Yoneda, Yasuhiro; Noguchi, Yuji*
Japanese Journal of Applied Physics, 59(SP), p.SPPA01_1 - SPPA01_7, 2020/11
We investigate A-site cation ordering in the ferroelectric perovskite BiNaTiO (BNT) by synchrotron X-ray total scattering. Although BNT has a problem of a low depolarization temperature, it is promising a lead-free piezoelectric material. Since the depolarization temperature is presumed to correspond to a relaxer like gradual order-disorder phase transition, local structure analysis is necessary to understand the structure of the diorder phase. Through this approach, the elusive connection between chemical heterogeneity and structural heterogeneity is revealed. Because of the large randomness, the Ti off-center shift is averaged out beyond the unit cell and the structure becomes very close to the average structure beyond the unit cell.
Fujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Watanabe, Shinta*; Kamada, Kei*; Okano, Yasuaki*; Kato, Masahiro*; Hosaka, Masahito*; et al.
Applied Physics Express, 13(8), p.085505_1 - 085505_4, 2020/08
To clarify the existence of cation vacancies in Ce-doped GdAlGaO (Ce:GAGG) scintillators, we performed gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS). GiPAL spectra of GAGG and Ce:GAGG comprised two exponential decay components, which were assigned to positron annihilation at bulk and defect states. By an analogy with Ce:YAlO, the defect-related component was attributed to Al/Ga-O divacancy complexes. This component was weaker for Ce, Mg:GAGG, which correlated with the suppression of shallow electron traps responsible for phosphorescence. Oxygen vacancies were charge compensators for Al/Ga vacancies. The lifetime of the defect-related component was significantly changed by Mg co-doping. This was understood by considering aggregates of Mg ions at Al/Ga sites with oxygen vacancies, which resulted in the formation of vacancy clusters.
Okayasu, Satoru; Harii, Kazuya*; Kobata, Masaaki; Yoshii, Kenji; Fukuda, Tatsuo; Ishida, Masahiko*; Ieda, Junichi; Saito, Eiji
Journal of Applied Physics, 128(8), p.083902_1 - 083902_7, 2020/08
Oba, Masaki; Miyabe, Masabumi; Akaoka, Katsuaki; Wakaida, Ikuo
Japanese Journal of Applied Physics, 59(6), p.062001_1 - 062001_6, 2020/06
Using a semiconductor microwave source and a coaxial cable for microwave transmission, a compact microwave-assisted, laser-induced breakdown spectroscopy system without a microwave cavity or waveguide was developed. Several types of electrode heads were tested, so that the emission intensity was 50 times larger than without microwave. The limit of the enhancement effect was also found.
Puebla, J.*; Xu, M.*; Rana, B.*; Yamamoto, Kei; Maekawa, Sadamichi*; Otani, Yoshichika*
Journal of Physics D; Applied Physics, 53(26), p.264002_1 - 264002_7, 2020/06
Japanese Journal of Applied Physics, 59(5), p.050501_1 - 050501_9, 2020/05
This paper describes the decommissioning work being undertaken at the Fukushima Daiichi Nuclear Power Station of the Tokyo Electric Power Company Holdings Inc.'s (FDNPS) using remote controlled robotic systems, as well as lessons learned from past remote task executions. We also summarize the issues to be considered in promoting safe, steady, and efficient decommissioning based on past experiences. In response to these issues, we are developing test methods for performance evaluation of the robots for nuclear decommissioning, robot simulator for operator proficiency training, and information generation methods to improve the operator's status awareness. The current status of technological development is also described.
Koyama, Tomohiro*; Ieda, Junichi; Chiba, Daichi*
Applied Physics Letters, 116(9), p.092405_1 - 092405_5, 2020/03
Ishikawa, Norito; Taguchi, Tomitsugu*; Kitamura, Akane; Szenes, G.*; Toimil-Molares, M. E.*; Trautmann, C.*
Journal of Applied Physics, 127(5), p.055902_1 - 055902_7, 2020/02
Hillock formation is one of the important aspects of radiation-induced modification of solid material. To our knowledge this is first result showing that the hillock formation in ceramics is affected by the velocity effect. The present result include Se-dependences of hillock dimensions based on precise measurement using TEM (transmission electron microscopy). The paper should be published to make researchers aware that hillock size is actually comparable to ion-track size in wide Se range. In addition, the results include important insight about the hillock formation mechanism of ceramics irradiated with swift heavy ions.
Tsuru, Tomohito; Wakeda, Masato*; Suzudo, Tomoaki; Itakura, Mitsuhiro; Ogata, Shigenobu*
Journal of Applied Physics, 127(2), p.025101_1 - 025101_9, 2020/01
We explored softening/strengthening behavior in various solute in W matrix by density functional theory (DFT) calculations combined with solid solution model. As a result of DFT calculations for various solute, a clear trend was observed in the interaction energy between a solute and a screw dislocation, which has predominant influence on solid solution behavior. The predictions based on the solid solution model with DFT can reasonably reproduce the complicated softening/strengthening as a function of temperature and solute concentration. We conclude that this specific balance is the origin of macroscopic solid solution softening.
Ito, Takashi; Higemoto, Wataru; Koda, Akihiro*; Shimomura, Koichiro*
Applied Physics Letters, 115(19), p.192103_1 - 192103_4, 2019/11
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
Matsuya, Yusuke; Kai, Takeshi; Yoshii, Yuji*; Yachi, Yoshie*; Naijo, Shingo*; Date, Hiroyuki*; Sato, Tatsuhiko
Journal of Applied Physics, 126(12), p.124701_1 - 124701_8, 2019/09
Biological effects after ionizing radiation exposure arise from initial DNA strand breaks. DNA damage can be estimated from the simulation with both track structure analysis and diffusion of free radicals; however, the simulation is a time-consuming process. In this study, we present a simple model for estimating yields of strand breaks based only on spatial patterns of inelastic interactions (i.e., ionization and electronic excitation) generated by electrons, which are evaluated by PHITS code without considering the production and diffusion of free radicals. In this model, the number of events per track and that of the two events pair within 3.4 nm (corresponding to 10 base pair) were stochastically sampled for calculating SSB and DSB yields, respectively. The calculated results agreed well with other simulations and experimental data on DSB yield and yield ratio of DSB/SSB for the exposure to mono-energetic electrons. The present model also can demonstrate the relative biological effectiveness at the DSB endpoint for various photon exposures. This study indicated that the spatial pattern of inelastic events composed of ionization and electronic excitation is sufficient to obtain the impact of electrons on initial induction to DNA strand break.
Journal of Applied Physics, 126(12), p.123904_1 - 123904_8, 2019/09
We have reinvestigated the magnetization reversal in perovskites LaPrCrO, GdCrO, and TmCrO and show that spin rotation or reorientation plays a key role in this property. The magnetization measurements on all systems show the appearance and disappearance of the reversal are commonly depend on a strength of a Zeeman energy at the rare earth site in analogy with spin rotation in GdCrO and TmCrO, denoted at the spin reorientation. Magnetic susceptibility measurements point to either superparamagnetic or single-molecule-magnet-like glassy behavior in all three systems, which is likely linked to a rotation of the R-Cr coupling, as seen from magnetocalorimetry ( = LaPr, Gd, and Tm). We also present a characteristic magnetization switching by rotating the R moments with the aid of large Zeeman energies.
Terasawa, Tomoo; Taira, Takanobu*; Yasuda, Satoshi; Obata, Seiji*; Saiki, Koichiro*; Asaoka, Hidehito
Japanese Journal of Applied Physics, 58(SI), p.SIIB17_1 - SIIB17_6, 2019/08
Chemical vapor deposition (CVD) on substrates with low C solubility such as Cu and Au is promising to grow monolayer graphene selectively in a large scale. Hydrogen is often added to control the domain size of graphene on Cu, while Au does not require H since Ar is inert against oxidation. The effect of H should be revealed to improve the quality of graphene on Au. Here we report the effect of H on the CVD growth of graphene on Au substrates using in situ radiation-mode optical microscopy. The in situ observation and ex situ Raman spectroscopy revealed that whether H was supplied or not strongly affected the growth rate, thermal radiation contrast, and compressive strain of graphene on Au. We attributed these features to the surface reconstruction of Au(001) depending on H supply. Our results are essential to achieve the graphene growth with high quality on Au for future applications.
Fukuda, Takashi*; Yamaguchi, Takashi*; Kakeshita, Tomoyuki*; Harjo, S.; Nakamoto, Tatsushi*
Journal of Applied Physics, 126(2), p.025107_1 - 025107_6, 2019/07
Imai, Masaki; Chudo, Hiroyuki; Ono, Masao; Harii, Kazuya; Matsuo, Mamoru; Onuma, Yuichi*; Maekawa, Sadamichi; Saito, Eiji
Applied Physics Letters, 114(16), p.162402_1 - 162402_4, 2019/04
Arisawa, Hiroki*; Daimon, Shunsuke*; Oikawa, Yasuyuki*; Seo, Y.-J.*; Harii, Kazuya; Oyanagi, Koichi*; Saito, Eiji
Applied Physics Letters, 114(12), p.122402_1 - 122402_5, 2019/03
Fukaya, Yuki; Kawasuso, Atsuo*; Ichimiya, Ayahiko*; Hyodo, Toshio*
Journal of Physics D; Applied Physics, 52(1), p.013002_1 - 013002_19, 2019/01
no abstracts in English
Yoneda, Yasuhiro; Ohara, Koji*; Nagata, Hajime*
Japanese Journal of Applied Physics, 57(11S), p.11UB07_1 - 11UB07_6, 2018/11
Local structure analysis of KNbO, 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.
Imai, Masaki; Ogata, Yudai*; Chudo, Hiroyuki; Ono, Masao; Harii, Kazuya; Matsuo, Mamoru*; Onuma, Yuichi*; Maekawa, Sadamichi; Saito, Eiji
Applied Physics Letters, 113(5), p.052402_1 - 052402_3, 2018/07