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Journal Articles

Short- and middle-ranges order structures of KNbO$$_3$$ nanocrystals

Yoneda, Yasuhiro; Kunisada, Ryoichi*; Chikada, Tsukasa*; Ueno, Shintaro*; Fujii, Ichiro*; Nagata, Hajime*; Ohara, Koji*; Wada, Satoshi*

Japanese Journal of Applied Physics, 58(SL), p.SLLA03_1 - SLLA03_7, 2019/11

 Times Cited Count:0 Percentile:100(Physics, Applied)

Journal Articles

Local structure and phase transitions of KNbO$$_3$$

Yoneda, Yasuhiro; Ohara, Koji*; Nagata, Hajime*

Japanese Journal of Applied Physics, 57(11S), p.11UB07_1 - 11UB07_6, 2018/11

 Times Cited Count:5 Percentile:53.96(Physics, Applied)

Local structure analysis of KNbO$$_3$$, which is the parent compound for lead-free piezoelectric materials, have been performed by X-ray pair-distribution functions (PDF). The refinements of local structure in wide temperature ranges indicates that only the rhombohedral structure can describe the observed bond distributions within the unit cell. The rhombohedral distortion maintained locally in all four phases.

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:73.87(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

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:2 Percentile:73.27(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 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:7 Percentile:65.2(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

The H-Invitational Database (H-InvDB); A Comprehensive annotation resource for human genes and transcripts

Yamasaki, Chisato*; Murakami, Katsuhiko*; Fujii, Yasuyuki*; Sato, Yoshiharu*; Harada, Erimi*; Takeda, Junichi*; Taniya, Takayuki*; Sakate, Ryuichi*; Kikugawa, Shingo*; Shimada, Makoto*; et al.

Nucleic Acids Research, 36(Database), p.D793 - D799, 2008/01

 Times Cited Count:50 Percentile:24.18(Biochemistry & Molecular Biology)

Here we report the new features and improvements in our latest release of the H-Invitational Database, a comprehensive annotation resource for human genes and transcripts. H-InvDB, originally developed as an integrated database of the human transcriptome based on extensive annotation of large sets of fulllength cDNA (FLcDNA) clones, now provides annotation for 120 558 human mRNAs extracted from the International Nucleotide Sequence Databases (INSD), in addition to 54 978 human FLcDNAs, in the latest release H-InvDB. We mapped those human transcripts onto the human genome sequences (NCBI build 36.1) and determined 34 699 human gene clusters, which could define 34 057 protein-coding and 642 non-protein-coding loci; 858 transcribed loci overlapped with predicted pseudogenes.

Journal Articles

High performance tokamak experiments with a ferritic steel wall on JFT-2M

Tsuzuki, Kazuhiro; Kimura, Haruyuki; Kawashima, Hisato; Sato, Masayasu; Kamiya, Kensaku; Shinohara, Koji; Ogawa, Hiroaki; Hoshino, Katsumichi; Bakhtiari, M.; Kasai, Satoshi; et al.

Nuclear Fusion, 43(10), p.1288 - 1293, 2003/10

 Times Cited Count:37 Percentile:24.25(Physics, Fluids & Plasmas)

no abstracts in English

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.

Oral presentation

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

Yoneda, Yasuhiro; Nagamoto, Takeru*; Nagata, Hajime*; Kobune, Masafumi*

no journal, , 

Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ (BNT) is a candidate for lead-free piezoelectric material having a perovskite-type structure. The crystal structure of BNT was believed to be rhombohedral. Recently, BNT grown by high-temperature synthesis was reported to be monoclinic. We have synthesized Bi$$_ {0.5} $$Na$$_ {0.5} $$TiO$$_3$$ crystal in the high temperature condition so as to apply the Rietveld method for average structure refinement and the atomic pair-distribution function (PDF) technique for local structure refinement. The Bragg peaks can be reproduced by assuming a monoclinic structure, while the local structure can be reproduced by assuming a rhombohedral crystal structure.

Oral presentation

Local structure analysis of KNbO$$_3$$ by high-energy X-ray diffraction

Yoneda, Yasuhiro; Ohara, Koji*; Nagata, Hajime*

no journal, , 

KNbO$$_3$$ has been a candidate for the end member of a non-Pb ferroelectric materials. We performed local structure analysis of KNbO$$_3$$ bulk ceramics by high-energy synchrotron X-ray measurements. It has recently established that temperature-driven structural phase transitions in several perovskite ferroelectric materials (PbTiO$$_3$$, BaTiO$$_3$$, and NaNbO$$_3$$) believed to be purely displacive, have a significant order-disorder component. We performed the local structure analysis in a wide-temperature range to observe order-disorder feature of KNbO$$_3$$. The lowest temperature structure of KNbO$$_3$$ is rhombohedral, and we found that the local rhombohedral distortion maintained in the high-temperature cubic phase.

Oral presentation

Local structure and phase transitions of KNbO$$_3$$

Yoneda, Yasuhiro; Ohara, Koji*; Nagata, Hajime*

no journal, , 

no abstracts in English

12 (Records 1-12 displayed on this page)
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