研究者詳細 - 池田　直

論文 - 池田　直

分割表示 209 件中 181 - 200 件目／全件表示 >>

X-ray absorption spectroscopy in NaCo2O4, LaCoO3 and SrCoO3 査読

T Matsushita, M Mizumaki, N Ikeda, M Nakazawa, A Agui, Y Saitoh, T Nakatani, A Yoshigoe, S Nakamura

SURFACE REVIEW AND LETTERS 9 ( 2 ) 1327 - 1331 2002年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WORLD SCIENTIFIC PUBL CO PTE LTD

We have performed Co 2p X-ray absorption spectroscopy (XAS) on a mixed valence hexagonal layered system NaCo2O4, which shows large thermopower and metallic conductivity. We also measured XAS for SrCoO3 and LaCoO3 as examples of typical Co ionic states. The Co ions of the last two materials are octahedrally surrounded by oxygen atoms. A Co atom in NaCo2O4 also has octahedral coordination with oxygen atoms but it is distorted slightly. The Co ions in SrCoO3 and LaCoO3 are in the d(5) and d(6) configuration respectively. The spectrum of NaCo2O4 resembles that of LaCoO3 rather than that of SrCoO3; the Co ions in NaCo2O4 can be regarded as the d(6) configuration. Also, we have tried to calculate the XAS spectra by using the charge-transfer multiplet model (CT-M). Although we could not find out the best-fitting parameters, the results suggested the itinerancy of the Co 3d states.

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Dielectric and structure properties of charge competing system YFe 2O4

Naoshi Ikeda, Ryosuke Mori, Kay Kohn, Masaichiro Mizumaki, Takahiro Akao

Ferroelectrics 272 309 - 314 2002年1月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Taylor and Francis Inc.

YFe2O4-δ ( δ &lt
0.005), which is a member of charge-frustrated system RFe 2 O 4 was synthesized and investigated by the low-temperature synchrotron powder X-ray diffraction. The structure between 225K and 250K is the same with the three-dimensional charge ordered state of LuFe 2 O 4 . Below the charge ordering temperature, at least five different phase transitions were detected. Since the balance of competing interaction between ionic charge essentially dominates the presence of multi phases in frustrated system, the low oxygen deficiency in YFe2O 4-δ is considered as the origin of the multi phases in low temperature. © 2002 Taylor &amp
Francis.

DOI： 10.1080/713716255

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Accurate Measurement of Lattice Parameters on YMn₂O₅ 査読

Isao Kagomiya, Naoshi Ikeda, Yukio Noda, S. Matsumoto, Yoshikazu Fukuda, Hiroyuki Kimura, Kay Kohn

SPring-8 User Experiment Report 7 26 - 26 2001年4月

X-ray Diffraction Study on Ca_{2 x}Y_2-xCu₅O₁₀ 査読

H. Yamaguchi, Hiroyuki Kimura, Masashi Watanabe, Yoshikazu Fukuda, Naoshi Ikeda, Yukio Noda

SPring-8 User Experiment Report 6 18 - 18 2001年4月

Single Crystal Analysis of High-Pressure Phase of Solid Oxygen 査読

Y. Akahama, E. Uemura, M. Harada, H. Kawamura, Masashi Watanabe, Yukio Noda, Naoshi Ikeda, Osamu Shimomura

SPring-8 User Experiment Report 7 22 - 22 2001年4月

Development of BL02B1 査読

Naoshi Ikeda, Y. Yoneda, Takahisa Shobu, Hiroyuki Kimura, Masashi Watanabe, Yoshikazu Fukuda, Isao Kagomiya, S. Matsumoto, Yukio Noda

SPring-8 User Experiment Report 6 23 - 23 2001年4月

"Devil's staircase"-type phase transition in NaV2O5 under high pressure 査読

Ohwada K, Fujii Y, Takesue N, Isobe M, Ueda Y, Nakao H, Wakabayashi Y, Murakami Y, Ito K, Amemiya Y, Fujihisa H, Aoki K, Shobu T, Noda Y, Ikeda N

PHYSICAL REVIEW LETTERS 87 ( 8 ) 2001年

Charge Frustration and Dielectric Dispersion in LuFe2O4

Ikeda Naoshi, Kohn Kay, Myouga Nobuyuki, Takahashi Eri, Kitôh Hijiri, Takekawa Shunji

Journal of the Physical Society of Japan 69 ( 5 ) 1526 - 1532 2000年5月

記述言語：英語出版者・発行元：一般社団法人日本物理学会

We report the dielectric anomaries at the phase transitions ofLu(Fe2+ Fe3+)O4, which is considered as a charge andspin frustrated system.Dielectric constant shows a hump, just above the transition from thehigh temperature two-dimensional to the low temperaturethree-dimensional charge ordering. A few glassy behaviors wereobserved at this transition. The presence of spontaneous polarizationin the low temperature phase was confirmed by the measurement ofpyroelectricity. A step-wise increase of the dielectric constant withincreasing temperature was observed between 150 K and 250 K as inother RFe2O4.These phenomena are explained by the presence of the polar domainswith the ordering of Fe2+ and Fe3+ and the motions of theantiphase boundaries between them.

DOI： 10.1143/JPSJ.69.1526

CiNii Article

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X-ray diffuse scattering study on charge-localized states

S. Shimomura, T. Tonegawa, K. Tajima, N. Wakabayashi, N. Ikeda, T. Shobu, Y. Noda, Y. Tomioka, Y. Tokura

Physical Review B - Condensed Matter and Materials Physics 62 ( 6 ) 3875 - 3878 2000年

掲載種別：研究論文（学術雑誌）

X-ray scattering measurements on (Formula presented) have revealed the existence of diffuse scattering above the charge and orbital ordering transition temperature (Formula presented) The diffuse scattering has local intensity maxima at incommensurate positions (Formula presented) With decreasing temperature, (Formula presented) increases from about 0.4, and it discontinuously changes to 0.5 at (Formula presented) Characteristic patterns of diffuse intensity distributions can be qualitatively interpreted by calculations based on distortion fields associated with the Jahn-Teller effect. The observed patterns are similar to those observed above the ferromagnetic insulator-metal transition temperature in (Formula presented) reported previously. © 2000 The American Physical Society.

DOI： 10.1103/PhysRevB.62.3875

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Synchrotron observation of the charge ordering and spontaneous polarization in LuFe<inf>2</inf>O<inf>4</inf>

Naoshi Ikeda, Masahiko Tanaka, Hijiri Kitô, Satoshi Sasaki, Yasusada Yamada

Ferroelectrics 222 ( 1-4 ) 227 - 235 1999年

掲載種別：研究論文（学術雑誌）

We report a synchrotron orbital radiation study of a charge ordering in a triangular mixed valence system LuFe2O4. Using the X-ray anomalous dispersion method near the iron K-shell absorption edge, we confirmed a superstructure of Fe2+ and Fe3+ on the triangular lattice with a configuration of a √3 × √3 × 2 structure. This charge structure shows a spontaneous polarization. The existence of two dimensional charge ordering above 330K was deduced from the temperature dependence of the energy dispersion for the superlattice reflection.

DOI： 10.1080/00150199908014820

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Charge ordering in La1-xSrxMnO3 (x similar to 0.12) 査読

Inami T, Ikeda N, Murakami Y, Koyama I, Wakabayashi Y, Yamada Y

Japanese Journal of Applied Physics Part 1-Regular Papers Brief Communications & Review Papers 38 212 - 214 1999年

Charge ordering of LuFe<inf>2</inf>O<inf>4</inf> observed by an anomalous X-ray dispersion

Naoshi Ikeda, Shinichiro Nohdo, Yasusada Yamada, Eri Takahashi, Kay Kohn

Journal of the Korean Physical Society 32 ( SUPPL. 1 ) 1998年2月

掲載種別：研究論文（学術雑誌）

We observed a superlattice reflection for triangular layered oxide LuFe2O4 by using anomalous X-ray dispersion with synchrotron radiation source. We found that superlattice spot (1/3, 1/3, 4.5) shows a large intensity variation upon a slight change of incident X-ray energy (wave length) from 7.114 keV (1.7437 Å) to 7.1448 keV (1.7353 Å) across the Fe absorption edge. This phenomenon is explained by superlattice structure of Fe2+ and Fe3+ on triangular lattice. The existence of the superlattice structure due to the charge ordering of iron ions on triangular lattice indicates that LuFe2O4 possesses local spontaneous polarization.

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Valence fluctuation and polarization fluctuation in LuFe<inf>2</inf>O<inf>4</inf>

Yasusada Yamada, Naoshi Ikeda

Journal of the Korean Physical Society 32 ( SUPPL. 1 ) 1998年2月

掲載種別：研究論文（学術雑誌）

The anomalous dielectric behavior of mixed valence system LuFe2O4 is investigated. It has been shown that LuFe2O4 undergoes successive phase transitions associated with ordering of charge configuration of Fe ion following the sequence of disorder → 2D-CDW (charge density wave) → 3D-CDW state. The stable 3D-CDW phase is characterized by a long period incommensurate antiferroelectric phase. The anomalously high dielectric constant at lower temperature as well as its frequency dependence is discussed in connection with the motion of the antiphase domain boundaries.

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Dielectric dispersion and charge ordering of LuFe<inf>2</inf>O<inf>4</inf>

Eri Takahashi, Kay Kohn, Naoshi Ikeda

Journal of the Korean Physical Society 32 ( SUPPL. 1 ) 1998年2月

掲載種別：研究論文（学術雑誌）

A layer-structure oxide LuFe2O4 shows dielectric dispersions in two temperature regions below and above the transition between two- and three-dimensional charge orderings proposed by a diffraction study. The origin of the dispersions are considered to be related with electron hopping between Fe2+ and Fe3+ ions ordered or disordered on triangular lattices characteristic of this oxide.

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Incommensurate Charge Ordering in Charge-Frustrated LuFe<inf>2</inf>O<inf>4</inf> System

Yasusada Yamada, Shinichiro Nohdo, Naoshi Ikeda

Journal of the Physical Society of Japan 66 ( 12 ) 3733 - 3736 1997年

掲載種別：研究論文（学術雑誌）

The charge ordering process of a mixed valence LuFe2O4 system has been studied, focusing attention on the frustration effect associated with the charge configuration, ft is revealed that the system undergoes successive phase transitions following the sequence of disorder→2D CDW→3D CDW. In the 2D-CDW state, the charge density wave defined by the wave vector (1/3,1/3), is formed in the hexagonal layer. On the nodal lines of the CDW, the charge order is still undetermined due to the charge frustration. From a dielectric viewpoint, this phase is viewed as random stacking of 2D ferroelectric layers. In the 3D-CDW state, antiphase stacking of the 2D ordered layer develops. At the same time, the in-plane charge order exhibits a doubly modulated long-period structure. From a dielectric viewpoint, this phase is characterized by an incommensurate antiferroelectric phase. Relevance of the charge ordering mechanism to the observed anomalously large dielectric constant in LuFe2O4 is discussed. © 1997, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.66.3733

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Dipole glass behavior of RFe<inf>2</inf>O<inf>4</inf>

N. Ikeda, K. Odaka, E. Takahashi, K. Kohn, K. Siratori

Ferroelectrics 190 ( 1-4 ) 191 - 196 1997年

掲載種別：研究論文（学術雑誌）

We report low frequency dielectric dispersions of ErFe2O4 in which equal numbers of Fe2+ and Fe3+ ions occupy the sites on a triangular lattice. The first dispersion observed between 200 K and 300 K is explained qualitatively on a model that spontaneous polarization is present in the crystal below the Verwey transition. The second dispersion at higher temperatures is characterized by a few glass-like features. It was interpreted by successive freezing of the local dipole moments accompanied by short-range ordering of Fe2+ and Fe3+ ions.

DOI： 10.1080/00150199708014115

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Incommensurate charge ordering in mixed valence system LuFe<inf>2</inf>O<inf>4</inf>

Naoshi Ikeda, Yasusada Yamada, Shinichiro Nohdo, Toshiya Inami, Susumu Katano

Physica B: Condensed Matter 241-243 820 - 822 1997年

掲載種別：研究論文（学術雑誌）

Charge ordering of a mixed valence system LuFe2O4 has been studied by neutron scattering technique, focusing attention on the charge frustration effect on triangular lattice. It is revealed that the system undergoes successive phase transitions following the sequence of disorder → two-dimensional charge density wave state (2D-CDW) → three-dimensional charge density wave state (3D-CDW). In 2D-CDW state, the charge density wave defined by the wave vector (1/3 1/3) is formed in the hexagonal layer, © 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(97)00728-X

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Charge ordering in low-doping rate A<inf>1-x</inf>B<inf>x</inf>MnO<inf>3</inf> (A: La, Pr; B: Sr, Ca)

T. Inami, O. Hino, S. Nohdo, R. Kanao, N. Ikeda, Y. Yamada, S. Katano

Physica B: Condensed Matter 241-243 433 - 435 1997年

掲載種別：研究論文（学術雑誌）

We have found charge ordering in perovskite-type manganese oxides at low-carrier-doping region in neutron diffraction experiments. In La1-xSrxMnO3 (x = 0.1 and 0.15), we observed superlattice reflections at commensurate positions and the onset temperature Tp of the superlattice structure coincides with the low-temperature metal-toinsulator transition point. Pr1-xCaxMnO3 compounds are also studied at the stoichiometric concentration of x = 0.25. We observed diffuse satellite peaks indicating the existence of new charge-ordered state at this concentration. © 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(97)00611-X

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Anisotropy of Dielectric Dispersion in ErFe<inf>2</inf>O<inf>4</inf> Single Crystal

Naoshi Ikeda, Kay Kohn, Hijiri Kito, Jun Akimitsu, Kiiti Siratori

Journal of the Physical Society of Japan 64 ( 4 ) 1371 - 1377 1995年4月

掲載種別：研究論文（学術雑誌）

Dielectric dispersion was observed in a single crystal with the composition of ErFe2O3.95 below magnetic transition temperature. It is characterized by a large dielectric constant of the order of 104, and a Debye-type frequency dependence like in the poly crystalline samples of the same substance which we reported in a previous paper. Large anisotropy exists in the strength εs − ε∞ and the characteristic relaxation frequency of the dispersion. The strength is higher within the c-plane than along the c-axis, while the characteristic frequency is much larger along the c-axis than within the c-plane. The dielectric dispersion in the polycrystalline sample cannot be explained by a simple average of the single crystal results. The observed dispersion is qualitatively discussed with a model of domain wall motion on an assumption that ErFe2O4 is a polar crystal. © 1995, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.64.1371

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Magnetic Relaxation in Diluted Triangular Antiferromagnet LuFeMgO<inf>4</inf>

Naoshi Ikeda, Kay Kohn, Etsuko Himoto, Midori Tanaka

Journal of the Physical Society of Japan 64 ( 11 ) 4371 - 4377 1995年

掲載種別：研究論文（学術雑誌）

We observed a few magnetic relaxation phenomena in a LuFeMgO4single crystal, that is, the difference in the magnetization between field-cooled and zero-field-cooled specimens, the appearance of thermoremanent magnetization, and the frequency dependence of the cusp temperature of AC susceptibility. The observed relaxation was interpreted in terms of thermal fluctuations and freezing of the magnetic clusters which are supposed to exist in this substance. © 1995, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.64.4371

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