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Journal Articles

Local structure analysis of Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$

Yoneda, Yasuhiro; Nagata, Hajime*; Takenaka, Tadashi*

Journal of the Korean Physical Society, 66(9), p.1339 - 1343, 2015/05

 Times Cited Count:4 Percentile:40.64(Physics, Multidisciplinary)

The potential lead-free piezoelectric material bismuth sodium titanate, Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ (BNT), was investigated by means of high-energy synchrotron X-ray diffraction. BNT has been assumed thus far to exhibit the rhombohedral space group $$R3c$$ at room temperature. Recently, the average structure of BNT was described by the monoclinic space group $$Cc$$. We performed local structure analysis of BNT using atomic pair-distribution function method. The ground state of BNT was found to be rhombohedral structure in which bismuth and sodium atoms were chemically ordered in the perovskite ${it A}$-site.

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

Local structure analysis of Li-substituted (Bi$$_{0.5}$$Na$$_{0.5}$$)TiO$$_3$$ and NaNbO$$_3$$

Yoneda, Yasuhiro; Aoyagi, Rintaro*; Fu, D.*; Takenaka, Tadashi*

Transactions of the Materials Research Society of Japan, 39(3), p.247 - 250, 2014/09

Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ and NaNbO$$_3$$ are ${it AB}$O$$_3$$ perovskite ferroelectric materials and they are considered to be promising lead-free ferroelectric materials because of their relatively high piezoelectric properties in lead-free piezoelectric ceramics. The purpose of this work was to clarify the local structures of Li-substituted Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ and NaNbO$$_3$$ to elucidate the mechanism of the stabilization of the ordered ferroelectric phase.

Journal Articles

Local structure of Li-substituted (Bi$$_{0.5}$$Na$$_{0.5}$$)TiO$$_3$$

Yoneda, Yasuhiro; Hiruma, Yuji*; Nagata, Hajime*; Takenaka, Tadashi*

Japanese Journal of Applied Physics, 49(9), p.09ME09_1 - 09ME09_4, 2010/10

 Times Cited Count:12 Percentile:45.91(Physics, Applied)

(Ba$$_{0.5}$$Na$$_{0.5}$$)TiO$$_3$$ was carried out by a synchrotron radiation X-ray pair-distribution function (PDF) method. The PDF peak is resolved as a doublet owing to the presence of two phases with distinct local structures, those are rhombohedral and tetragonal phases. The dominant rhombohedral phase is stabilized by the Li substitution. The depolarization temperature ($$T_d$$) is increased as increasing the rhombohedral component in the local structure.

Journal Articles

Effect of solute elements in Ni alloys on blistering under He$$^{+}$$ D$$^{+}$$ ion irradiation

Wakai, Eiichi; Ezawa, Tadashi*; Takenaka, Tsuyoshi*; Imamura, Junko*; Tanabe, Tetsuo*; Oshima, Ryuichiro*

Journal of Nuclear Materials, 367-370(1), p.478 - 482, 2007/08

 Times Cited Count:7 Percentile:47.42(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Solid spallation target materials development

Kawai, Masayoshi*; Furusaka, Michihiro; Li, J.-F.*; Kawasaki, Akira*; Yamamura, Tsutomu*; Mehmood, M.*; Kurishita, Hiroaki*; Kikuchi, Kenji; Takenaka, Nobuyuki*; Kiyanagi, Yoshiaki*; et al.

Proceedings of ICANS-XVI, Volume 3, p.1087 - 1096, 2003/07

In order to establish the technique fabricating a thin target slab with a real size, thin tantalum-clad tungsten slab with a hole for a thermocouple was fabricated with the high-precision machinery techniques and the HIP'ing method. The ultrasonic diagnostic showed that tantalum and tungsten bond was perfect. The HIP optimum condition was certified by means of the small punch test as already reported. The electrolytic coating technique in a molten salt was developed to make a thinner tantalum cladding on a tungsten target with a complicated shape, in order to reduce radioactivity from tantalum in an irradiated target.

Journal Articles

R&D of a MW-class solid-target for spallation neutron source

Kawai, Masayoshi*; Furusaka, Michihiro*; Kikuchi, Kenji; Kurishita, Hiroaki*; Watanabe, Ryuzo*; Li, J.*; Sugimoto, Katsuhisa*; Yamamura, Tsutomu*; Hiraoka, Yutaka*; Abe, Katsunori*; et al.

Journal of Nuclear Materials, 318, p.35 - 55, 2003/05

R&D works for MW class solid target composed of tungsten to produce pulsed intense neutron source has been made in order to construct a future scattering facility. Three methods were investigated to prevent corrosion of tungsten from water; those are hipping, brazing and electric coating in molten salt bath. Hipping condition was optimized to be 1500 degree C in the previous work: here small punch test shows highest load for crack initiation of hipped materials at the boundary of W/Ta. The basic techniques for the other two methods were developed. Erosion test showed that uncovered W is susceptible of flowing water velocity. At high velocity w is easy to be eroded. For solid target design slab type and rod type targets were studied. As long as the optimized neutron performance is concerned, 1MW solid target is better than mercury target.

Journal Articles

Effect of solute atoms on swelling in Ni alloys and pure Ni under He$$^{+}$$ ion irradiation

Wakai, Eiichi; Ezawa, Tadashi*; Imamura, Junko*; Takenaka, Tsuyoshi*; Tanabe, Tetsuo*; Oshima, Ryuichiro*

Journal of Nuclear Materials, 307-311(Part.1), p.367 - 373, 2002/12

 Times Cited Count:29 Percentile:84.19(Materials Science, Multidisciplinary)

no abstracts in English

Oral presentation

Progress in development of intense materials against radiation and beam impact, 5; Rapid cooling test of HIPed Ta-cladded W target

Takenaka, Nobuyuki*; Kikuchi, Kenji; Kiyanagi, Yoshiaki*; Kawai, Masayoshi*; Li, J.-F.*; Igarashi, Tadashi*

no journal, , 

Ta-cladded W is manufactured by HIP method for a proto type solid target in intensified high-energy proton targetary. We have carried the thermal shock test of the target model under the rapid cooling conditions by changing temperatures of target itself and cooling water. At a time of loss of coolant a targetary will be heated by decay heat over kW. Then technical issue is how to recover cooling water without giving damage joint layer between Ta and W. It is confirmed that targetary has no damage if it will be cooled below heated up to 500$$^{circ}$$C.

Oral presentation

Substitution effect of Li in Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$

Yoneda, Yasuhiro; Hiruma, Yuji*; Nagata, Hajime*; Takenaka, Tadashi*

no journal, , 

Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ is paid to attention as an alternative material of PbTiO$$_3$$ for the use of an piezoelectric oscillator. In the problem in use as the piezoelectric vibrator, the depolarization temperature is a low. A lot of attempts to increase the depolarization temperature have been performed. Being able to raise the depolarization temperature as an additive only is a lithium. We performed the structure analysis to clarify the T$$_d$$ increasing mechanism on Li-doped i$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$. As a result, Randomness owing to the deference between the ionic size of Na and Bi decreases from the structure though Li is doping done, and it has been understood that the order structure is predominant.

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