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Noguchi, Yuji*; Aso, Seiyu*; Oyama, Kenji*; Ishigaki, Toru*; Yoneda, Yasuhiro; Matsuo, Hiroki*
Physical Review B, 111(21), p.214113_1 - 214113_13, 2025/06
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)We explore the electronic structure of high-quality bismuth sodium titanate (Bi
NaTiO
) powders through a comprehensive approach combining the maximum entropy method (MEM)/Rietveld analysis of synchrotron radiation X-ray diffraction data collected at 200 K with density functional theory (DFT) calculations. We conclude that the covalent Bi-O bond and the resultant ferroelectricity stem primarily from the Bi-6p-O3-2p orbital interaction mediated through Ti-3d.
phases in undoped and Ca-modified sodium niobatesAso, Seiyu*; Matsuo, Hiroki*; Yoneda, Yasuhiro; Morikawa, Daisuke*; Tsuda, Kenji*; Oyama, Kenji*; Ishigaki, Toru*; Noguchi, Yuji*
Physical Review B, 111(17), p.174114_1 - 174114_12, 2025/05
Times Cited Count：1 Percentile：64.20(Materials Science, Multidisciplinary)We investigate the crystal structures, phase transitions, and phase stability of undoped and Ca-modified NaNbO
through a combined analysis of high-resolution synchrotron radiation X-ray and neutron diffraction, convergent-beam electron diffraction, and density functional theory (DFT) calculations. It is demonstrated that the antiferroelectric (AFE)- phase is stabilized over a wide temperature range of 200 to 800 K by Ca modification, and that the NaNbO is stabilized by temperature-driven isostatic pressure accompanied by lattice expansion, whereas the Ca-modified NaNbO is induced by composition-induced chemical pressure along with lattice shrinkage.
Matsuo, Yoichi*; Hase, Yoshihiro; Takeshita, Hiroki*; Notomi, Asako*
JAEA-Review 2014-050, JAEA Takasaki Annual Report 2013, P. 111, 2015/03
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Matsuo, Yoichi*; Takeshita, Hiroki*; Notomi, Asako*; Hase, Yoshihiro; Nozawa, Shigeki*
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Tanaka, Yoshiki*; Notomi, Asako*; Takeshita, Hiroki*; Matsuo, Yoichi*; Hase, Yoshihiro
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Tanaka, Yoshiki*; Matsuo, Yoichi*; Hase, Yoshihiro; Notomi, Asako*; Takeshita, Hiroki*
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Notomi, Asako*; Matsuo, Yoichi*; Hase, Yoshihiro; Takeshita, Hiroki*; Tanaka, Yoshiki*
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Tanaka, Yoshiki*; Notomi, Asako*; Matsuo, Yoichi*; Takeshita, Hiroki*; Hase, Yoshihiro
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Matsuo, Yoichi*; Notomi, Asako*; Hase, Yoshihiro; Takeshita, Hiroki*; Tanaka, Yoshiki*
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ceramicsKuwata, Kenta*; Matsuo, Hiroki*; Noguchi, Yuji*; Yoneda, Yasuhiro
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Barium titanate (BaTiO) is doped with transition metal (TM) ions such as Ni, which act as acceptors to trap electronic carriers (electrons or holes) generated by reductive calcination. In this study, we fabricated BaTiO ceramics co-doped with Dy and La and evaluated their ferroelectric and photovoltaic properties. It was found that the Ni valence can be controlled by Dy/Ni co-doping and that the visible photovoltaic effect can be enhanced by introducing impurity levels derived from Ni-3d.
in high-temperature phaseAso, Seiyu*; Matsuo, Hiroki*; Noguchi, Yuji*; Yoneda, Yasuhiro; Morikawa, Daisuke*; Tsuda, Kenji*
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Recently, higher energy storage density than that of typical ferroelectric BaTiO has been achieved in NaNbO-based antiferroelectrics by utilizing the electric-field-induced phase transition between the antiferroelectric (AFE) and ferroelectric (FE) phases. In this study, we attempted to identify the space group using synchrotron X-ray diffraction and convergent electron diffraction in order to elucidate the full picture of the phase transition behavior in NaNbO and Ca-doped NaNbO. On the other hand, the Ca-doped sample showed that the space group is Pnma, which is consistent with the results obtained by convergent electron diffraction measurements.
Matsuo, Yoichi*; Hase, Yoshihiro; Nozawa, Shigeki; Ishiji, Kotaro*; Takeshita, Hiroki*
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Iwai, Hiroki; Nakamura, Yasuyuki; Matsuo, Hidehiko; Mizui, Hiroyuki; Sano, Kazuya
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Matsuo, Kimihiko*; Ishitobi, Tatsuhiko*; Oka, Hiroshi*; Iwai, Hiroki; Matsuo, Hidehiko; Nakamura, Yasuyuki; Sano, Kazuya
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Iwai, Hiroki; Sano, Kazuya; Mizui, Hiroyuki; Nakamura, Yasuyuki; Hayashi, Kenta; Ishitobi, Tatsuhiko*; Matsuo, Kimihiko*; Oka, Hiroshi*
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Noguchi, Suzunosuke*; Yoneda, Yasuhiro; Matsuo, Hiroki*; Noguchi, Yuji*
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The solid solution Bi
NaBa
TiO (BNT-BT) of the lead-free perovskite ferroelectrics Bi
NaTiO (BNT, space group: R3c) and BaTiO (BT, space group: P4mm) is morphotropic phase boundary (MPB) and has attracted much attention because of its excellent piezoelectricity at MPB. In this study, we aim to control the electric field-induced phase transition and to complete the two-dimensional phase diagram of BNT-BT ceramics before and after the application of an electric field. The dielectric P4bm phase was found to be stabilized at a composition near MPB and with large A-site vacancies in BNT-BT solid solution ceramics.
Fukushima, Kento*; Yoneda, Yasuhiro; Matsuo, Hiroki*; Noguchi, Yuji*
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A lead-free perovskite ferroelectric, (Bi,Na)TiO (rhombohedral R3c), has attracted much attention because it forms a morphotropic phase boundary (MPB) with a tetragonal P4mm ferroelectric [BaTiO, (Bi,K)TiO] and shows excellent piezoelectricity in the MPB. P4bm phase, which exhibits ferri-dielectricity in the vicinity of the MPB, has been found to exist. In this study, we aim to clarify the compositional phase diagram of (Bi,Na)TiO-based solid solution ceramics with strict composition control and to elucidate the whole picture of their polarization properties. bm and the phase boundary between P4bm and P4mm were identified.
K)TiO-(BiLi)TiO solid solutionSaito, Kotaro*; Yoneda, Yasuhiro; Matsuo, Hiroki*; Noguchi, Yuji*
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In addition to excellent piezoelectricity and dielectric properties, ferri-dielectric phases exhibit giant electric-field-induced strain due to the electric-field-induced phase transition. The presence of ferri-dielectric phase and its properties were investigated for (BiK)TiO-(BiLi)TiO (BKT-BLT) solid solution ceramics by searching for compositional phase boundaries and evaluating the composition dependence of polarization properties through crystal structure analysis. This study revealed that a ferri-dielectric phase exists around 
= 8% in the BKT-BLT solid solution system, and that a specifically high relative permittivity can be obtained at this composition.
Aso, Seiyu*; Yoneda, Yasuhiro; Matsuo, Hiroki*; Noguchi, Yuji*
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We have attempted to introduce positive chemical pressure into NaNbO by replacing Na
with a small Ca
. The superlattice reflections originating from the antiferroelectric P phase appeared both before and after the application of an electric field, which confirmed that a reversible electric-field-induced phase transition was achieved.
Matsuo, Yoichi*; Hase, Yoshihiro; Nozawa, Shigeki; Takeshita, Hiroki*; Notomi, Asako*
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