研究者詳細 - 村岡　祐治

論文 - 村岡　祐治

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Structural phase transition in the superconducting pyrochlore oxide Cd2Re2O7 査読

M Hanawa, J Yamaura, Y Muraoka, F Sakai, Z Hiroi

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 63 ( 6-8 ) 1027 - 1030 2002年6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：PERGAMON-ELSEVIER SCIENCE LTD

We report a structural phase transition found at T-s = 200 K in a pyrochlore oxide Cd2Re2O7 which shows superconductivity at T-c = 1.0 K. X-ray diffraction experiments indicate that the phase transition is of the second-order, from a high-temperature phase with the ideal cubic pyrochlore structure (space group Fd (3) over barm) to a low-temperature phase with another cubic structure (space group F (4) over bar 3m). It is accompanied by a dramatic change in the resistivity and magnetic susceptibility and thus must induce a significant change in the electronic structure of Cd2Re2O7. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00090-2

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Metal-insulator transition of VO2 thin films grown on TiO2 (001) and (110) substrates 査読

Y Muraoka, Z Hiroi

APPLIED PHYSICS LETTERS 80 ( 4 ) 583 - 585 2002年1月

Superconductivity at 1 K in Cd2Re2O7 査読

M Hanawa, Y Muraoka, T Tayama, T Sakakibara, J Yamaura, Z Hiroi

PHYSICAL REVIEW LETTERS 87 ( 18 ) 187001 2001年10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：AMER PHYSICAL SOC

We report the first pyrochlore oxide superconductor Cd2Re2O7. Resistivity, magnetic susceptibility, and specific heat measurements on single crystals evidence a bulk superconductivity at 1 K. Another phase transition found at 200 K suggests, that a peculiar electronic structure lies behind the superconductivity.

DOI： 10.1103/PhysRevLett.87.187001

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Atomic ordering in the LaFe0.5Mn0.5O3 solid solution film 査読

K Ueda, Y Muraoka, H Tabata, T Kawai

APPLIED PHYSICS LETTERS 78 ( 4 ) 512 - 514 2001年1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：AMER INST PHYSICS

LaFe0.5Mn0.5O3 solid solution films have been formed on SrTiO3 (111) substrates using a pulsed laser deposition technique and their magnetic properties have been examined. The films showed ferromagnetic (or ferromagnetic) behavior with a Curie temperature of 380 K and the saturation magnetization was estimated to be about 1.5 mu (B) per magnetic ion site (B site). The x-ray photoemission spectra indicated that this behavior was due to the partial ordering of magnetic ions (Fe and Mn ions) which is caused by the charge disproportion between Fe and Mn ions under the film formation conditions. (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1343844

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Effects of light-irradiation on spin-glass state and magnetoresistive properties of Zn0.5Co0.5Fe2O4 spinel ferrite films 査読

Y Muraoka, H Tabata, T Kawai

SOLID STATE COMMUNICATIONS 120 ( 5-6 ) 255 - 258 2001年

Room-temperature spin glass and its photocontrol in spinel ferrite films 査読

Y Muraoka, H Tabata, T Kawai

APPLIED PHYSICS LETTERS 77 ( 24 ) 4016 - 4018 2000年12月

Photoexcited spin-glass state in (Mg, Fe){Mg,Fe,Ti}O-4 spinel ferrite films 査読

Y Muraoka, H Tabata, T Kawai

JOURNAL OF APPLIED PHYSICS 88 ( 12 ) 7223 - 7229 2000年12月

Preparation and thickness dependence of magnetic properties of (111)-oriented Mg1.5FeTi0.5O4 spinel films on sapphire by pulsed laser deposition technique 査読

Y Muraoka, K Ueda, H Tabata, T Kawai

VACUUM 59 ( 2-3 ) 622 - 627 2000年11月

HRTEM and Micro-Raman Studies on Superconducting−Superionic Conducting Nanohybrid, Ag1.17I1.54Bi2Sr2CaCu2Oy 査読

Jin-Ho Choy, Young-Il Kim, Seong-Ju Hwang, Yuji Muraoka, Naoyuki Ohnishi, Kenji Hiraga, Pham V. Huong

The Journal of Physical Chemistry B 104 ( 39 ) 9086 - 9090 2000年10月

Consolidation of Bi-Sr-Ca-Cu-O superconductors by the shock-loading method 査読

M Kikuchi, H Faqir, S Kawamata, K Okuda, Y Muraoka, K Fukuoka, Y Syono

SUPERCONDUCTOR SCIENCE & TECHNOLOGY 13 ( 8 ) 1151 - 1154 2000年8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：IOP PUBLISHING LTD

Shock compaction experiments were carried out for Bi2223 to prepare a dense, oriented bulk specimen. The shocked specimen exhibited a high degree of crystallographic orientation and a high density, above 96%. The optimal condition of the crystallographic orientation was attained at a shock pressure of 5 GPa and at annealing temperatures between 750 and 800 degrees C. The post annealing of a specimen shocked at 5 GPa was effective in increasing Delta M, indicating the introduction of pinning sites. The magnetic torque measurements showed that a high degree of orientation was attained and many pinning centres were induced by the shock loading.

DOI： 10.1088/0953-2048/13/8/307

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Photocontrol of spin-glass state in Mg1.5FeTi0.5O4 spinel ferrite films 査読

Y Muraoka, H Tabata, T Kawai

APPLIED PHYSICS LETTERS 76 ( 9 ) 1179 - 1181 2000年2月

Preparation of -MnO2 with an open tunnel 査読

Y Muraoka, H Chiba, T Atou, M Kikuchi, K Hiraga, Y Syono, S Sugiyama, S Yamamoto, JC Grenier

J. Solid State Chem. 144 ( 1 ) 136 - 142 1999年4月

Preparation of hexagonal MoO3 by "Chimie Douce" reaction with NO2 査読

Y Muraoka, JC Grenier, S Petit, M Pouchard

SOLID STATE SCIENCES 1 ( 2-3 ) 133 - 148 1999年3月

New synthetic routes for preparing perovskites - Electrochemical oxidation and oxidation by NO2 査読

JC Grenier, JP Doumerc, Y Muraoka, S Petit, M Pouchard, A Wattiaux

SOLID STATE IONICS 108 ( 1-4 ) 9 - 15 1998年5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：ELSEVIER SCIENCE BV

Two new synthetic low temperature routes for preparing perovskite-related materials, especially metastable phases are depicted. The first one, the electrochemical oxidation, uses the electric field as the driving force for intercalating oxygen atoms within parent oxide networks. The reaction is achieved under anodic potential, in alkaline solution (1 M KOH or NaOH), at room temperature, in air. This process has been used for preparing various perovskite compounds such as AMO(3) (A = Sr, La; M = Fe1-x Co-x) or A(2)MO(4+delta) (A = La, Nd, Sr). The most relevant results are reported. Potentiostatic and galvanostatic experiments have shown that the amount of intercalated oxygen can be controlled and that the process is reversible. Structural as well as electronic aspects of the oxygen intercalation are discussed and a reaction mechanism is proposed. The second route is based on the exothermic reaction of nitrogen dioxide NO2 with NH4+ ions at moderate temperatures (typically T < 300 degrees C), which allowed the destruction of NH4+ cations in situ. Topotactic reactions are described for preparing new hexagonal forms of WO3 or MoO3. The reaction process is discussed. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0167-2738(98)00012-5

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New "chimie douce" oxidizing processes: Electrochemical oxidation and in situ oxidation by NO2 査読

Jean-Claude Grenier, Jean-Pierre Doumerc, Yuji Muraoka, Stephane Petit, Michel Pouchard, Alain Wattiaux, Fang Zhou

Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals 311 359 - 366 1998年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Taylor and Francis Inc.

Two new oxidation processes are described : the electrochemical oxidation in alkaline solution uses the electrical potential as the driving force for intercalating oxygen, at room temperature, into oxide networks such as perovskites or Ln2MO4 (M = Ni, Cu) compounds. The second one is based on the in situ destruction of ammonium ions in oxide lattices by interaction with NO2 gas, at moderate temperatures. Pictures of the reaction mechanisms are also proposed. © 1993 OPA (Overseas Publishers Association) Amsterdam B.V. Published under license under the Gordon and Breach Science Publishers imprint.

DOI： 10.1080/10587259808042411

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Growth of high-quality Bi2Sr2CaCu2Oz crystal and characterization 査読

H Faqir, G Vacquier, H Chiba, M Kikuchi, Y Muraoka, Y Syono

JOURNAL OF MATERIALS RESEARCH 12 ( 10 ) 2522 - 2525 1997年10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：MATERIALS RESEARCH SOCIETY

We report growth of high-quality Bi2Sr2CaCu2Oz single crystals with dimensions 2 x 1 x 0.03 mm(3) with a melt and growth technique. The composition of this crystal is homogeneous and very close to the stoichiometric composition. Structure characterization of a single crystal was realized by measuring the (001) x-ray diffraction. The lattice parameters of a typical crystal are a = 5.414(2) Angstrom, b = 5.413(2) Angstrom, and c = 30.823(10) Angstrom. The superconducting temperature T-c = 95 K with a sharp transition width (10-90% level) between 6 and 10 K was determined from resistivity and de susceptibility. We have measured the magnetization of Bi2Sr2CaCu2Oz single crystal under magnetic field applied along the c-axis. The anomalous second peak effect appeared between 20 and 30 K. We discuss the qualities of these crystals.

DOI： 10.1557/JMR.1997.0334

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Ferromagnetism and large negative magnetoresistance in Bi1-xCaxMnO3 (x>=0.8) perovskite 査読

H Chiba, M Kikuchi, K Kusaba, Y Muraoka, Y Syono

SOLID STATE COMMUNICATIONS 99 ( 7 ) 499 - 502 1996年8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：PERGAMON-ELSEVIER SCIENCE LTD

Polycrystalline perovskite manganites Bi1-xCaxMnO3 (x greater than or equal to 0.8) have been prepared by standard ceramic technique, and their magnetic and electronic property are examined down to 5 K. Ferromagnetic moment and reduced resistivity are observed for Bi1-xCaxMnO3 (x greater than or equal to 0.875), and also large negative magnetoresistances appear below T-c. Copyright (C) 1996 Elsevier Science Ltd

DOI： 10.1016/0038-1098(96)00305-5

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AgI-intercalation into Bi2Sr2CaCu2Oz compound 査読

Y Muraoka, N Ohnishi, M Nagoshi, Y Morioka, M Kikuchi, K Hiraga, N Kobayashi, Y Syono

PHYSICA C 263 ( 1-4 ) 193 - 196 1996年5月

Synthesis conditions and superconductivity of Pb0.7Cu0.3Sr2Y0.5Ca0.5Cu2Oy 査読

M Kikuchi, M Shida, E Ohshima, Y Muraoka, Y Syono

PHYSICA C 263 ( 1-4 ) 204 - 207 1996年5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：ELSEVIER SCIENCE BV

Pb0.7Cu0.3Sr2Y0.5Ca0.5Cu2Oy was synthesized as a mother specimen in air and then annealed under two different experimental conditions, in an oxidizing and in a reducing condition. The mother specimen was a nonsuperconductor, but both annealed specimens, one quenched from high temperature and the other treated in high-pressure O-2, were superconductors with T-c's of about 50 K and about 60 K, respectively. The low Cu-valence of the quenched specimen which showed superconductivity suggests a decrease in the Pb-valence, while the high T, of the specimen treated in high-pressure O-2 would be explained by high Cu-valence and Pb4+.

DOI： 10.1016/0921-4534(95)00824-1

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STRUCTURE AND SUPERCONDUCTIVITY OF IODINE-INTERCALATED BI2SR4CU2CO3OZ 査読

Y MURAOKA, H NAMEKI, M KIKUCHI, S AWAJI, N KOBAYASHI, Y SYONO

PHYSICA C 233 ( 1-2 ) 209 - 213 1994年11月

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