Kumada, Takayuki; Oba, Yojiro; Motokawa, Ryuhei; Morooka, Satoshi; Tominaga, Aki; Tanida, Hajime; Shobu, Takahisa; Konno, Azusa; Owada, Kenji*; Ono, Naoko*; et al.
Journal of Nuclear Materials, 528, p.151890_1 - 151890_7, 2020/01
We have developed an anomalous small-angle X-ray scattering (ASAXS) diffractometer in SPring-8 to investigate irradiation-induced nanostructural change in ion-beam irradiated stainless steel. A thermally-aged MA956 stainless steel sample displays power-law scattering that follows the Porod law at the magnitude of scattering vector, Q, below 0.5 nm and an overlapped shoulder around 0.7 nm. After the ion-beam irradiation, the intensity of the shoulder remained unchanged, whereas that of the power-law scattering nearly doubled. This result indicates that none of the structural parameters of the Cr-rich nanoprecipitates, such as the number density, size, and interface roughness, were changed by the irradiation.
Owada, Kenji*; Tsukada, Shinya*; Fukuda, Tatsuo; Tsutsui, Satoshi*; Baron, A. Q. R.*; Mizuki, Junichiro*; Owa, Hidehiro*; Yasuda, Naohiko*; Terauchi, Hikaru*
Physical Review B, 98(5), p.054106_1 - 054106_10, 2018/08
Kobata, Masaaki; Okane, Tetsuo; Nakajima, Kunihisa; Suzuki, Eriko; Owada, Kenji; Kobayashi, Keisuke*; Yamagami, Hiroshi; Osaka, Masahiko
Journal of Nuclear Materials, 498, p.387 - 394, 2018/01
In this study, for the understandings of Cesium (Cs) adsorption behavior on structure materials in severe accidents at a light water nuclear reactor, the chemical state of Cs and its distribution on the surface of SUS304 stainless steel (SS) with different Si concentration were investigated by hard X-ray photoelectron spectroscopy (HAXPES) and scanning electron microscope / energy dispersive X-ray spectroscopy (SEM/EDX). As a result, it was found that Cs is selectively adsorbed at the site where Si distributes with high concentration. CsFeSiO is a dominant Cs products in the case of low Si content, mainly formed, while CsSiO and CsSiO are formed in addition to CsFeSiO in the case of high Si content. The chemical forms of the Cs compounds produced in the adsorption process on the SS surface has a close correlation with the concentration and chemical states of Si originally included in SS.
Motai, Satoko*; Mukai, Hiroki*; Watanuki, Tetsu; Owada, Kenji; Fukuda, Tatsuo; Machida, Akihiko; Kuramata, Chisaki*; Kikuchi, Ryosuke*; Yaita, Tsuyoshi; Kogure, Toshihiro*
Journal of Mineralogical and Petrological Sciences, 111(5), p.305 - 312, 2016/10
no abstracts in English
Shimizu, Daisuke*; Tsukada, Shinya*; Matsuura, Masato*; Sakamoto, Junya*; Kojima, Seiji*; Namikawa, Kazumichi*; Mizuki, Junichiro; Owada, Kenji
Physical Review B, 92(17), p.174121_1 - 174121_5, 2015/11
The phase diagram and the relationship between the crystal coherence length and electrical response of Pb[(MgNb)Ti]O (PMN-xPT) near the morphotropic phase boundary (MPB) have been precisely investigated using a single crystal with a Ti composition gradient by synchrotron X-ray diffraction and inelastic light scattering at room temperature. The crystal has two boundaries at Ti compositions of 29.0 mol% and 34.7 mol% which correspond to the phase boundaries between the monoclinic B (MB) and C (MC) phases and between the MC and tetragonal (T) phases, respectively. It is shown that there is a strong negative correlation between the electrical response and the crystal coherence length at the sub-m scale. The results are explained by the size effects of domains near the MPB.
Hu, W.*; Hayashi, Koichi*; Fukumura, Tomoteru*; Akagi, Kazuto*; Tsukada, Masaru*; Happo, Naohisa*; Hosokawa, Shinya*; Owada, Kenji; Takahashi, Masamitsu; Suzuki, Motohiro*; et al.
Applied Physics Letters, 106(22), p.222403_1 - 222403_5, 2015/06
Owada, Kenji; Mizuki, Junichiro*; Matsushita, Mitsuyoshi*; Namikawa, Kazumichi*
Physical Review B, 90(10), p.104109_1 - 104109_12, 2014/09
The paraelectric (PE) to ferroelectric (FE) first-order phase transition of 0.91Pb(ZnNb)O-0.09PbTiO ( = 455 K on cooling) has been studied by the complementary use of X-ray diffuse scattering (XDS) and coherent X-ray scattering (CXS). XDS was mainly used to investigate the FE regions, while CXS was mainly used to investigate the PE regions above on cooling. The diffuse scattering intensity due to the appearance of FE regions shows a maximum at K. The diffuse scattering is dynamic in nature and the softening trend changes to a hardening trend at . This means that the FE instability is maximum at and therefore the FE regions are well stabilized below . The spatial autocorrelation function obtained by CXS, corresponding to the texture of PE regions, starts to rapidly change at about and is most unstable at . We conclude that a heterophase fluctuation occurs between and near the phase transition. The heterophase fluctuation can be expected to correlate to the low-frequency dielectric dispersion and contribute to the phase transition as a precursor phenomenon of the first-order phase transition.
Hu, W.*; Hayashi, Koichi*; Owada, Kenji; Chen, J.*; Happo, Naohisa*; Hosokawa, Shinya*; Takahashi, Masamitsu; Bokov, A.*; Ye, Z.-G*
Physical Review B, 89(14), p.140103_1 - 140103_5, 2014/04
Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Yamanouchi, Kaoru*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Togashi, Tadashi*; Fukami, Kenji*; et al.
Journal of Physics B; Atomic, Molecular and Optical Physics, 46(16), p.164006_1 - 164006_6, 2013/08
By introducing 13th- (61.7 nm) and 15th-order harmonics (53.4 nm) of femtosecond laser pulses at 800 nm into an undulator of SCSS (SPring-8 Compact SASE Source) test accelerator at RIKEN, these harmonic pulses were amplified by a factor of more than 10 with a high contrast ratio through the interaction between accelerated electron bunches and the harmonic pulses. From numerical simulations of the amplification processes of high-order harmonic pulses in the undulator, optimum conditions of the electron bunch duration interacting with the high-order harmonic pulses were investigated for generating full-coherent and intense pulses in the extreme ultraviolet wavelength region.
Koatsuryoku No Kagaku To Gijutsu, 23(3), p.245 - 251, 2013/08
Application of coherent X-ray will be one of the main streams in the next generation synchrotron science. Many kinds of the methodologies have been established by using 3rd-generation synchrotron light sources. In this article, the author focuses on a so-called X-ray photon correlation spectroscopy (XPCS), and shows the recent advances in the application of XPCS to relaxor ferroelectrics.
Matsuura, Masato*; Iida, Hiroyuki*; Hirota, Kazuma*; Owada, Kenji; Noguchi, Yuji*; Miyayama, Masaru*
Physical Review B, 87(6), p.064109_1 - 064109_10, 2013/02
Neutron-scattering studies of (BiNa)TiO (BNT) have been performed to elucidate the microscopic mechanism of the broad maximum in the temperature dependence of the dielectric constant at Tm 600 K and the reduction in the piezoelectric properties above the depolarization temperature, 460 480 K. We observed diffuse scattering near the point below 700 K, which competes with the superlattice peak at the M point of the tetragonal phase but coexists with the superlattice peak at the R point of the rhombohedral phase. The diffuse scattering shows an anisotropic Q shape extending along the 100 direction transverse to the scattering vector Q, which is explained by atomic shifts bridging the tetragonal and rhombohedral structures. We propose that the broad maximum in the dielectric constant is associated with a diffusive first-order transition between the competing tetragonal and rhombohedral phases. In addition, we found that the diffuse scattering is reduced for single crystals grown under high oxygen pressure, which suggests an analogy with the central peak in hydrogen-reduced SrTiO. Inelastic neutron scattering near the point reveals a heavily overdamped soft mode similar to those reported in lead-based relaxors, the "waterfall" feature. Moreover, a damped soft transverse acoustic mode is observed for the 100 direction as the anisotropic diffuse scattering, indicating phase instabilities with the same origin as that of the diffuse scattering. The recovery of the soft mode is observed near the depolarization temperature, which coincides with the disappearance of the superlattice peak at the M point. These results indicate that the depolarization and the waterfall feature originate in the dynamic nature of ferroelectric clusters in the coexisting tetragonal/rhombohedral phase.
Nippon Kessho Gakkai-Shi, 54(3), p.147 - 154, 2012/06
It is well known that B-site randomness contributes to the appearance of relaxor phenomena in the lead-based complex perovskite Pb(B'B'')O. But the microscopic mechanism of the effect of B-site randomness on the systems has not been understood yet. Among the Pb(B'B'')O systems, Pb(InNb)O (PIN) has drawn much attention because it can be in the antiferroelectric (AFE), ferroelectric (FE), or relaxor state depending on B-site randomness. We review the recent progress in our understanding of the effect of B-site randomness on PIN from the experimental viewpoint. As a conclusion of the arguments, we also introduce the frustration mechanism in Pb(B'B'')O.
Owada, Kenji; Yamauchi, Toru*; Fujii, Yasuhiko*; Ueda, Yutaka*
Physical Review B, 85(13), p.134102_1 - 134102_4, 2012/04
We have investigated the critical phenomena of the metal-to-insulator (MI) transition of -NaVO. The critical exponent of 0.226(3) and anisotropic diffuse scattering suggest that the MI transition of -NaVO is two-dimensional in nature and that the dimension of the order parameter is not Ising. The non-Ising-like order parameter indicates that the MI transition is not a simple order-disorder type such as that of '-NaVO but charge-density-wave-like, where the valence at each V site is continuous and the arrangement is modulated. This closely corresponds to the situation predicted by neutron diffraction measurements and NMR measurements.
Owada, Kenji; Shimomura, Susumu*; Nakao, Hironori*; Matsushita, Mitsuyoshi*; Namikawa, Kazumichi*; Mizuki, Junichiro
Journal of Physics; Conference Series, 320, p.012086_1 - 012086_5, 2011/09
We have performed an X-ray photon correlation spectroscopy measurement of 91Pb(ZnNb)O-9PbTiO and found a slow structural fluctuation in time near . The slow fluctuation consists of long-term and short-term fluctuations. We have derived the short-term fluctuation from the intensity fluctuations and found out the relaxation time to be an order of 10s. It is suggested that the slow fluctuation is owing to the competition between macroscopic tetragonal symmetry and the microscopic orthorhombic symmetry. The competition should be a main reason for the low-frequency dielectric permittivity.
Owada, Kenji; Fukuda, Tatsuo; Mizuki, Junichiro; Hirota, Kazuma*; Terauchi, Hikaru*; Tsutsui, Satoshi*; Baron, A. Q. R.*; Owa, Hidehiro*; Yasuda, Naohiko*
Journal of the Korean Physical Society, 59(3), p.2509 - 2514, 2011/09
Pb(InNb)O (PIN) can be antiferroelectric (AFE), ferroelectric (FE) or a relaxor depending upon the perovskite B-site randomness. Orderd PIN (O-PIN, without B-site randomness) is supposed to be an ideal system of lead-based complex perovskite Pb(B'B'')O and expected to give us a clear picture of the AFE/relaxor nature of the ground state by the B-site randomness. We studied the dynamics of O-PIN by inelastic X-ray scattering. The quasielastic (QE) scattering shows the critical slowing down and the transverse acoustic (TA) mode shows the softening towards . On the other hand, the transverse optic (TO) mode shows the softening toward low temperature with no clear anomaly at . These results represent that the antiferroelectric (AFE) phase transition is associated with the TA and the origin of the QE scattering, while ferroelectric correlation does exist behind the AFE ordering. The effect of B-site randomness is finally discussed on the basis of the results.
Ishii, Kenji; Ishihara, Sumio*; Murakami, Yoichi*; Ikeuchi, Kazuhiko*; Kuzushita, Kaori*; Inami, Toshiya; Owada, Kenji; Yoshida, Masahiro; Jarrige, I.; Tatami, Naka*; et al.
Physical Review B, 83(24), p.241101_1 - 241101_4, 2011/06
Owada, Kenji; Mizuki, Junichiro; Namikawa, Kazumichi*; Matsushita, Mitsuyoshi*; Shimomura, Susumu*; Nakao, Hironori*; Hirota, Kazuma*
Physical Review B, 83(22), p.224115_1 - 224115_7, 2011/06
Complementary use of coherent X-ray diffraction (CXD), X-ray diffuse scattering, conventional X-ray diffraction techniques and dielectric measurements has enabled us to investigate Pb(ZnNb)O-9%PbTiO with a multiple-length-scale approach from the macroscale (lattice constants, bulk averaged) and microscale to the nanoscale (polar nanoregions (PNRs)) and discuss the contribution of each scale to the dielectric permittivity.
Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Okino, Tomoya*; Yamanouchi, Kaoru*; et al.
Optics Express (Internet), 19(1), p.317 - 324, 2011/01
The 13th harmonic of a Ti:sapphire (Ti:S) laser in the plateau region was injected as a seeding source to a 250-MeV free-electron-laser (FEL) amplifier. When the amplification conditions were fulfilled, strong enhancement of the radiation intensity by a factor of 650 was observed. The random and uncontrollable spikes, which appeared in the spectra of the Self-Amplified Spontaneous Emission (SASE) based FEL radiation without the seeding source, were found to be suppressed drastically to form to a narrow-band, single peak profile at 61.2 nm. The properties of the seeded FEL radiation were well reproduced by numerical simulations. We discuss the future precept of the seeded FEL scheme to the shorter wavelength region.
Owada, Kenji; Tomita, Yusuke*
Nippon Butsuri Gakkai-Shi, 65(10), p.800 - 804, 2010/10
no abstracts in English
Nakao, Hironori*; Owada, Kenji; Shimomura, Susumu*; Ochiai, Akira*; Namikawa, Kazumichi*; Mizuki, Junichiro; Mimura, Hidekazu*; Yamauchi, Kazuto*; Murakami, Yoichi*
AIP Conference Proceedings 1234, p.935 - 938, 2010/06