the volume shrinkage of PVS during the curing and pyrolysis processes is 80%. The SiC obtained by pyrolysis at 1573K showed the density of 2.50g/cm$$^{3}$$ and microvickers hardness of 31.6GPa.

Journal Articles

Improvement of chemical stability of polymer electrolyte fuel cell membranes by grafting of new substituted styrene monomers into ETFE films

Chen, J.; Asano, Masaharu; Yamaki, Tetsuya; Yoshida, Masaru

Journal of Materials Science, 41(4), p.1289 - 1292, 2006/02

 Times Cited Count:19 Percentile:56.71(Materials Science, Multidisciplinary)

The MeSt/tBuSt/DVB-grafted polymer electrolyte membrane showed a high performance for the fuel cell applications. The tBuSt contributed the high chemical stability while the MeSt contributed the high conductivity to the resulted membrane. The DVB crosslinker in the membrane further improved the chemical stability. The new polymer electrolyte membrane with a degree of grafting of 36% showed proton conductivity as high as the Gore-Select membrane, and the durability time was about 3 times longer than that of the traditional styrene/DVB-grafted one. Therefore, the MeSt/tBuSt/DVB-grafted polymer electrolyte membrane was more possible to be used for the fuel cells.

Journal Articles

Synthesis of a minute SiC product from polyvinylsilane with radiation curing, 1; Radiation curing of polyvinylsilane

Idesaki, Akira; Sugimoto, Masaki; Tanaka, Shigeru; Narisawa, Masaki*; Okamura, Kiyohito*; Ito, Masayoshi*

Journal of Materials Science, 39(18), p.5689 - 5694, 2004/09

 Times Cited Count:6 Percentile:29.02(Materials Science, Multidisciplinary)

Irradiation effect of $$gamma$$-ray on polyvinylsilane (PVS), which is a liquid organosilicon polymer, was investigated and the optimum curing condition to synthesize a minute SiC product with radiation curing was discussed. Room temperature and liquid nitrogen temperature (77K) were examined as the irradiation temperature. In both cases, the cured PVS maintaining its formed shape could be obtained by $$gamma$$-ray irradiation under vacuum, and the cured PVS in solid state at room temperature was obtained by irradiation with dose of above 3-4MGy. It was found that the efficiency of crosslinking in case of the irradiation at room temperature is higher than that in case of irradiation at 77K. The PVS injected into a mold was irradiated by $$gamma$$-ray with dose of 3.6MGy at room temperature under vacuum, and pyrolyzed at 1273 K in Ar gas atmosphere. As a result, minute SiC products which had similar shapes to the mold and the sizes of 30-60$$mu$$m were obtained.

Journal Articles

Interfacial properties of a direct bonded Nd-doped YVO$$_{4}$$ and YVO$$_{4}$$ single crystal

Sugiyama, Akira; Nara, Yasunaga; Wada, Kengo*; Fukuyama, Hiroyasu

Journal of Materials Science; Materials in Electronics, 15(9), p.607 - 612, 2004/09

Laser crystal bonding of a neodymium-doped yttrium orthovanadate (Nd: YVO$$_{4}$$) and a non-doped yttrium orthovanadate (YVO$$_{4}$$) crystal as a cold finger has been demonstrated. Instead of a traditional chemical treatment, a newly developed dry etching process was applied to the preparation for contact of mechanically polished surfaces. In the subsequent heat treatment process, stable heating at 873 K was required to prevent precipitation at the bonded interface. The bonded interface of 3 mm $$times$$ 3 mm was investigated by optical scattering and wavefront distortion measurements. The scattering density around the bonded interface was less than 4.6$$times$$10$$^{6}$$ /cm$$^{3}$$ and the wavefront distortion caused by the bonded region was assumed to be around 0.04-wave at 633 nm. Additional magnified inspection showed that atoms in the bonded region were well arranged with the same regularity as the bulk crystal. The diffusion coefficient of Nd$$^{3+}$$ ions in the YVO$$_{4}$$ crystal was estimated at 2.3$$times$$10$$^{-23}$$ m$$^{2}$$/sec at 873 K.

Journal Articles

The Toughness of free-standing CVD diamond

Davies, A. R.*; Field, J. E.*; Takahashi, Koji; Hada, Kazuhiko

Journal of Materials Science, 39(5), p.1571 - 1574, 2004/03

 Times Cited Count:6 Percentile:29.02(Materials Science, Multidisciplinary)

A four-point bend test was used to determine the fracture toughness of mechanical grade and di-electric (optical) grade chemical vapour deposited (CVD) diamond. The validity of the test was first confirmed by measuring the toughness of alumina and confirming the results with literature values. The toughnesses of both types of CVD were similar; 8.5$$pm$$1.0 and 8.3$$pm$$0.4 MPa ($$sqrt{m}$$) respectively. This is higher than the value of 3.4$$pm$$0.5 MPa ($$sqrt{m}$$) measured for diamond by Field and Freeman, 1981 using an indentation technique. It is suggested that this is primarily due to differences in surface roughness. There were enough samples to make a preliminary study of the effect of temperature and these data are reported.

Journal Articles

Fabrication and characterization of C-doped anatase TiO$$_{2}$$ photocatalysts

Choi, Y.; Umebayashi, Tsutomu; Yoshikawa, Masahito

Journal of Materials Science, 39(5), p.1837 - 1839, 2004/03

 Times Cited Count:215 Percentile:98.07(Materials Science, Multidisciplinary)

Carbon (C)-doped anatase TiO$$_{2}$$ photocatalysts have been prepared by the oxidative annealing of TiC powders at 623 K for 50-100 hrs. From XRD and XPS analysis, it is clear that C is incorporated into O site of the TiO$$_{2}$$ lattice. Diffuse reflectance spectroscopy (DRS) showed that the optical absorption edge of the C-doped anatase TiO$$_{2}$$ shifted to lower energy compared with that of pure anatase TiO$$_{2}$$. The decomposition of methylene blue (MB) adsorbed on the C-doped sample was observed under a visible light range of 420-500 nm. We conclude that substitution of C for O in the TiO$$_{2}$$ leads to a photocatalytic decomposition of MB under visible light irradiation.

Journal Articles

Fabrication of TiO$$_{2}$$ photocatalysts by oxidative annealing of TiC

Choi, Y.; Umebayashi, Tsutomu; Yamamoto, Shunya; Tanaka, Shigeru

Journal of Materials Science Letters, 22(17), p.1209 - 1211, 2003/09

 Times Cited Count:45 Percentile:79.28(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Improved cooling performance of ytterbium-doped glass combined with sapphire

Nishimura, Akihiko; Sugiyama, Akira; Usami, Tsutomu; Ohara, K.*

Journal of Materials Science; Materials in Electronics, 14(1), p.1 - 3, 2003/01

no abstracts in English

Journal Articles

High-quality epitaxial TiO$$_{2}$$ thin films grown on $$alpha$$-Al$$_{2}$$O$$_{3}$$ substrates by pulsed laser deposition

Shinohara, Ryuji*; Yamaki, Tetsuya; Yamamoto, Shunya; Ito, Hisayoshi; Asai, Keisuke*

Journal of Materials Science Letters, 21(12), p.967 - 969, 2002/06

 Times Cited Count:9 Percentile:38.24(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Fine SiC fiber synthesized from organosilicon polymers; Relationship between spinning temperature and melt viscosity of precursor polymers

Idesaki, Akira; Narisawa, Masaki*; Okamura, Kiyohito*; Sugimoto, Masaki; Tanaka, Shigeru; Morita, Yosuke; Seguchi, Tadao; Ito, Masayoshi*

Journal of Materials Science, 36(23), p.5565 - 5569, 2001/12

 Times Cited Count:36 Percentile:77.69(Materials Science, Multidisciplinary)

A very fine silicon carbide (SiC) fiber with diameter of 6 $$mu$$ m, about a half of that of a commercially available SiC fiber, was synthesized from a polymer blend of polycarbosilane (PCS) and polyvinylsilane (PVS). The fine SiC fiber was obtained by optimizing the composition and the spinning temperature of PCS-PVS polymer blends. In order to determine these optimum conditions, the relationship between temperature and melt viscosities of the polymer blends was investigated. As a result, it was found that the optimum spinning temperature range was within a temperature range where the melt viscosity is 5-10Pa$$cdot$$s. Moreover, by blending PVS with PCS, the spinning temperature of the polymer blends was lowered, the spinnability of polymer system was improved, and finer polymer fiber was obtained compared with PCS. The optimum content of PVS in the polymer blend was 15-20wt%.

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