| Project/Area Number |
12450274
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Composite materials/Physical properties
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
YOSHIDA Katsukuni Kyoto University, Graduate School of Energy Science, Professor, エネルギー科学研究科, 教授 (70027142)
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| Co-Investigator(Kenkyū-buntansha) |
UEDA Sizumasa Kyoto University, Institute of Advanced Energy, Research Associate, エネルギー科学研究科, 助手 (00093196)
HACHIYA Kan Kyoto University, Graduate School of Energy Science, Research Associate, エネルギー科学研究科, 助手 (90314252)
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| Project Period (FY) |
2000 – 2002
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| Project Status |
Completed (Fiscal Year 2002)
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| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,900,000)
Fiscal Year 2002: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2001: ¥2,900,000 (Direct Cost: ¥2,900,000)
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| Keywords | non-ohmic resistance / nanostructural inhomogeneity / complex cuprates / percolation / superconducting network / negative resistance / nano-composites / 非オーム抵抗 / 高温超伝導体 / 複合銅酸化物 / ナノクラスター / 銅酸化物 / 高温超伝導 / 化合物複合体 / プラセオジム |
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| Research Abstract |
Non-ohmic conduction has been found for nano-composites Gd_<1-x>Pr_xBa_2Cu_3O_y (GPBCO), Nd_<1-x>Pr_xBa_2Cu_3O_y (NPBCO) and Ho_<1-x>Pr_xBa_2Cu_3O_y, (HPBCO) with Pr-concentration x=0〜0.8, and this phenomenon has been investigated in reference to structural inhomogeneity. At x above the percolation threshold x_<pc>, the electrical resistance ρ has been found to considerably depend on the current I. Its dependence is classified into three types. Around x_<pc>, ρ increases with I, showing a power law. At higher x,ρ becomes ohmic. At sufficiently high x,ρ becomes non-ohmic again, but changes into a decreasing function of I (negative resistance). This non-ohmic resistance is regarded as a phenomenon typical to the nanostructural inhomogeneity in the composite RPBCO. In particular the negative resistance results from the local Joule heat due to the structural inhomogeneity, which causes elevation of the local temperature from the ambient one, giving a lower resistance. These resistances hav
… More
e been revealed to originate in a current distribution characterized by the inhomogeneity, The mixture of Yba_2Cu_3O_y- and PrBa_2Cu_3O_y -grains in size of micron (YBCO and PBCO) has a resistance considerably governed by the presence of the third phase Y_<1-x>Pr_xBa_2Cu_3O_y(YPBCO) yielded around the initial grain boundaries. The resistance is strongly featured by a drop in ρ at the onset temperature T_<c1> and a shoulder of the ρ -T curve. This drop describes the granular superconductivity of YBCO grains, and the shoulder depicts emerging of YPBCO. These features correlate with each other, and thereby the textural structure of the composite can easily be controlled by changing sintering temperature and sintering time on sample preparation, creating a large variety of electrical characteristics. Dopant Pr with low concentration in YBCO has been found to enhance the critical current in the presence of magnetic field. This effect is explained in terms of a field induced pinning centers formed at Pr sites. Less
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