Origin of ferroelectric polarization in bismuth sodium titanate

Noguchi, Yuji*; Aso, Seiyu*; Oyama, Kenji*; Ishigaki, Toru*; Yoneda, Yasuhiro; Matsuo, Hiroki*

Physical Review B, 111(21), p.214113_1 - 214113_13, 2025/06

https://doi.org/10.1103/f1l8-6g3f

We explore the electronic structure of high-quality bismuth sodium titanate (BiNaTiO) 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.

Annual report on the environmental radiation monitoring around the Tokai Reprocessing Plant FY2023

Kokubun, Yuji; Hosomi, Kenji; Nagaoka, Mika; Seya, Natsumi; Inoue, Kazumi; Koike, Yuko; Uchiyama, Rei; Sasaki, Kazuki; Maehara, Yushi; Matsuo, Kazuki; et al.

JAEA-Review 2024-054, 168 Pages, 2025/03

JAEA-Review-2024-054.pdf:2.73MB

The Nuclear Fuel Cycle Engineering Laboratories conducts environmental radiation monitoring around the reprocessing plant in accordance with the "Safety Regulations for Reprocessing Plant of JAEA, Part IV: Environmental Monitoring". This report summarizes the results of environmental radiation monitoring conducted during the period from April 2023 to March 2024 and the results of dose calculations for the surrounding public due to the release of radioactive materials from the plant into the atmosphere and ocean. In the results of the above environmental radiation monitoring, several items were affected by radioactive materials emitted from the accident at the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company, Incorporated (changed to Tokyo Electric Power Holdings, Inc. on April 1, 2016), which occurred in March 2011. In addition, environmental monitoring plan, analysis and measurement methods, monitoring data and their chronological change, meteorological data after statistical processing, status of radioactive waste release and evaluation results of the data over the normal range are included as appendices.

Annual report on the environmental radiation monitoring around the Tokai Reprocessing Plant FY2022

Kokubun, Yuji; Nakada, Akira; Seya, Natsumi; Koike, Yuko; Nemoto, Masashi; Tobita, Keiji; Yamada, Ryohei*; Uchiyama, Rei; Yamashita, Daichi; Nagai, Shinji; et al.

JAEA-Review 2023-046, 164 Pages, 2024/03

JAEA-Review-2023-046.pdf:4.2MB

The Nuclear Fuel Cycle Engineering Laboratories conducts environmental radiation monitoring around the reprocessing plant in accordance with the "Safety Regulations for Reprocessing Plant of JAEA, Part IV: Environmental Monitoring". This report summarizes the results of environmental radiation monitoring conducted during the period from April 2022 to March 2023 and the results of dose calculations for the surrounding public due to the release of radioactive materials into the atmosphere and ocean. In the results of the above environmental radiation monitoring, many items were affected by radioactive materials emitted from the accident at the Fukushima Daiichi Nuclear Power Plant of Tokyo Electric Power Company, Incorporated (changed to Tokyo Electric Power Company Holdings, Inc. on April 1, 2016), which occurred in March 2011. Also included as appendices are an overview of the environmental monitoring plan, an overview of measurement methods, measurement results and their changes over time, meteorological statistics results, radioactive waste release status, and an evaluation of the data which deviated of the normal range.

Nanoscale structural analysis of BiNaTiO in high-temperature phases

Yoneda, Yasuhiro; Noguchi, Yuji*

Japanese Journal of Applied Physics, 60(SF), p.SFFA08_1 - SFFA08_10, 2021/11

https://doi.org/10.35848/1347-4065/ac19fd

BiNaTiO (abbreviated as BNT) is a lead-free material but exhibits relatively large piezoelectric properties, a lot of researches have been conducted. We performed local structural analysis using high-quality BNT with a stoichiometrically correct composition, and found a chemical order structure of Bi/Na in locally. BNT undergoes a phase transition to a cubic phase at 400C. We estimated that a new disorder structure will appear in the high-temperature phase. In the high temperature phase, pair distribution function (PDF) analysis using synchrotron radiation high-energy X-rays was performed. As a result, we found that Bi shifts from 200C, and this shift becomes an order parameter for the phase transition.

Nanoscale structural analysis of Pb(MgNb)O

Yoneda, Yasuhiro; Taniguchi, Hiroki*; Noguchi, Yuji*

Journal of Physics; Condensed Matter, 33(3), p.035401_1 - 035401_8, 2021/01

https://doi.org/10.1088/1361-648X/abb866

Nanoscale structural analysis of relaxor Pb(MgNb)O (PMN) was performed using synchrotron high-energy X-ray diffraction measurements. Although PMN is a well-known relaxor ferroelectric material, the average structure is a cubic structure, and various models have been proposed to explain the ferroelectric microstructure. We performed a wide-range local structure analysis up to 20 nm using the pair distribution function (PDF). As a result, it was found that the structure of PMN changed depending on the distance and it was a glass-like structure.

Local structure analysis of PbTiO in high-temperature cubic phase

Yoneda, Yasuhiro; Taniguchi, Hiroki*; Kitanaka, Yuki*; Noguchi, Yuji*

Ferroelectrics, 538(1), p.57 - 62, 2019/05

https://doi.org/10.1080/00150193.2019.1569986

High-energy X-ray diffraction study was performed on lead titanate (PbTiO). Short-range order structure was revealed using atomic pair-distribution function (PDF) method. In the high-temperature cubic phase, there is a large deviation between local and average structure. Especially, Pb atoms deviated from the cubic lattice framework, but establish Pb-O-Pb random network.

Synthesis of hexagonal boron carbonitride without nitrogen void defects

Mannan, M. A.*; Baba, Yuji; Kida, Tetsuya*; Nagano, Masamitsu*; Noguchi, Hideyuki*

Materials Sciences and Applications, 6(5), p.353 - 359, 2015/05

https://doi.org/10.4236/msa.2015.65041

The synthesis and structure of hexagonal boron carbonitride (h-BCN) film on polycrystalline diamond surface were reported. Polycrystalline diamond and/or diamond-like carbon were first fabricated on Si (100) and then it was used as substrate. The deposition was performed by radio frequency plasma enhanced chemical vapor deposition. In order to reduce the content of nitrogen void defects, the deposition was performed at the high temperature of 950C under the working pressure of 2.6 Pa. The typical sample with atomic composition of BCNO in the h-BCN lattice was characterized by X-ray photoelectron spectroscopy. The fine structure of the film was studied by near-edge X-ray absorption fine structure (NEXAFS) measurements. The B K-edge and N K-edge of NEXAFS spectra revealed that the synthesized h-BCN film has the ideal honeycomb-like BN configuration without nitrogen void defects.

Conceptual design of small-sized HTGR system, 4; Plant design and technical feasibility

Ohashi, Hirofumi; Sato, Hiroyuki; Yan, X.; Sumita, Junya; Nomoto, Yasunobu; Tazawa, Yujiro; Noguchi, Hiroki; Imai, Yoshiyuki; Tachibana, Yukio

JAEA-Technology 2013-016, 176 Pages, 2013/09

JAEA-Technology-2013-016.pdf:8.62MB

JAEA has started a conceptual design of a 50MWt small-sized high temperature gas cooled reactor for steam supply and electricity generation (HTR50S), which is a first-of-kind of the commercial plant or a demonstration plant of a small-sized HTGR system for steam supply to the industries and district heating and electricity generation by a steam turbine. The plant design of HTR50S for the steam supply and electricity generation was performed based on the plant specification and the requirements for each system taking into account for the increase of the reactor outlet coolant temperature from 750C to 900C and the installation of IHX. The technical feasibility of HTR50S was confirmed because the designed systems satisfies the design requirements. The conceptual plant layout was also determined. This paper provides the summary of the plan design and technical feasibility of HTR50S.

Damped soft phonons and diffuse scattering in (BiNa)TiO

Matsuura, Masato*; Iida, Hiroyuki*; Hirota, Kazuma*; Owada, Kenji; Noguchi, Yuji*; Miyayama, Masaru*

Physical Review B, 87(6), p.064109_1 - 064109_10, 2013/02

https://doi.org/10.1103/PhysRevB.87.064109

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.

Electronic and local structures of Mn-doped BiFeO crystals

Yoneda, Yasuhiro; Kitanaka, Yuki*; Noguchi, Yuji*; Miyayama, Masaru*

Physical Review B, 86(18), p.184112_1 - 184112_11, 2012/11

https://doi.org/10.1103/PhysRevB.86.184112

The electronic structure of complex oxides is important for understanding their functional properties. Here we report the results of investigating multiferroic BiFeO using various X-ray spectroscopy techniques. Zn- and Mn-codoped and Mn-doped BiFeO samples were prepared with the aim of improving ferroelectric properties of BiFeO. The valences of the doped Mn and host Fe were investigated. When oxygen vacancies exist in the sample, Mn acts as a hole acceptor. Furthermore, Mn and Fe stabilize the perovskite unit by changing their ionic radius. As a result, Mn and Fe atoms exhibit various valence states in the BiFeO system. Evidence of the electronic structure for Fe -O -Bi hybridization is also presented.