Structural behaviors of lead zirconate titanate-based ferroelectric ceramics during pyroelectric-power generation cycles

Kawasaki, Takuro; Fukuda, Tatsuo; Yamanaka, Satoru*; Murayama, Ichiro*; Kato, Takanori*; Baba, Masaaki*; Hashimoto, Hideki*; Harjo, S.; Aizawa, Kazuya; Tanaka, Hirohisa*; et al.

Journal of Applied Physics, 137(9), p.094101_1 - 094101_7, 2025/03

https://doi.org/10.1063/5.0243081

Magnetoelastic coupling for Fe-Ga thin films epitaxially grown on different substrates

Ding, H.*; Ito, Keita*; Endo, Yasushi*; Takanashi, Koki; Seki, Takeshi*

Journal of Physics D; Applied Physics, 57(38), p.385002_1 - 385002_10, 2024/09

https://doi.org/10.1088/1361-6463/ad58f0

An Experimental feasibility study of a 4 gamma-ray imager using detector response patterns

Kitayama, Yoshiharu; Nogami, Mitsuhiro*; Hitomi, Keitaro*

Japanese Journal of Applied Physics, 63(7), p.076502_1 - 076502_8, 2024/07

https://doi.org/10.35848/1347-4065/ad5ba0

We constructed a gamma-ray imager that estimates the distribution of gamma-ray sources based on the response patterns of multiple gamma-ray detectors randomly positioned in three-dimensional space. The Coded Cube Camera for Gamma-ray (C3G), comprising eight GAGG (Ce) scintillator and eighteen lead cubes is housed in a cubical casing with an 86 mm edge length and weighs approximately 600 g. Results of the 4 imaging experiment confirmed the feasibility of imaging a 10 MBq Cs source located 3 m away with an angular uncertainty of 5 within a 10 min measurement. C3G operates with only eight channels, instead of the hundreds needed by a typical imager, offering a simplified circuit and reconstruction algorithm, thereby achieving a cost-effective and reliable system. With its compact and lightweight design, 4 field of view, and high angular uncertainty, this technology is expected to find extensive applications in astronomy, medicine, nuclear security, and decommissioning projects.

Giant barocaloric effects in sodium hexafluorophosphate and hexafluoroarsenate

Zhang, Z.*; Hattori, Takanori; Song, R.*; Yu, D.*; Mole, R.*; Chen, J.*; He, L.*; Zhang, Z.*; Li, B.*

Journal of Applied Physics, 136(3), p.035105_1 - 035105_8, 2024/07

https://doi.org/10.1063/5.0211085

Solid-state refrigeration using barocaloric materials is environmentally friendly and highly efficient, making it a subject of global interest over the past decade. Here, we report giant barocaloric effects in sodium hexafluorophosphate (NaPF) and sodium hexafluoroarsenate (NaAsF) that both undergo a cubic-to-rhombohedral phase transition near room temperature. We have determined that the low-temperature phase structure of NaPF is a rhombohedral structure with space group R and NaAsF, i.e., F, E, and A. The phase transition temperature varies with pressure at a rate of dT/dP = 250 and 310 K/GPa for NaPF and NaAsF. The pressure-induced entropy changes of NaPF and NaAsF are determined to be around 45.2 and 35.6J kgK, respectively. The saturation driving pressure is about 40 MPa. The pressure-dependent neutron powder diffraction suggests that the barocaloric effects are related to the pressure-induced cubic-to-rhombohedral phase transitions.

Evaluation of quenching characteristics of Li-containing scintillators

Watanabe, Kenichi*; Oshima, Yuya*; Shigyo, Nobuhiro*; Hirata, Yuho

Japanese Journal of Applied Physics, 63(5), p.056001_1 - 056001_5, 2024/05

https://doi.org/10.35848/1347-4065/ad39bd

Lithium-containing scintillators are used for neutron detection; Li-containing scintillators detect tritons and alpha rays produced by neutrons. Since these particles deposit higher energy than gamma rays, Li-containing scintillators can separate gamma rays and neutrons. However, the luminescence efficiency of scintillator decreases for ion beams due to a phenomenon called the quenching effect. Evaluation of the quenching effect is necessary to accurately separate neutrons and gamma rays. The Birks equation is used to predict the scintillation efficiency change due to the quenching effect, but it is necessary to determine the quenching coefficient in the Birks equation. In this study, we used PHITS to calculate the luminescence of Li-containing scintillators considering the quenching effect based on Birks' equation with the quenching coefficient as a free parameter. Then, by comparing the simulated results with the experimentally obtained luminescence, the extinction coefficients of Li glass, Ce:LiCaAlF, and Eu:LiCaAlF scintillators were determined.

Simulation of a gamma-ray imaging technique using detector response patterns

Kitayama, Yoshiharu; Nogami, Mitsuhiro*; Hitomi, Keitaro*

Japanese Journal of Applied Physics, 63(3), p.032005_1 - 032005_6, 2024/03

https://doi.org/10.35848/1347-4065/ad2d7a

We introduce a novel gamma-ray imaging technique that uses detector response patterns. This method employs multiple shielding cubes randomly positioned in a three-dimensional configuration. Within the volume defined by these cubes, a unique gamma-ray flux pattern is formed based on the incidence direction of the gamma rays. This pattern can be measured using the responses of several scintillator cubes. By pre-measuring the detector response pattern and incidence direction of the gamma rays, the incidence direction can be estimated using an unfolding technique. Simulations were performed using a Cs point source. Our results show that a 10 MBq Cs source, located 3 m away from the imager, can be imaged with an angular resolution close to 10. These findings suggest that our new method is comparable to existing gamma-ray imaging techniques. Potential applications of this imaging method include nuclear power plant decommissioning, nuclear medicine, security, and astronomy.

Local structure analysis of BiNaTiOBaTiO solid solutions

Yoneda, Yasuhiro; Kobayashi, Toru; Tsuji, Takuya; Matsumura, Daiju; Saito, Yuji; Noguchi, Yuji*

Japanese Journal of Applied Physics, 62(SM), p.SM1006_1 - SM1006_8, 2023/11

https://doi.org/10.35848/1347-4065/ace3cd

BiNaTiOBaTiO (BNTBT) solid solutions have been extensively studied because they exhibit good piezoelectric properties. In addition, a wide variety of phases are observed depending on the BT composition. Soft X-ray absorption spectroscopy and high-energy X-ray diffraction experiments of BNTBT solid solutions were performed using synchrotron radiation. From the electronic structure and local structure of BNTBT solid solution, the substitution effect of BT occurred mainly at the A site, which is the substitution site of Ba. The rhombohedral strain of the TiO octahedron did not change with the change in BT composition, suggesting that the change in the electronic structure at the O- absorption edge is due to the change in the hybridization state.

A Novel method for processing noisy magnetotelluric data based on independence of signal sources and continuity of response functions

Ogawa, Hiroki; Asamori, Koichi; Negi, Tateyuki*; Ueda, Takumi*

Journal of Applied Geophysics, 213, p.105012_1 - 105012_17, 2023/06

https://doi.org/10.1016/j.jappgeo.2023.105012

A number of schemes for processing magnetotelluric (MT) data have been reported aiming at suppressing the strong effect of artificial electromagnetic noise, especially coherent noise that is correlated between electric and magnetic time series. Many of the recent denoising schemes are based on decomposing MT data into the responses of the natural signal and noise. Meanwhile, it is crucial to distinguish the natural signal from noise stably without depending on any empirical choice of parameter setting. In addition, improper subtraction of values from the separated signal can lead to the loss of useful values of the natural signal or missing noise-affected values, which may result in failure in deriving the true MT responses. We propose a novel data-processing method that applies frequency-domain independent component analysis (FDICA) to both the local MT data and the reference magnetic data. Among the separated signal, the proposed method can quantitatively distinguish the natural signal from the noise-affected components by calculating the ratio of cross-power spectrum with the reference data to the auto-power spectrum for each component. When determining which values to subtract from the separated signal, we introduce an evaluation index with respect to two characteristics of the MT response function: stationary in the time domain and smoothness in the frequency domain. We conduct the experiments both with MT time series severely contaminated by synthetic coherent noises and with MT field data interfered with DC (direct current) railways. Consequently, we confirm the superiority of the proposed method in the noise-suppression performance over the conventional methods of MT data processing.

Spin and spin current; From fundamentals to recent progress

Maekawa, Sadamichi; Kikkawa, Takashi*; Chudo, Hiroyuki; Ieda, Junichi; Saito, Eiji

Journal of Applied Physics, 133(2), p.020902_1 - 020902_24, 2023/01

https://doi.org/10.1063/5.0133335

Local structure analysis of BiFeO-BaTiO solid solutions

Yoneda, Yasuhiro; Kim, S.*; Mori, Shigeo*; Wada, Satoshi*

Japanese Journal of Applied Physics, 61(SN), p.SN1022_1 - SN1022_10, 2022/11

https://doi.org/10.35848/1347-4065/ac835d

Local structural analysis of the (1-) BiFeO-BaTiO solid solution was performed by PDF analysis of the data obtained in the synchrotron radiation high-energy X-ray diffraction experiment. First, when XAFS experiments were performed and sample screening was performed, it was found that structural fluctuations were large in the BiFeO-rich composition. Therefore, PDF analysis of a sample with BiFeO-rich composition was performed. As a result, it was found that although the average structure is a cubic structure, the local structure can be reproduced with a rhombohedral crystal structure, and there is a displacement that breaks the symmetry of the rhombohedral structure in a composition with a large fluctuation.