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Journal Articles

Crystallographical and morphological changes in charge-ordering transition of RFe $_{2}$ O $_{4}$ (R: Y, Lu) investigated by transmission electron microscopy

Horibe, Yoichi*; Mori, Shigeo*; Ikeda, Naoshi*; Yoshii, Kenji; Maeno, Hiroshi*; Murakami, Yasukazu*

Ferroelectrics, 584(1), p.20 - 30, 2021/00

https://doi.org/10.1080/00150193.2021.1984762

Times Cited Count：1 Percentile：7.92(Materials Science, Multidisciplinary)

Temperature dependence of charge-ordered crystal structures and domain structures in RFe $_{2}$ O $_{4}$ (R: Y and Lu) was investigated by energy-filtered transmission electron microscopy, combined with conventional transmission electron microscopy. The presence of three-dimensional to two-dimensional charge ordering transition were observed in both RFe $_{2}$ O $_{4}$ on heating. Furthermore, real-space images obtained with the energy-filtered transmission electron microscopy revealed that YRFe $_{2}$ O $_{4}$ has less anisotropic nanometer-scale charge-ordered domains than LuRFe $_{2}$ O $_{4}$ . These findings in RFe $_{2}$ O $_{4}$ indicate the importance of the interchange interactions between Fe-O bilayers in addition to those within bilayers in the structural phase transitions associated with charge ordering in this system.

Journal Articles

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

Times Cited Count：5 Percentile：27.39(Materials Science, Multidisciplinary)

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.

Journal Articles

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

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

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

https://doi.org/10.1080/00150193.2017.1350050

Times Cited Count：7 Percentile：35.49(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 are observed and there is no significant modification of the local environment of the Nb atoms compared with NaNbO and AgNbO. The weak Pb L3 EXAFS signal indicated a strong static disorder, which can be extracted by PDF analysis.

Journal Articles

Pyroelectric power generation with ferroelectrics (1-x)PMN-xPT

Kim, J.*; Yamanaka, Satoru*; Nakajima, Akira*; Kato, Takanori*; Kim, Y.*; Fukuda, Tatsuo; Yoshii, Kenji; Nishihata, Yasuo; Baba, Masaaki*; Takeda, Masatoshi*; et al.

Ferroelectrics, 512(1), p.92 - 99, 2017/08

https://doi.org/10.1080/00150193.2017.1349991

Times Cited Count：14 Percentile：56.08(Materials Science, Multidisciplinary)

Journal Articles

Local structure analysis of TiO $_{3}$ ( = Sr, Ba, Pb)

Yoneda, Yasuhiro; Kohara, Shinji*

Ferroelectrics, 485(1), p.34 - 41, 2015/00

https://doi.org/10.1080/00150193.2015.1060095

Times Cited Count：3 Percentile：14.69(Materials Science, Multidisciplinary)

High-energy X-ray total scattering provides simultaneous information about long-range order through the Bragg peaks and short-range order through the diffuse scattering. In ferroelectric materials, short-range order structure inside the ferroelectric domains tends to deviate from the average structure. The local structure analysis is necessary to reveal the ferroelectric mechanism. We applied atomic pair-distribution function (PDF) analysis using synchrotron X-ray for the study of local structure of ferroelectrics having perovskite structure. In BaTiO, since local distortion is averaged out owing to the requirements of periodicity and harmonic lattice vibrations, the average structure showed a cubic structure. The actual structure of systems which displays so much instability and disorder can be revealed by the PDF analysis.

Journal Articles

Multiferroic character and magnetic phase of LuFe $_{2}$ O $_{4}$

Oishi, Daisuke*; Hayakawa, Hironori*; Akahama, Hiroshi*; Ikeda, Naoshi*; Kambe, Takashi*; Matsuo, Yoji*; Kimizuka, Noboru*; Kano, Jun*; Yoshii, Kenji

Ferroelectrics, 415(1), p.51 - 56, 2011/10

https://doi.org/10.1080/00150193.2011.577371

Times Cited Count：5 Percentile：25.35(Materials Science, Multidisciplinary)

The variation of AC dielectric constant in the function of the DC magnetic fields was found in low oxygen vacant LuFe $_{2}$ O $_{4}$ single crystal in which the electric polarization arise from the polar charge ordering. These magneto-electric coupling should be explained by a novel mechanism where the boundary motion of the polar charge ordered domain is affected by the magnetic (spin) domain boundary motion.

Journal Articles

Mathematical model of domain formation in barium titanate

Yoneda, Yasuhiro

Ferroelectrics, 414(1), p.86 - 89, 2011/06

https://doi.org/10.1080/00150193.2011.577311

Times Cited Count：0 Percentile：0(Materials Science, Multidisciplinary)

The numerical model of the ferroelectric domain formation has been described with the polarization network, because it has been understood that a long-range network of elastic strain is generated by the inhomogeneity of polarization. Recently, the direct observation of long-range elastic strain has been able to be performed by several methods. We made an attempt to construct a mathematical model of the domain formation in BaTiO using elastic strain as a parameter.

Journal Articles

Nanometer-sized domain structures in LuFeO $_{4}$ (=Cu, Co) revealed by energy-filtered transmission electron microscopy

Matsuo, Yoji*; Hirata, Akihiko*; Horibe, Yoichi*; Yoshii, Kenji; Ikeda, Naoshi*; Mori, Shigeo*

Ferroelectrics, 380(1), p.56 - 62, 2009/06

https://doi.org/10.1080/00150190902873204

Times Cited Count：6 Percentile：29.51(Materials Science, Multidisciplinary)

Diluted effect on the charge ordered (CO) structure in dielectric materials LuFeO $_{4}$ (=Cu, Co) were investigated by an energy-filtered transmission electron microscope (TEM), in combination with a conventional TEM. It is revealed that partial substitution of Cu $^{2+}$ and Co $^{2+}$ for Fe $^{2+}$ in LuFe $_{2}$ O $_{4}$ destabilized the CO structure. In LuFeCuO $_{4}$ , there exist characteristic zigzag-shaped diffuse streaks and diffuse spots at the h/3- h/3- 0-type positions (h: integer, =0.06) in reciprocal space, which originate from static cationic ordering of Fe $^{3+}$ and Cu $^{2+}$ ions in the triangular lattice. Moreover, real-space images by the energy-filtered TEM revealed that nanometer-sized domain structures with the 510 nm size are formed. In contrast, honeycomb-shaped diffuse streaks were found in LuFeCoO $_{4}$ , in which no domain structures are observed in real-space images.

Journal Articles

Magnetic and dielectric properties of R $_{0.5}$ Ca $_{0.5}$ MnO $_{3}$ (R=Eu-Lu)

Yoshii, Kenji; Hiramitsu, Yusuke*; Yoneda, Yasuhiro; Okajima, Yuka; Nishihata, Yasuo; Mizuki, Junichiro; Ikeda, Naoshi*

Ferroelectrics, 379(1), p.183 - 190, 2009/05

https://doi.org/10.1080/00150190902852208

Times Cited Count：9 Percentile：39.82(Materials Science, Multidisciplinary)

The magnetic and dielectric properties of perovskite manganites R $_{0.5}$ Ca $_{0.5}$ MnO $_{3}$ (R=Eu-Lu) have been investigated. Their dielectric constants were about 1000 at around room temperature. Inflections or peaks of temperature dependences of the dielectric constants were observed at around the charge-ordering temperatures determined from the magnetic measurements. Analyses of tan and EXAFS spectra suggested that the dielectric properties of this system are due to a spatial arrangement and transfer of the Mn-3d electrons. The observation of a two-peak structure of tan indicates that dielectric measurement can be used to observe homogeneity or in homogeneity of sample, as mentioned in our previous paper.

Journal Articles

Stoichiometric study of the dielectric and magnetic properties in charge frustrated system LuFe $_{2}$ O $_{4}$

Michiuchi, Takamasa*; Yokota, Yusuke*; Komatsu, Takuma*; Hayakawa, Hironori*; Kuroda, Tomoko*; Maeda, Daisuke*; Matsuo, Yoji*; Mori, Shigeo*; Yoshii, Kenji; Hanasaki, Noriaki*; et al.

Ferroelectrics, 378(1), p.175 - 180, 2009/00

https://doi.org/10.1080/00150190902859187

Times Cited Count：18 Percentile：59.66(Materials Science, Multidisciplinary)

We have synthesized the samples of LuFe $_{2}$ O $_{4}$ , which shows the ferroelectricity due to charge ordering of Fe ions, under several different reducing conditions using a CO $_{2}$ -CO flow. The reducing condition was changed by changing a flow ratio of CO $_{2}$ and CO. It was found that the flow ratio of CO $_{2}$ /CO of about 5 provided the sample with the highest magnetic transition temperature of 240-250 K. This sample showed the dielectric constant of 10000 at room temperature. The imaginary part of the dielectric response offered the activation energy of 0.4-0.5 eV, which is slightly larger than that reported previously (about 0.3 eV). We will perform further investigation of the physical properties of this sample to clarify full details and their origin of LuFe $_{2}$ O $_{4}$ .

Journal Articles

X-ray topography of piezoelectric LaTa $_{0.5}$ Ga $_{5.5}$ O $_{14}$ crystal grown by Czochralski method

Yoneda, Yasuhiro; Mizuki, Junichiro; Takeda, Hiroaki*; Shiosaki, Tadashi*

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 55(5), p.971 - 974, 2008/05

We performed synchrotron X-ray topography on a LaTa $_{0.5}$ Ga $_{5.5}$ O $_{14}$ (LTG) crystal grown by the Czochralski (Cz) method. Since the synchrotron X-ray source can provide high-energy X-rays, one can detect bulk-sensitive information by the X-ray topography. LTG is one of the most attractive piezoelectric crystals like La $_{3}$ Ga $_{5}$ SiO $_{14}$ (LGS), because of excellent acoustic properties (temperature compensation of acoustic losses). Since LTG single crystals can be grown from stoichiometric melt, single crystals with good crystal quality can be obtained comparing to LGS which can not be grown from stoichiometric system but from congruent melt. The 60-keV X-ray topography revealed that the LTG crystal quality was not the same crystalline quality. The crystal quality of a center parts was worse than that of surroundings.

Journal Articles

Electronic ferroelectricity from charge ordering in RFe $_{2}$ O $_{4}$

Ikeda, Naoshi*; Matsuo, Yoji*; Mori, Shigeo*; Yoshii, Kenji

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 55(5), p.1043 - 1045, 2008/05

We report our recent discovery of novel ferroelectricity arising from the polar ordering of Fe $^{3+}$ and Fe $^{2+}$ in a mixed valence triangular lattice oxide LuFe $_{2}$ O $_{4}$ , where the electric polarization is not a result of ionic displacement. The polar ordering of Fe $^{3+}$ and Fe $^{2+}$ was confirmed with a resonant X-ray scattering study in SPring-8. The origin of such ordering is the competitive interaction between Fe $^{3+}$ and Fe $^{2+}$ in the triangular lattice, i.e., the charge frustration. The polar superlattice of Fe $^{3+}$ and Fe $^{2+}$ develops below 350 K, where the electric polarization appears. The ferroelectricity arising from the polar charge ordering or the polar electron distribution may have great potential for the future application of ferroelectrics.

Journal Articles

Ferroelectric domain structures in BiFeO $_{3}$ -BaTiO $_{3}$

Kitagawa, Shuji*; Ozaki, Tomoatsu*; Horibe, Yoichi*; Yoshii, Kenji; Mori, Shigeo*

Ferroelectrics, 376(1), p.122 - 128, 2008/00

https://doi.org/10.1080/00150190802440948

Times Cited Count：16 Percentile：56.61(Materials Science, Multidisciplinary)

Microstructures associated with the ferroelectric (FE) properties in (1-x)BiFeO $_{3}$ -xBaTiO $_{3}$ were investigated mainly by a transmission electron microscopy. It was found that large FE domains in BiFeO $_{3}$ changed into complicated FE microdomains with the 20-30 nm width in the x = 0.25 compound. The directions of the spontaneous polarization in each FE microdomains were determined by obtaining dark-field images. Changes of the FE microdomains for x = 0.28 composition as a function of the temperature were also investigated.

Journal Articles

Magnetic and ferroelectric properties of (Bi $_{1-x}$ La)FeO

Yoneda, Yasuhiro; Yoshii, Kenji; Saito, Hiroyuki; Mizuki, Junichiro

Ferroelectrics, 348, p.33 - 37, 2007/03

https://doi.org/10.1080/00150190701196096

Times Cited Count：11 Percentile：47.11(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Ferroelectricity from valence ordering in RFe $_{2}$ O $_{4}$

Ikeda, Naoshi*; Mori, Shigeo*; Yoshii, Kenji

Ferroelectrics, 348, p.38 - 47, 2007/03

https://doi.org/10.1080/00150190701196112

Times Cited Count：2 Percentile：12.52(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

PDF analysis of Bi $_{0.9-x}$ La $_{0.1}$ Tb $_{x}$ FeO $_{3}$

Yoneda, Yasuhiro; Yoshii, Kenji; Saito, Hiroyuki; Mizuki, Junichiro

Ferroelectrics, 355, p.119 - 124, 2007/01

https://doi.org/10.1080/00150190701517366

Times Cited Count：2 Percentile：12.52(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Magnetically induced ferroelectricity in multiferroic compounds of MnO

Kimura, Hiroyuki*; Kobayashi, Satoru*; Wakimoto, Shuichi; Noda, Yukio*; Kon, Keiichiro*

Ferroelectrics, 354, p.77 - 85, 2007/01

https://doi.org/10.1080/00150190701454602

Times Cited Count：24 Percentile：67.31(Materials Science, Multidisciplinary)

A review is given on the studies of magnetic properties and dielectric properties as functions of temperature and magnetic field for various multiferroic MnO ( = rare-earth) compounds. We have observed successive dielectric and magnetic phase transitions which concomitantly take place and a so-called multiferroics is realized. In this system, the ferroelectricity is magnetically induced and the commensurate magnetism is indispensable to produce a spontaneous electric polarization. The microscopic origin of the magnetically induced ferroelectricity and the role of the rare-earth magnetic moment for a colossal magnetoelectric effect in MnO will be discussed in the viewpoint of the magnetic structure.

Journal Articles