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Journal Articles

Local structure analysis of KNbO$$_3$$ nanocubes by solvothermal synthesis

Yoneda, Yasuhiro; Kohara, Shinji*; Nakashima, Koichi*; Nagata, Hajime*; Wada, Satoshi*

Japanese Journal of Applied Physics, 54(10S), p.10NC01_1 - 10NC01_6, 2015/10

 Times Cited Count:4 Percentile:19.7(Physics, Applied)

The atomic-scale structure of KNbO$$_3$$ nanopowder synthesized by solvothermal method has been studied using high-energy X-ray diffraction, Rietveld refinement, and the atomic pair-distribution function (PDF) technique. It was found that the local structure of KNbO$$_3$$ nanoparticles deviates from the average structure. The local structure was found to be rhombohedral structure though the average structure was tetragonal structure. The rhombohedral distortion of NbO$$_6$$ octahedra was maintained in the annealed sample.

Journal Articles

Progress of divertor simulation research toward the realization of detached plasma using a large tandem mirror device

Nakashima, Yosuke*; Takeda, Hisahito*; Ichimura, Kazuya*; Hosoi, Katsuhiro*; Oki, Kensuke*; Sakamoto, Mizuki*; Hirata, Mafumi*; Ichimura, Makoto*; Ikezoe, Ryuya*; Imai, Tsuyoshi*; et al.

Journal of Nuclear Materials, 463, p.537 - 540, 2015/08

 Times Cited Count:18 Percentile:84.56(Materials Science, Multidisciplinary)

Journal Articles

Local structure analysis of Nb-related perovskite materials

Yoneda, Yasuhiro; Kohara, Shinji*; Nagata, Hajime*; Fu, D.*; Takenaka, Tadashi*

Transactions of the Materials Research Society of Japan, 39(4), p.455 - 458, 2014/12

NaNbO$$_3$$, KNbO$$_3$$, and AgNbO$$_3$$ have rhombohedral structure at low temperatures. The phase transition depends on ${it A}$-site ion with NbO$$_6$$ octahedron. NaNbO$$_3$$ and KNbO$$_3$$ have structural phase transition from rhombohedral to orthorhombic with increasing temperature. On the other hand, the phase transition of AgNbO$$_3$$ occurs from rhombohedral to monoclinic. Since the rhombohedral structure is a highly ordered average structure, it tends to be subject to the influence of local randomness. We performed local structure analysis by using atomic pair-distribution function (PDF). The Nb-O bond clearly appeared in the observed distribution for NaNbO$$_3$$, but degraded in that for AgNbO$$_3$$. The difference of local structures causes different successive phase transitions for the Nb-related perovskite materials.

Journal Articles

Development of divertor simulation research in the GAMMA 10/PDX tandem mirror

Nakashima, Yosuke*; Sakamoto, Mizuki*; Yoshikawa, Masayuki*; Oki, Kensuke*; Takeda, Hisahito*; Ichimura, Kazuya*; Hosoi, Katsuhiro*; Hirata, Mafumi*; Ichimura, Makoto*; Ikezoe, Ryuya*; et al.

Proceedings of 25th IAEA Fusion Energy Conference (FEC 2014) (CD-ROM), 8 Pages, 2014/10

Journal Articles

Ion irradiation effects on the optical properties of tungsten oxide films

Nagata, Shinji*; Fujita, Haruka*; Inoue, Aichi; Yamamoto, Shunya; Tsuchiya, Bun*; Shikama, Tatsuo*

Nuclear Instruments and Methods in Physics Research B, 268(19), p.3151 - 3154, 2010/10

 Times Cited Count:3 Percentile:29.26(Instruments & Instrumentation)

A tungsten tri-oxide (WO$$_{3}$$) film covered with a thin catalyst layer is one of the candidates for hydrogen sensing devices that show a reversible coloration under hydrogen exposure. While the injection of the cations and/or the formation of the oxygen vacancies can be responsible for the coloration of the film, the mechanism of the gasochromic phenomenon is not fully understood. In the present work, the changes of the optical properties in the WO$$_{3}$$ film by ion irradiation were investigated to clarify the relation between the coloration and oxygen vacancies. WO$$_{3}$$ films of 300-500 nm thicknesses were deposited on SiO$$_{2}$$ substrates by magnetron sputtering. Oxygen ions at energies between 200 and 800 keV were irradiated to the WO$$_{3}$$ films. The optical absorption of the film was measured in the wavelengths between 190 and 1000 nm. The results show that the change of optical-absorption coefficient in WO$$_{3}$$ films depends on both electronic and nuclear stopping powers.

Journal Articles

Application of X-ray photoelectron spectroscopy to characterization of Au nanoparticles formed by ion implantation into SiO$$_{2}$$

Takahiro, Katsumi*; Oizumi, Shinnosuke*; Morimoto, Keiichi*; Kawatsura, Kiyoshi*; Isshiki, Toshiyuki*; Nishio, Koji*; Nagata, Shinji*; Yamamoto, Shunya; Narumi, Kazumasa; Naramoto, Hiroshi*

Applied Surface Science, 256(4), p.1061 - 1064, 2009/11

 Times Cited Count:8 Percentile:37.34(Chemistry, Physical)

Journal Articles

Ion-induced self-organized ripple patterns on graphite and diamond surfaces

Takahiro, Katsumi*; Ozaki, Koichi*; Kawatsura, Kiyoshi*; Nagata, Shinji*; Yamamoto, Shunya; Narumi, Kazumasa; Naramoto, Hiroshi*

Applied Surface Science, 256(4), p.972 - 975, 2009/11

 Times Cited Count:12 Percentile:48.7(Chemistry, Physical)

Journal Articles

Effect of 14-MeV neutrons on strontium-aluminate-based long-lasting phosphor

To, Kentaro; Shikama, Tatsuo*; Katsui, Hirokazu*; Nagata, Shinji*; Tsuchiya, Bun*; Yamauchi, Michinori*; Nishitani, Takeo

Journal of Nuclear Materials, 386-388, p.1027 - 1029, 2009/04

 Times Cited Count:4 Percentile:31.45(Materials Science, Multidisciplinary)

Fluorescence and long-lasting emission properties of two types of Long-lasting phosphors (LLPs), SrAl$$_{2}$$O$$_{4}$$:Eu$$^{2+}$$,Dy$$^{3+}$$ and Sr$$_{4}$$Al$$_{14}$$O$$_{25}$$:Eu$$^{2+}$$,Dy$$^{3+}$$, were examined under 14-MeV neutron irradiation. The fluorescent spectra of the LLPs have characteristic peaks due to their dopants and the fluorescent intensity of Sr$$_{4}$$Al$$_{14}$$O$$_{25}$$:Eu$$^{2+}$$,Dy$$^{3+}$$ shows good radiation resistance for the neutrons fluence up to 10$$^{19}$$ n/m$$^{2}$$. Long-lasting emissions are exhibited after neutron irradiation, and the emission spectra have one peak due to Eu$$^{2+}$$. Further, it is found that there is an optimum neutron fluence at which the longest decay time is obtained.

Journal Articles

Damage process and luminescent characteristics in silica glasses under ion irradiation

Nagata, Shinji*; Katsui, Hirokazu*; Tsuchiya, Bun*; Inoue, Aichi; Yamamoto, Shunya; To, Kentaro; Shikama, Tatsuo*

Journal of Nuclear Materials, 386-388, p.1045 - 1048, 2009/04

 Times Cited Count:13 Percentile:65.91(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Hydrogen retention induced by ion implantation in tungsten trioxide films

Inoue, Aichi; Yamamoto, Shunya; Nagata, Shinji*; Yoshikawa, Masahito; Shikama, Tatsuo*

Nuclear Instruments and Methods in Physics Research B, 267(8-9), p.1480 - 1483, 2009/03

 Times Cited Count:12 Percentile:63.47(Instruments & Instrumentation)

We quantitatively studied the relation between hydrogen retention and optical properties induced by hydrogen ion implantation in tungsten trioxide (WO$$_{3}$$) films. Films of WO$$_{3}$$ (300 nm) covered with tungsten metal layers (200 nm) were prepared on transparent SiO$$_{2}$$ substrates by a reactive sputtering in Ar and O$$_{2}$$ mixture. When H$$_{2}$$$$^{+}$$ ions were implanted into the samples at an acceleration voltage of 10 kV, the concentration of hydrogen retaining in the WO$$_{3}$$ films increased up to 0.4 H/W in proportion to the fluence of H$$_{2}$$$$^{+}$$ ions. The optical absorption coefficient at 750 nm of samples increased linearly by 3 $$mu$$m$$^{-1}$$ with increasing the concentration of hydrogen implanted up to 0.1 H/W. And then, increased and saturated at 4 $$mu$$m$$^{-1}$$ with the increase of hydrogen concentration higher than 0.1 H/W. It was found that the hydrogen retention up to 0.1 H/W in tungsten trioxide layers can be monitored by measuring the optical absorbance.

Journal Articles

Ion induced structural modification and nano-crystalline formation of Zr-Al-Ni-Cu metallic glasses

Nagata, Shinji*; Sasase, Masato*; Takahiro, Katsumi*; Tsuchiya, Bun*; Inoue, Aichi; Yamamoto, Shunya; Shikama, Tatsuo*

Nuclear Instruments and Methods in Physics Research B, 267(8-9), p.1514 - 1517, 2009/03

 Times Cited Count:9 Percentile:54.57(Instruments & Instrumentation)

In this study, effects of the ion implantation on the phase transformation and nano-crystalline formation were examined in Zr-based metallic glasses. Samples were 2 mm thick plates and thin films of Zr$$_{55}$$Al$$_{10}$$Ni$$_{5}$$Cu$$_{30}$$ prepared by casting in a copper mold and by using RF magnetron sputtering, respectively. Ions of Mg, P, Au and Bi with 100-500 keV were implanted in the samples up to 2 $$times$$ 10$$^{16}$$ ions/cm$$^{2}$$ at room temperature. Nano-crystalline structure was found in implanted samples by TEM observation, while the long-range order in the structure was not found for the X-ray diffraction patterns. The electron diffraction patterns indicated the formation of fcc-Zr$$_{2}$$Cu in the P, Au, and Bi implanted region. Changes of the binding energy of the core level electron and valence band structure suggested the formation of Au-Zr or Au-Cu alloys in the Au ion implanted region.

Journal Articles

Status of development of functional materials with perspective on beyond-ITER

Shikama, Tatsuo*; Knitter, R.*; Konys, J.*; Muroga, Takeo*; Tsuchiya, Kunihiko; M$"o$slang, A.*; Kawamura, Hiroshi; Nagata, Shinji*

Fusion Engineering and Design, 83(7-9), p.976 - 982, 2008/12

 Times Cited Count:37 Percentile:90.79(Nuclear Science & Technology)

Functional materials should play an important role not only in ITER but also in fusion machines beyond ITER, though it is occasionally claimed that future fusion plants should have much more simple structures and they should be free from auxiliary systems such as diagnostics. Studies on test blanket modules (TBM) clearly show the importance of functional materials there. The paper will review the present status of studies and developments of functional ceramics for nuclear fusion applications, with a perspective on their application in electric-power generating fusion power plant, namely DEMO.

Journal Articles

Effects of catalyst on gasochromic properties in tungsten oxide films

Inoue, Aichi; Yamamoto, Shunya; Nagata, Shinji*; Yoshikawa, Masahito; Shikama, Tatsuo*

Transactions of the Materials Research Society of Japan, 33(4), p.1127 - 1130, 2008/12

We investigated effects of catalyst on gasochromic properties in tungsten oxide films. Amorphous WO$$_{3}$$ films coated with Pd and Pt catalysts were prepared on SiO$$_{2}$$ substrates by employing reactive RF magnetron sputtering. The field emission scanning electron microscope (FE-SEM) showed that particles with a dozes nm diameter of Pd and with a few nm of Pt grew on the surface at beginning of deposition. The continuous catalytic layers were observed with increasing the amounts of more than 2 nm for Pd and 0.2 nm for Pt catalysts, respectively. When the continuous layers formed on WO$$_{3}$$ surface, the excellent gasochromic properties were obtained. The results indicated that Pt catalysts were suitable for high sensitive hydrogen sensors consisting of gasochromic WO$$_{3}$$ films.

Journal Articles

Effects of composition and structure on hydrogen incorporation in tungsten oxide films deposited by sputtering

Inoue, Aichi; Yamamoto, Shunya; Nagata, Shinji*; Yoshikawa, Masahito; Shikama, Tatsuo*

Nuclear Instruments and Methods in Physics Research B, 266(15), p.3381 - 3386, 2008/08

 Times Cited Count:5 Percentile:39.1(Instruments & Instrumentation)

The effects of composition and structure on hydrogen incorporation property in tungsten oxide films were investigated. The tungsten oxide was deposited on carbon and SiO$$_{2}$$ substrates to form films by varying the temperature from 30 to 600 $$^{circ}$$C using a reactive sputtering in argon and oxygen mixture. We obtained amorphous structure in the films deposited below 400 $$^{circ}$$C and (0 1 0) oriented monoclinic WO$$_{3}$$ in the films deposited beyond 400 $$^{circ}$$C. Hydrogen concentration in the films increased from 0.1 to 0.7 H/W with changing the composition from WO$$_{0.25}$$ to WO$$_{3}$$. The hydrogen concentration in WO$$_{3}$$ films decreased to 0.4 H/W with increasing the substrate temperature during deposition. The Raman spectra of the WO$$_{3}$$ films revealed that decreasing of W$$^{6+}$$=O terminals was related to that of the hydrogen concentration. It was considered in detail that the incorporated hydrogen in tungsten oxide films was bonded at the end of W$$^{6+}$$=O terminals.

Journal Articles

Isotope effects in thermal neutron transmission and backscattering processes for $$varepsilon$$-phase zirconium hydrides and deuterides

Tsuchiya, Bun*; Yasuda, Ryo; Teshigawara, Makoto; Konashi, Kenji*; Nagata, Shinji*; Shikama, Tatsuo*; Yamawaki, Michio*

Journal of Nuclear Materials, 376(1), p.60 - 65, 2008/05

 Times Cited Count:2 Percentile:17.52(Materials Science, Multidisciplinary)

Distributions of hydrogen isotope concentrations in e-phase zirconium hydrides and deuterides ($$varepsilon$$-ZrHx and $$varepsilon$$-ZrDx: 1.8 $$<$$ x $$<$$ 2.0) were investigated by neutron radiography (NRG). The NRG images of the thermal neutron transmission and backscattering revealed hydrogen concentration dependence and isotope differences. The thermal neutron mass attenuation coefficients in relation to the hydrogen isotope concentrations were determined from the transmission NRG images. The results showed the isotope effects of the thermal neutron mass attenuation coefficients for $$varepsilon$$-ZrHx to be about 6-9 times higher than those for $$varepsilon$$-ZrDx. The neutron scattering processes for transmission and backscattering NRG images of $$varepsilon$$-ZrHx and $$varepsilon$$-ZrDx were also analyzed using a general Monte Carlo neutron-particle transport (MCNP) code.

Journal Articles

Hydrogen behavior in gasochromic tungsten oxide films investigated by elastic recoil detection analysis

Inoue, Aichi; Yamamoto, Shunya; Nagata, Shinji*; Yoshikawa, Masahito; Shikama, Tatsuo*

Nuclear Instruments and Methods in Physics Research B, 266(2), p.301 - 307, 2008/01

 Times Cited Count:13 Percentile:65.61(Instruments & Instrumentation)

Changes in the composition and crystalline structure of gasochromic tungsten oxide films resulting from the incorporation of hydrogen were investigated. An uniaxial oriented films in the (0 1 0) plane of monoclinic WO$$_{3}$$ were obtained by reactive RF magnetron sputtering at 600 $$^{circ}$$C. The elastic recoil detection analysis for the films on glassy carbon revealed that the hydrogen impurity was uniformly distributed up to a concentration of 0.24 H/W. The Pd-coated films on SiO$$_{2}$$ turned to blue when they were exposed to a mixture of Ar and 5% H$$_{2}$$ gases. When the sample became colored, the hydrogen concentration in the film increased to 0.47 H/W and the crystalline structure of the film changed from monoclinic to tetragonal. These results indicated that the gasochromic coloration of the tungsten oxide films was accompanied by formation of hydrogen compounds called tungsten bronze (H$$_{x}$$ WO$$_{3}$$).

Journal Articles

Hydrogen incorporation and gasochromic coloration of tungsten oxide films

Nagata, Shinji*; Inoue, Aichi; Yamamoto, Shunya; Tsuchiya, Bun*; Takano, Katsuyoshi; To, Kentaro*; Shikama, Tatsuo*

Journal of Alloys and Compounds, 446-447, p.558 - 561, 2007/10

 Times Cited Count:20 Percentile:70.46(Chemistry, Physical)

The effect of the composition of non-stoichiometric WO$$_{3}$$ films on the gasochromic coloration are investigated. The films are prepared by a reactive RF magnetron sputtering with varying oxygen partial pressure. To determine the quantitative composition of deposited films, Rutherford backscattering spectroscopy (RBS) and Elastic recoil detection (ERD) are employed. Gasochromic coloration of the films coated with Pd catalyst is examined by optical transmission in hydrogen gas. O/W atomic ratio of the films increases from 0.25 to 3.0 with increasing the oxygen partial pressure in the sputtering gas. H/W ratio increases up to 0.7 with increasing the O/W ration. As regards gasochromic coloration, the film with O/W atomic ratio of 3.0 shows superior coloration performance comparing with that of less than 3.0. Therefore, it is assumed that the good gasochromic coloration of tungsten oxide films is realized by near-stoichiometric WO$$_{3}$$. In addition, gasochromic coloration state, increasing of hydrogen concentration in WO$$_{3}$$ films is observed. It indicates that gasochromic coloration of WO$$_{3}$$ is relate to formation of HWO$$_{3}$$ structure.

Journal Articles

Gasochromic properties of nanostructured tungsten oxide films prepared by sputtering deposition

Takano, Katsuyoshi; Inoue, Aichi; Yamamoto, Shunya; Sugimoto, Masaki; Yoshikawa, Masahito; Nagata, Shinji*

Japanese Journal of Applied Physics, Part 1, 46(9B), p.6315 - 6318, 2007/09

 Times Cited Count:9 Percentile:36.92(Physics, Applied)

The amorphous, polycrystalline, and oriented films of the tungsten oxide were fabricated by sputtering deposition. It is found that each film has different roughness in the surface. The films with rough surface show fast coloration in 1% hydrogen. There is possibility that the gasochromic properties are improved effectively by the control of the surface morphology, and the films with large grains on the surface have better gasochromic coloration.

Journal Articles

Search for luminescent materials under 14 MeV neutron irradiation

To, Kentaro*; Shikama, Tatsuo*; Nagata, Shinji*; Tsuchiya, Bun*; Yamauchi, Michinori; Nishitani, Takeo

Journal of Nuclear Materials, 367-370(2), p.1128 - 1132, 2007/08

 Times Cited Count:6 Percentile:43.19(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Luminescence characteristics and defect formation in silica glasses under H and He ion irradiation

Nagata, Shinji*; Yamamoto, Shunya; Inoue, Aichi*; Tsuchiya, Bun*; To, Kentaro*; Shikama, Tatsuo*

Journal of Nuclear Materials, 367-370(2), p.1009 - 1013, 2007/08

 Times Cited Count:29 Percentile:87.26(Materials Science, Multidisciplinary)

no abstracts in English

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