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-BaTiO solid solutionsYoneda, Yasuhiro; Kim, S.*; Mori, Shigeo*; Wada, Satoshi*
Japanese Journal of Applied Physics, 61(SN), p.SN1022_1 - SN1022_10, 2022/11
Times Cited Count：1 Percentile：15.88(Physics, Applied)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.
nanocrystalsYoneda, 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：4 Percentile：21.5(Physics, Applied) nanocrystals with cubic shapeYoneda, 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 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.
nanocubes by solvothermal synthesisYoneda, Yasuhiro; Kohara, Shinji*; Nakashima, Koichi*; Nagata, Hajime*; Wada, Satoshi*
Japanese Journal of Applied Physics, 54(10S), p.10NC01_1 - 10NC01_6, 2015/10
Times Cited Count：4 Percentile：18.5(Physics, Applied)The atomic-scale structure of KNbO nanopowder synthesized by solvothermal method has been studied using high-energy X-ray diffraction, Rietveld refinement, and the atomic pair-distribution function (PDF) technique. It was found that the local structure of KNbO nanoparticles deviates from the average structure. The local structure was found to be rhombohedral structure though the average structure was tetragonal structure. The rhombohedral distortion of NbO
octahedra was maintained in the annealed sample.
and KNbO solid solutionYoneda, Yasuhiro; Kohara, Shinji*; Kumada, Nobuhiro*; Wada, Satoshi*
Japanese Journal of Applied Physics, 53(9S), p.09PD01_1 - 09PD01_5, 2014/09
Times Cited Count：3 Percentile：13.34(Physics, Applied)The atomic-scale structure of solid solution of BaTiO (BT) and KNbO (KN) has been studied using high-energy X-ray diffraction, X-ray absorption fine structure, and atomic pair-distribution function analysis techniques. We prepared BT-KN solid solution through KNbTiO
, in which Ti and Nb atoms are arranged randomly. The average structure of BT-KN solid solution was cubic structure and the local strcuture is also reproduced by the cubic structure. It is rare that a solid solution synthesized from ferroelectric materials has a local strcuture of a paraelectric material. Since the original correlation of BT or KN was lost, ferroelectricity disappeared in the BT-KN solid solution.
Yoneda, Yasuhiro; Kobune, Masafumi*; Wada, Satoshi*; Fu, D.*
no journal, ,
NaNbO shows a complex phase transition sequence. The average structure transformed from an orthorhombic to rhombohedral structure at the phase transition temperature. This phase transition has been found to be diffuse and the orthorhombic and rhombohedral phases coexist at wide temperature ranges. The origin of the diffuse phase transition should be the randomness of the local structure. We performed atomic-pair distribution function analysis by using NaNbO samples grown by various synthesis method to clarify the relationship between the local structure and the phase transition. We demonstrated that the off-center shift of Nb atoms from the center on NbO ocrahedra coupled with the rhombohedral to orthorhombic phase transition.
nanocrystalsYoneda, Yasuhiro; Kunisada, Ryoichi*; Chikada, Tsukasa*; Ueno, Shintaro*; Fujii, Ichiro*; Wada, Satoshi*
no journal, ,
High-energy X-ray diffraction measurements were performed to analyze KNbO nanocrystals. We used KNbO nanocrystals with cubic shape. Moreover, these nanocrystals have cubic structure owing to their small crystal size. Therefore, these nanocrystals are ideal for applying the Scherrer's equation. Crystal-growth mechanism was considered with the crystal size obtained by the Scherrer's equation. It was found the growth mechanism of KNbO by comparing the crystal size and average structure obtained by Rietveld analysis and coherent size obtained by atomic pair-distribution function method.
nano crystalsYoneda, Yasuhiro; Kunisada, Ryoichi*; Ueno, Shintaro*; Fujii, Ichiro*; Wada, Satoshi*
no journal, ,
The high-energy X-ray diffraction experiments of KNbO nanocrystals were carried out. Although Scherrer's equation may be used in estimating the particle diameters, in practical use there are various restrictions. In this study, we used KNbO nanocrystals synthesized by a solvothermal method with a cubic shape. The crystal structure were a cubic structure because of the small particle size, it can be said that the KNbO sample is an ideal to apply the Scherrer's equation. The crystal growth proceeds with the reaction time was investigated the kinetics of crystal growth. The short-range order structure was also observed, which was directly determined in the real space from the atomic pair-distribution distribution function method. It was found that the initial growth of KNbO nano crystal was suppressed because of lattice defects.
-Bi(Mg,Ti)O mixtureYoneda, Yasuhiro; Wada, Satoshi*
no journal, ,
BiFeO is a useful ferroelectric material, but it is not easy to reverse the polarization because the rhombohedral structure of the ferroelectric phase is greatly distorted, and attempts have been made to improve the dielectric properties by various additives. BaTiO and Bi(Mg
Ti)O were selected as additives, and structural analysis was performed using synchrotron radiation. BiFeO has a rhombohedral structure and BaTiO has a tetragonal structure. Bi(MgTi)O has an antiferroelectric orthorhombic structure and is expected to behave as a buffer that binds BiFeO and BaTiO. The process of averaging the structure from micro to macro was clarified, and various changes were observed depending on the temperature. The flexibility of such a structure reduces the large distortion of BiFeO
and enables polarization.
-BaTiO solid solutionYoneda, Yasuhiro; Kim, S.*; Wada, Satoshi*
no journal, ,
In a solid solution formed with BiFeO and BaTiO, a pseudo cubic phase appears at room temperature with a BaTiO composition of 0.3 to 0.7. Since the ferroelectricity is not lost even in the Cubic structure, a structural analysis using pair distribution function was performed to clarify the origin of the ferroelectricity. The local structure of these solid solutions was consistent with the pure limits of BiFeO and BaTiO, respectively, but when the BaTiO composition was 0.3, a structure peculiar to the solid solution appeared.
Yoneda, Yasuhiro; Nam, H.*; Ueno, Shintaro*; Fujii, Ichiro*; Kim, S.*; Wada, Satoshi*
no journal, ,
