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Journal Articles

Nanoscale structural analysis of Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ in high-temperature phases

Yoneda, Yasuhiro; Noguchi, Yuji*

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

 Times Cited Count:0 Percentile:0(Physics, Applied)

Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ (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 400$$^{circ}$$C. 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 200$$^{circ}$$C, and this shift becomes an order parameter for the phase transition.

Journal Articles

Pairing forces govern population of doubly magic $$^{54}$$Ca from direct reactions

Browne, F.*; Chen, S.*; Doornenbal, P.*; Obertelli, A.*; Ogata, Kazuyuki*; Utsuno, Yutaka; Yoshida, Kazuki; Achouri, N. L.*; Baba, Hidetada*; Calvet, D.*; et al.

Physical Review Letters, 126(25), p.252501_1 - 252501_7, 2021/06

 Times Cited Count:0 Percentile:0.01(Physics, Multidisciplinary)

Direct proton-knockout reactions of $$^{55}$$Sc were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of $$^{54}$$Ca were investigated through $$gamma$$-ray and invariant-mass spectroscopy. Level energies were calculated from the nuclear shell model employing a phenomenological inter-nucleon interaction. Theoretical cross sections to states were calculated from distorted-wave impulse approximation estimates multiplied by the shell model spectroscopic factors. Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of $$^{55}$$Sc, valence proton removals populated predominantly the ground-state of $$^{54}$$Ca. This counter-intuitive result is attributed to pairing effects leading to a dominance of the ground-state spectroscopic factor. Owing to the ubiquity of the pairing interaction, this argument should be generally applicable to direct knockout reactions from odd-even to even-even nuclei.

Journal Articles

First spectroscopic study of $$^{51}$$Ar by the ($$p$$,2$$p$$) reaction

Juh$'a$sz, M. M.*; Elekes, Z.*; Sohler, D.*; Utsuno, Yutaka; Yoshida, Kazuki; Otsuka, Takaharu*; Ogata, Kazuyuki*; Doornenbal, P.*; Obertelli, A.*; Baba, Hidetada*; et al.

Physics Letters B, 814, p.136108_1 - 136108_8, 2021/03

 Times Cited Count:1 Percentile:79.03(Astronomy & Astrophysics)

The nuclear structure of $$^{51}$$Ar was studied by the ($$p$$,2$$p$$) reaction using $$gamma$$-ray spectroscopy for the bound and unbound states. Comparing the results to our shell-model calculations, two bound and six unbound states were established. The low cross sections populating the two bound states of $$^{51}$$Ar could be interpreted as a clear signature for the presence of significant sub-shell closures at neutron numbers 32 and 34 in argon isotopes.

Journal Articles

Quasifree neutron knockout reaction reveals a small $$s$$-Orbital component in the Borromean nucleus $$^{17}$$B

Yang, Z. H.*; Kubota, Yuki*; Corsi, A.*; Yoshida, Kazuki; Sun, X.-X.*; Li, J. G.*; Kimura, Masaaki*; Michel, N.*; Ogata, Kazuyuki*; Yuan, C. X.*; et al.

Physical Review Letters, 126(8), p.082501_1 - 082501_8, 2021/02

 Times Cited Count:8 Percentile:97.59(Physics, Multidisciplinary)

A quasifree ($$p$$,$$pn$$) experiment was performed to study the structure of the Borromean nucleus $$^{17}$$B, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for $$1s_{1/2}$$ and $$0d_{5/2}$$ orbitals, and a surprisingly small percentage of 9(2)% was determined for $$1s_{1/2}$$. Our finding of such a small $$1s_{1/2}$$ component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in $$^{17}$$B. The present work gives the smallest $$s$$- or $$p$$-orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of $$s$$ or $$p$$ orbitals is not a prerequisite for the occurrence of a neutron halo.

Journal Articles

$$N$$ = 32 shell closure below calcium; Low-lying structure of $$^{50}$$Ar

Cort$'e$s, M. L.*; Rodriguez, W.*; Doornenbal, P.*; Obertelli, A.*; Holt, J. D.*; Men$'e$ndez, J.*; Ogata, Kazuyuki*; Schwenk, A.*; Shimizu, Noritaka*; Simonis, J.*; et al.

Physical Review C, 102(6), p.064320_1 - 064320_9, 2020/12

 Times Cited Count:1 Percentile:38.19(Physics, Nuclear)

Low-lying excited states in the $$N$$ = 32 isotope $$^{50}$$Ar were investigated by in-beam $$gamma$$-ray spectroscopy following proton- and neutron-knockout, multinucleon removal, and proton inelastic scattering at the RIKEN Radioactive Isotope Beam Factory. The energies of the two previously reported transitions have been confirmed, and five additional states are presented for the first time, including a candidate for a 3$$^{-}$$ state. The level scheme built using $$gamma$$ $$gamma$$ coincidences was compared to shell-model calculations in the $$sd-pf$$ model space and to ${it ab initio}$ predictions based on chiral two- and three-nucleon interactions. Theoretical proton- and neutron-knockout cross sections suggest that two of the new transitions correspond to 2$$^{+}$$ states, while the previously proposed 4$$^{+}_{1}$$ state could also correspond to a 2$$^{+}$$ state.

Journal Articles

Nanoscale structural analysis of Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$

Yoneda, Yasuhiro; Noguchi, Yuji*

Japanese Journal of Applied Physics, 59(SP), p.SPPA01_1 - SPPA01_7, 2020/11

 Times Cited Count:7 Percentile:82.73(Physics, Applied)

We investigate A-site cation ordering in the ferroelectric perovskite Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ (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.

Journal Articles

Shell evolution of $$N$$ = 40 isotones towards $$^{60}$$Ca; First spectroscopy of $$^{62}$$Ti

Cort$'e$s, M. L.*; Rodriguez, W.*; Doornenbal, P.*; Obertelli, A.*; Holt, J. D.*; Lenzi, S. M.*; Men$'e$ndez, J.*; Nowacki, F.*; Ogata, Kazuyuki*; Poves, A.*; et al.

Physics Letters B, 800, p.135071_1 - 135071_7, 2020/01

 Times Cited Count:12 Percentile:96.98(Astronomy & Astrophysics)

Excited states in the $$N$$ = 40 isotone $$^{62}$$Ti were populated via the $$^{63}$$V($$p$$,$$2p$$)$$^{62}$$Ti reaction at $$sim$$200 MeV/nucleon at the Radioactive Isotope Beam Factory and studied using $$gamma$$-ray spectroscopy. The energies of the $$2_1^+ rightarrow 0_{rm gs}^+$$ and $$4_1^+ rightarrow 2_1^+$$ transitions, observed here for the first time, indicate a deformed Ti ground state. These energies are increased compared to the neighboring $$^{64}$$Cr and $$^{66}$$Fe isotones, suggesting a small decrease of quadrupole collectivity. The present measurement is well reproduced by large-scale shell-model calculations based on effective interactions, while ab initio and beyond mean-field calculations do not yet reproduce our findings.

Journal Articles

Synchrotron radiation-based techniques available at JAEA advanced characterization nanotechnology platform (Japan Atomic Energy Agency)

Yoneda, Yasuhiro; Yoshigoe, Akitaka; Takeda, Yukiharu; Shiwaku, Hideaki; Matsumura, Daiju; Shobu, Takahisa; Tamura, Kazuhisa

Materia, 58(12), p.763 - 769, 2019/12

This is an introduction to the equipment provided for each implementation period belonging to the structure analysis platform in the nanotechnology platform.

Journal Articles

Short- and middle-ranges order structures of KNbO$$_3$$ nanocrystals

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

 Times Cited Count:2 Percentile:23.94(Physics, Applied)

Journal Articles

Synthesis of new perovskite-type oxyfluorides, BaInO$$_{2}$$F and comparison of the structure among perovskite-type oxyfluorides

Katsumata, Tetsuhiro*; Suzuki, Ryo*; Sato, Naoto*; Suzuki, Shumpei*; Nakashima, Mamoru*; Inaguma, Yoshiyuki*; Mori, Daisuke*; Aimi, Akihisa*; Yoneda, Yasuhiro

Journal of Solid State Chemistry, 279, p.120919_1 - 120919_8, 2019/11

 Times Cited Count:5 Percentile:48.48(Chemistry, Inorganic & Nuclear)

Journal Articles

Quasifree neutron knockout from $$^{54}$$Ca corroborates arising $$N=34$$ neutron magic number

Chen, S.*; Lee, J.*; Doornenbal, P.*; Obertelli, A.*; Barbieri, C.*; Chazono, Yoshiki*; Navr$'a$til, P.*; Ogata, Kazuyuki*; Otsuka, Takaharu*; Raimondi, F.*; et al.

Physical Review Letters, 123(14), p.142501_1 - 142501_7, 2019/10

 Times Cited Count:21 Percentile:92.66(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Relation between the structure and tolerance factor for perovskite-type oxyfluorides

Katsumata, Tetsuhiro*; Inaguma, Nobuyuki*; Mori, Daisuke*; Aimi, Akihisa*; Yoneda, Yasuhiro

Seramikkusu, 54(9), p.629 - 632, 2019/09

Crystal structure analysis of ABO$$_3$$ perovskite-type oxyfluoride were performed by using high-energy synchrotron X-ray measurement. The effect of tolerance factor appeared in the local structure. The average structure of perovskite-type oxyfluoride found to be a cubic structure in the traditional crystal structure analysis.

Journal Articles

Local structure analysis of PbTiO$$_3$$ in high-temperature cubic phase

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

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

 Times Cited Count:3 Percentile:33.49(Materials Science, Multidisciplinary)

High-energy X-ray diffraction study was performed on lead titanate (PbTiO$$_3$$). 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.

Journal Articles

Observation of simulated fuel debris using synchrotron radiation

Yoneda, Yasuhiro; Harada, Makoto; Takano, Masahide

Transactions of the Materials Research Society of Japan, 44(2), p.61 - 64, 2019/04

We performed three-dimensional observation of simulated fuel debris using Synchrotron Computed Tomography (CT). CT was used to make the inside of fuel debris clear. The CT observation provides that a clear contrast in the zirconia rich part and concrete rich part. Zirconia heavier than concrete moved to the lower part when crystals precipitate and aggregates near the bottom surface. As a result, phase separation occurs. The phase separation is caused by the difference in the composition ratio of zirconia, and can also be observed difference in crystal growth mode by composition ratio.

Journal Articles

Local structure study of the iron-based systems of BaFe$$_2$$As$$_2$$ and LiFeAs by X-ray PDF and XAFS analyses

Li, S.*; Toyoda, Masayuki*; Kobayashi, Yoshiaki*; Ito, Masayuki*; Ikeuchi, Kazuhiko*; Yoneda, Yasuhiro; Otani, Akira*; Matsumura, Daiju; Asano, Shun*; Mizuki, Junichiro*; et al.

Physica C, 555, p.45 - 53, 2018/12

 Times Cited Count:1 Percentile:8.47(Physics, Applied)

${it T}$-dependence of local distortions in BaFe$$_2$$As$$_2$$ and LiFeAs by X-ray PDF and XAFS methods. Although PDF data exhibit anomaly at the structure transition temperature, EXAFS data exhibit no anomaly. Data supporting the local orthorhombicity at 300 K in the tetragonal phase for BaFe$$_2$$As$$_2$$. Arguments on the origins of the 4-fold symmetry breaking in the ground average structure of the tetragonal phase.

Journal Articles

Local structure and phase transitions of KNbO$$_3$$

Yoneda, Yasuhiro; Ohara, Koji*; Nagata, Hajime*

Japanese Journal of Applied Physics, 57(11S), p.11UB07_1 - 11UB07_6, 2018/11

 Times Cited Count:9 Percentile:56.55(Physics, Applied)

Local structure analysis of KNbO$$_3$$, 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.

Journal Articles

Local structure analysis of KNbO$$_3$$ nanocrystals with cubic shape

Yoneda, Yasuhiro; Kunisada, Ryoichi*; Chikada, Tsukasa*; Ueno, Shintaro*; Ohara, Koji*; Wada, Satoshi*

Transactions of the Materials Research Society of Japan, 43(2), p.93 - 96, 2018/04

KNbO$$_3$$ nanocrystals were grown by solvothermal technique assisted by a microwave treatment. We performed high-energy X-ray diffraction to extract average and local structural parameters. The particle size can be evaluated by the Scherrer's equation. The unit cell size was reduced as the particle size increased. The local structure was found to be a rhombohedral structure, which was similar to that of the bulk KNbO$$_3$$.

Journal Articles

Raman scattering study of the ferroelectric phase transition in BaTi$$_2$$O$$_5$$

Tsukada, Shinya*; Fujii, Yasuhiro*; Yoneda, Yasuhiro; Moriwake, Hiroki*; Konishi, Ayako*; Akishige, Yukikuni*

Physical Review B, 97(2), p.024116_1 - 024116_7, 2018/02

 Times Cited Count:14 Percentile:74.54(Materials Science, Multidisciplinary)

Uniaxial ferroelectric BaTi$$_2$$O$$_5$$ with a Curie temperature $$T_{rm C}$$ of 743 K was investigated to clarify its paraelectric-ferroelectric phase transition behavior. The mechanism is discussed on the basis of the structure from short to long ranges determined by synchrotron X-ray diffraction and the lattice dynamics probed by Raman spectroscopy. Using a combination of experimental results and first-principles calculations, we explain the phase transition. Ti vibration of TiO$$_6$$ octahedral units is frozen in the ferroelectric phase and the space group changes from nonpolar $$C2/m$$ to polar $$C2$$.

Journal Articles

Local structure analysis of (Na$$_{0.5}$$K$$_{0.45}$$Li$$_{0.05}$$)NbO$$_3$$ synthesized by malic acid complex solution method

Yoneda, Yasuhiro; Takada, Eri*; Nagai, Haruka*; Kikuchi, Takeyuki*; Morishita, Masao*; Kobune, Masafumi*

Japanese Journal of Applied Physics, 56(10S), p.10PB07_1 - 10PB07_7, 2017/10

 Times Cited Count:3 Percentile:21.75(Physics, Applied)

A monoclinic phase was discovered in (Na$$_{0.5}$$K$$_{0.45}$$Li$$_{0.05}$$)NbO$$_3$$ solid solution ceramics grown by a malic acid complex solution method. The average and local structures of this monoclinic phase were analyzed by synchrotron X-ray measurements. The local structure can be reproduced by assuming a rhombohedral model, that is the same local structure of KNbO$$_3$$. The results demonstrate that the monoclinic average structure is observed as a disordered rhombohedral structure.

Journal Articles

Local structure analysis of relaxor Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$

Yoneda, Yasuhiro; Taniguchi, Hiroki*; Fu, D.*

Ferroelectrics, 513(1), p.1 - 6, 2017/09

 Times Cited Count:6 Percentile:41.6(Materials Science, Multidisciplinary)

An EXAFS study of lead magnesium niobate was performed at the Nb K edge and at the Pb L3 edge at 300 K. Two Nb-O bond lengths of 1.91 and 2.10${AA}$ are observed and there is no significant modification of the local environment of the Nb atoms compared with NaNbO$$_3$$ and AgNbO$$_3$$. The weak Pb L3 EXAFS signal indicated a strong static disorder, which can be extracted by PDF analysis.

199 (Records 1-20 displayed on this page)