Elastic and dynamical structural properties of La and Mn-doped SrTiO studied by neutron scattering and their relation with thermal conductivities

Kajimoto, Ryoichi; Nakamura, Mitsutaka; Murai, Naoki; Shamoto, Shinichi; Honda, Takashi*; Ikeda, Kazutaka*; Otomo, Toshiya*; Hata, Hiroto*; Eto, Takahiro*; Noda, Masaaki*; et al.

Scientific Reports (Internet), 8(1), p.9651_1 - 9651_8, 2018/06

https://doi.org/10.1038/s41598-018-27984-z

Local structural analysis by using atomic pair distribution function on mixed valence compound LiMnO

Kodama, Katsuaki; Igawa, Naoki; Shamoto, Shinichi; Ikeda, Kazutaka*; Oshita, Hidetoshi*; Kaneko, Naokatsu*; Otomo, Toshiya*; Suzuya, Kentaro; Hoshikawa, Akinori*; Ishigaki, Toru*

JPS Conference Proceedings (Internet), 3, p.013012_1 - 013012_6, 2014/06

https://doi.org/10.7566/JPSCP.3.013012

Inspection and repair techniques in the reactor vessel of the experimental fast reactor Joyo; Development of a high radiation resistance fiberscope (Joint research)

Naito, Hiroyuki; Itagaki, Wataru; Okazaki, Yoshihiro; Imaizumi, Kazuyuki; Ito, Chikara; Nagai, Akinori; Kitamura, Ryoichi; Shamoto, Naoki*; Takeshima, Yoshiyuki*

JAEA-Technology 2012-009, 100 Pages, 2012/05

JAEA-Technology-2012-009.pdf:9.89MB

The radiation characteristics of image fiber and light guide fiber were evaluated to develop a high radiation resistant fiberscope for the fast reactor in-vessel observation. It is known that a pure silica core fiber has a high radiation resistance and radiation resistance is influenced with impurities in silica. Moreover it is necessary to change the clad material of the light guide fiber because that of the current light guide fiber is acrylate, which is weak against radiation. Hence the improved fibers consist of a pure silica core with 1,000 ppm OH and fluorine-doped silica clad. As a result of a irradiation test, we confirm that OH inhibits the generation of the precursor by irradiation. About the clad material, we confirmed that the transmission loss of the fluorine-doped silica clad fiber is smaller than that of the acrylate clad fiber. About the mechanical strength of a fiber, we confirmed that there is no weakening the strength of the fiber and no exfoliation of the coating from the glass. In this study, we discovered the fiber which consists of a pure silica core with 1,000 ppm OH and fluorine-doped silica clad has a high radiation resistance and it is possible to observe using this fiber under the 200 C after 510 Gy irradiation.

Hydrogen in layered iron arsenides; Indirect electron doping to induce superconductivity

Hanna, Taku*; Muraba, Yoshinori*; Matsuishi, Satoru*; Igawa, Naoki; Kodama, Katsuaki; Shamoto, Shinichi; Hosono, Hideo*

Physical Review B, 84(2), p.024521_1 - 024521_7, 2011/07

https://doi.org/10.1103/PhysRevB.84.024521

Crystal and magnetic structures and properties of BiMnO

Belik, A. A.*; Kodama, Katsuaki; Igawa, Naoki; Shamoto, Shinichi; Kosuda, Kosuke*; Muromachi, Eiji*

Journal of the American Chemical Society, 132(23), p.8137 - 8144, 2010/05

https://doi.org/10.1021/ja102014n

Neutron powder diffraction study on the crystal and magnetic structures of BiCoO

Belik, A. A.*; Iikubo, Satoshi; Kodama, Katsuaki; Igawa, Naoki; Shamoto, Shinichi; Niitaka, Seiji*; Azuma, Masaki*; Shimakawa, Yuichi*; Takano, Mikio*; Izumi, Fujio*; et al.

Chemistry of Materials, 18(3), p.798 - 803, 2006/02

https://doi.org/10.1021/cm052334z

The crystal and magnetic structures of polycrystalline BiCoO have been determined by the Rietveldmethod from neutron diffraction data measured at temperatures from 5 to 520 K. BiCoO (space groupP4mm; Z=1; a=3.72937(7) and c=4.72382(15) at room temperature; tetragonality c/a=1.267) is isotypic with BaTiO and PbTiO in the whole temperature range. BiCoO is an insulator with a Neeltemperature of 470 K. A possible model for antiferromagnetic order is proposed with a propagationvector of k=(1/2, 1/2, 0). In this model, magnetic moments of Co ions are parallel to the c directionand align antiferromagnetically in the ab plane. The antiferromagnetic ab layers stack ferromagneticallyalong the c axis, forming a C-type antiferromagnetic structure. Refined magnetic moments at 5 and 300K are 3.24(2) and 2.93(2), respectively. The structure refinements revealed no deviation fromstoichiometry in BiCoO. BiCoO decomposed in air above 720 K to give CoO and sillenite-like BiCoO.

Preparation and characterization of single-phase SiC nanotubes and C-SiC coaxial nanotubes

Taguchi, Tomitsugu; Igawa, Naoki; Yamamoto, Hiroyuki; Shamoto, Shinichi; Jitsukawa, Shiro

Physica E, 28(4), p.431 - 438, 2005/09

https://doi.org/10.1016/j.physe.2005.05.048

Preparation conditions of single-phase SiC nanotubes and C-SiC coaxial nanotubes were investigated. The characterization of single-phase SiC nanotubes and C-SiC coaxial nanotubes were carried out. The SiC nanowires, which were made of the catenated SiC grains of 50-200 nm in diameter, were obtained in carbon nanotubes reacted at 1450 C. The only C-SiC coaxial nanotubes were formed at 1300 C. A few single-phase SiC nantoubes were synthesized at 1200 C for 100 h. More than half number of nanotubes reacted at 1200 C for 100 h were altered to single-phase SiC nantoubes by heat treatment of 600 C for 1h in air since the remained carbon was removed. The energy dispersive X-ray spectroscopy analysis revealed that the atomic ratio of Si to C in single-phase SiC nanotubes was almost 1; these single-phase SiC nanotubes consisted of near-stoichiometric SiC grains.

Observation of optical signals using optical fibers in operating fission reactor core

Kakuta, Tsunemi; Shikama, Tatsuo*; ; ; Shamoto, Naoki*;

Proc. of Int. Conf. on Optical Technology and Image Processing in Fluid,Thermal and Combustion Flow, p.1 - 5, 1998/00

no abstracts in English

Microstructure observation of SiC/SiC composites dispersed with carbon nanofiber fabricated by conventional processes

Taguchi, Tomitsugu; Hasegawa, Yoshio*; Igawa, Naoki; Shamoto, Shinichi

no journal, , 

The SiC/SiC composites with and without carbon nanofiber (CNF) were fabricated by polymer impregnated and pylorysis (PIP) and chemical vapor infiltration (CVI) processes. Microstructure observations of the SiC/SiC composites with and without CNF were performed. According to TEM observation, neither crack nor pore existed in the interphase between CNF and SiC matrix while some pore was observed in the SiC matrix. The SEM observation of fracture surface indicated that not only pull-out of SiC fibers but also pull-out of CNF were observed in the SiC/SiC composites with CNF.

Synthesis and microstructural observation of carbide ceramic composite nanotubes by surface reforming of carbon nanotubes

Taguchi, Tomitsugu; Igawa, Naoki; Yamamoto, Hiroyuki; Shamoto, Shinichi

no journal, , 

Single-phase SiC and TiC nanotubes were succeeded in synthesized by the reaction of carbon nanotubes with Si powder and Ti powder. The X-ray diffraction patterns indicate that much carbon nanotubes reacted with Si and Ti were transformed to SiC and TiC with increasing the reacting temperature. The results of TEM observation reveal that C-SiC coaxial nanotubes, which are carbon nanotubes sheathed with SiC layer, were synthesized as well as single-phase SiC nanotubes. On the other hand, carbon nanotubes equipped with TiC nano-particles were synthesized in the case of reaction with Ti powder.