| Project/Area Number |
07640460
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | IWATE UNIVERSITY |
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Principal Investigator |
IKEBE Manabu IWATE UNIV.Facul.Eng.Professor, 工学部, 教授 (40005955)
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| Co-Investigator(Kenkyū-buntansha) |
FUJISHIRO Hiroyuki IWATE UNIV.Facul.Eng.Associate Prof., 工学部, 助教授 (90199315)
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| Project Period (FY) |
1995 – 1996
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| Project Status |
Completed (Fiscal Year 1996)
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| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1996: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1995: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Keywords | High T_C Cuprates / Thermal Conductivity / Thermal Diffusivity / Electrical Resistivity / Phonon Scattering / Electron-Phonon Interaction / Stabilization of Superconductivity / 超伝導性の安定化 / 酸化物高温超伝導体 / 比熱 |
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| Research Abstract |
The thermal conductivity kappa (T), thermal diffusivity alpha (T) and electrical resistivity rho (T) of sintered Nd_<2-X>Ce_XCuO_4 (0<X<0.2) materials were measured. kappa (T) showed maximum nearthe Ce concentration X=0.15 at which the superconductivity occurred. A quenching process followed by annealing in Ar atmosphere was confirmed to stabilize superconductivity in Nd_<1.85>Ce_<0.15>CuO_4 crystals. Introduction of oxygen vacancies by "quench" process seems to play a key role for the stabilization of superconductivity. Annealing process in Ar atmosphere on "quench" ed samples reduces phonon scattering by point defects. The enhancement of T_c in these "quench+anneal" samples is consistent with the reduction of the competing effect of electron localization. From the analyzes of the thermal conductivity kappa (T), the point defect density is smaller in superconductive "quench+anneal" sample than non-superconductive as-sintered ("as-sinter") sample, while rho (T) values of "quench+anneal" samples are larger than those of "as-sinter" one. Some additional scattering mechanism such as due to antiparamagnons may be operative in superconducting samples. The thermal conductivity of La_<2-X>M_XCuO_4 (M=Ba, Sr) sintered materials was measured for the various concentrations of Ba and the phonon thermal conductivity was analyzed comparing with that of Nd_<2-X>Ce_XCuO_4. The pretty large kappa value for pure La_2CuO_4 was drastically diminished by substituting La by a small amount of Ba atoms especially at low temperatures. It was found that a new type of the phonon scattering center such as a two-level tunneling must be taken account of in order to explain the observed kappa reduction.
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