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596 results on '"Matsuoka, Masaya"'

1. Stabilization of layered perovskite structures via strontium substitution in Ca$_3$Ti$_2$O$_7$ revealed via elemental mapping

Author

Kurushima, Kosuke, Nakajima, Hiroshi, Mine, Shinya, Tsukasaki, Hirofumi, Matsuoka, Masaya, Gao, Bin, Cheong, Sang-Wook, and Mori, Shigeo

Subjects
Condensed Matter - Materials Science
Abstract

Extensive studies have been performed on layered compounds, ranging from layered cuprates to van der Waals materials with critical issues of intergrowths and stacking faults. However, such structures have been studied less because of experimental difficulty. We present characteristic defect structures of intergrowths in the Ruddlesden-Popper Ca$_{2.46}$Sr$_{0.54}$Ti$_2$O$_7$, which is known to exhibit hybrid improper ferroelectricity. Transmission electron microscopy reveals that numerous intergrowths composed of 7 and 15 layers are introduced in the ferroelectric domains. Elemental maps demonstrate that Sr ions are selectively substituted into the perovskite layers of intergrowths. Density functional theory calculations support the site-selective substitution of Sr ions, favorably located in the intergrowths. The stabilization of the Ruddlesden-Popper phase and intergrowths via Sr substitution can be explained by the ionic-radius difference between Ca and Sr ions. The study reveals detailed defect structures originating from the layered perovskite structure of Ca$_{2.46}$Sr$_{0.54}$Ti$_2$O$_7$, and shows the usefulness of elemental mapping in probing the substitution effects in oxides.

Published
2022
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2. Charged domain boundaries stabilized by translational symmetry breaking in the hybrid improper ferroelectric Ca$_{3-x}$Sr$_x$Ti$_2$O$_7$

Author

Nakajima, Hiroshi, Kurushima, Kosuke, Mine, Shinya, Tsukasaki, Hirofumi, Matsuoka, Masaya, Gao, Bin, Cheong, Sang-Wook, and Mori, Shigeo

Subjects
Condensed Matter - Materials Science
Abstract

Charged domain walls and boundaries in ferroelectric materials display distinct phenomena, such as an increased conductivity due to the accumulation of bound charges. Here, we report the electron microscopy observations of atomic-scale arrangements at charged domain boundaries in the hybrid improper ferroelectric Ca$_{2.46}$Sr$_{0.54}$Ti$_2$O$_7$. Like in the prototype improper ferroelectric YMnO$_3$, we find that charged domain boundaries in Ca$_{2.46}$Sr$_{0.54}$Ti$_2$O$_7$ correspond to out-of-phase boundaries, which separate adjacent domains with a fractional translational shift of the unit cell. In addition, our results show that strontium ions are located at charged domain boundaries. The out-of-phase boundary structure may decrease the polarization charge at the boundary because of the ferrielectric nature of Ca$_{2.46}$Sr$_{0.54}$Ti$_2$O$_7$, thereby promoting the stabilization of the charged state. By combining atomic-resolution imaging and density-functional theory calculations, this study proposes an unexplored stabilization mechanism of charged domain boundaries and structural defects accompanying out-of-phase translational shifts.

Published
2021
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15. Stabilization of layered perovskite structures via strontium substitution in Ca3Ti2O7 revealed via elemental mapping.

Author

Kurushima, Kosuke, Nakajima, Hiroshi, Mine, Shinya, Tsukasaki, Hirofumi, Matsuoka, Masaya, Gao, Bin, Cheong, Sang-Wook, and Mori, Shigeo

Subjects
PEROVSKITE, STRONTIUM, STRONTIUM titanate, TRANSMISSION electron microscopy, DENSITY functional theory, LEAD titanate, CUPRATES
Abstract

Extensive studies have been performed on layered compounds, ranging from layered cuprates to van der Waals materials with critical issues of intergrowths and stacking faults. However, such structures have been studied less because of experimental difficulty. We present characteristic defect structures of intergrowths in the Ruddlesden–Popper Ca2.46Sr0.54Ti2O7, which is known to exhibit hybrid improper ferroelectricity. Transmission electron microscopy reveals that numerous intergrowths composed of 7 and 15 layers are introduced in the ferroelectric domains. Elemental maps demonstrate that Sr ions are selectively substituted into the perovskite layers of intergrowths. Density functional theory calculations support the site-selective substitution of Sr ions, favorably located in the intergrowths. The stabilization of the Ruddlesden–Popper phase and intergrowths via Sr substitution can be explained by the ionic-radius difference between Ca and Sr ions. The study reveals detailed defect structures originating from the layered perovskite structure of Ca2.46Sr0.54Ti2O7 and shows the usefulness of elemental mapping in probing the substitution effects in oxides. [ABSTRACT FROM AUTHOR]

Published
2022
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19. Contributors

Author

Anpo, Masakazu, primary, Belbin, Fiona E., additional, den Besten, Jasper, additional, Comben, Nicholas E., additional, Dodd, Antony N., additional, Endo, Masato, additional, Fang, Wei, additional, Fraser, Donald P., additional, Fukuda, Hirokazu, additional, Fukuda, Naoya, additional, Furukawa, Hajime, additional, Hashimoto, Atsushi, additional, Haubruge, Eric, additional, Horiuchi, Yu, additional, Itoh, Hiromichi, additional, Iwamura, Koji, additional, Janssen, R.J.P., additional, Kameoka, Takaharu, additional, Kataoka, Masataka, additional, Kitaya, Yoshiaki, additional, Krijn, M.P.C.M., additional, Kubota, Chieri, additional, Lin, Yi-Chueh, additional, Masoud, Sara, additional, Matsuoka, Masaya, additional, Meng, Chao, additional, Moriyuki, Shogo, additional, Nakamura, Kenji, additional, Nguyen, Bach Kim, additional, Nicole, Celine C.S., additional, Nishida, Yoshikazu, additional, Oka, Yoshito, additional, Okada, Nobuaki, additional, Ogura, Toichi, additional, Okuda, Kuniharu, additional, Okahara, Satoshi, additional, Shimizu, Hiroshi, additional, Son, Young-Jun, additional, Sugano, Masashi, additional, Sugimura, Nobuhiro, additional, Tanigaki, Yusuke, additional, Thinh, Nguyen Quang, additional, Tronstad, Russell, additional, van den Bergh, T., additional, van Elmpt, R.F.M., additional, van Slooten, Udo, additional, Wada, Teruo, additional, Xu, Yong, additional, Yamamoto, Kazuhiko, additional, Yokoyama, Ryohei, additional, and Zheng, Song, additional

Published
2019
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31. Solar light-driven selective photoelectrochemical CO2 reduction to CO in aqueous media using Si nanowire arrays decorated with Au and Au-based metal nanoparticles.

Author

Horiuchi, Yu, Miyazaki, Keisuke, Tachibana, Mika, Nishigaki, Kenichi, and Matsuoka, Masaya

Subjects
METAL nanoparticles, PHOTOCATHODES, NANOWIRES, SILICON nanowires, GOLD nanoparticles, ELECTROLESS plating, COPPER
Abstract

To address recent energy and environmental issues, such as global warming and resource depletion, significant interest has been shown in carbon dioxide (CO2) fixation based on photoelectrochemical processes under solar light irradiation. The present paper describes the applicability of gold nanoparticles-decorated silicon nanowire arrays (Au/SiNW) as photoelectrodes to promote CO2 reduction. The decoration with Au nanoparticles of SiNW was performed by an electroless plating utilizing surface hydrogen-terminated silicon groups, generated during the nanowire formation process. Au/SiNW exhibits efficient photoelectrochemical performance for CO2 reduction to produce CO selectively in an aqueous medium under simulated solar light irradiation owing to its vertically aligned nanowire structure and Au nanoparticles as cocatalysts. The former provides high specific surface area and light trapping effect, and the latter induces selective interaction with CO2. Moreover, a unique two-steps method for Au decoration that consists of photo-assisted deposition of copper nanoparticles and the following electroless plating to replace Cu atoms to Au ones achieves more uniform decoration of SiNW with highly dispersed core–shell structured Cu@Au nanoparticles. The resulting photoelectrode, termed Cu@Au/SiNW, shows improved selectivity toward CO production and gives a good Faradic efficiency of 72% in an aqueous medium. [ABSTRACT FROM AUTHOR]

Published
2023
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40. Near-Infrared Spectroscopic Analysis─Formation of Ca(OH)2and Ca(OD)2by Hydration of CaO with H2O and D2O

Author

Takeuchi, Masato, Kikuchi, Tadateru, Kondo, Atsushi, Kurosawa, Ryo, Ryu, Junichi, and Matsuoka, Masaya

Abstract

The dehydration behavior of Ca(OH)2was analyzed using near-infrared (NIR) and mid-infrared spectroscopy, with typical absorption bands attributed to the surface and interlayer hydroxyl groups of Ca(OH)2being observed at 7260 and 7083 cm–1in the NIR region, respectively. The dehydration reaction of Ca(OH)2proceeded at approximately 470 °C, resulting in the disappearance of the interlayer hydroxyls of Ca(OH)2and the formation of isolated hydroxyls of the CaO surface (7231 cm–1). The hydration behavior of CaO with H2O was also investigated using NIR spectroscopy, revealing that upon contact with H2O vapor at 50 °C [relative humidity (RH), 55%], CaO was immediately hydrated to form the interlayer hydroxyls of Ca(OH)2after several minutes. Furthermore, since the difference between Ca(OH)2and Ca(OD)2could not be distinguished by X-ray diffraction measurements, the hydration behavior of CaO upon exposure to D2O vapor at room temperature was examined using NIR spectroscopy. This revealed the NIR absorption bands at 5357 and 5259 cm–1, corresponding to the surface and interlayer OD groups of Ca(OD)2, respectively. However, it should be noted that since the dehydration of Ca(OH)2and the hydration of CaO were evaluated under atmospheric conditions, the formation of CaCO3due to CO2adsorption on the CaO surface could not be disregarded.

Published
2023
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