YBa_2Cu_3O_<7-y>ペロブスカイトの酸素欠損と超伝導

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Ten YB_a2Cu_3O_<7-y> (YBCO) perovskite samples with varying oxygen deficiency (0.15<y<1) were prepared by changing the quenching temperature or annealing conditions. With increasing quenching temperature, the transition temperature (T_c) for superconductivity decreased. This is accompanied by increasing oxygen deficiency and changes in the lattice constants. The oxygen deficiency of the sample annealed under nitrogen atmosphere at 700℃ was more than that of the sample quenched at 950℃. There were no differences observed between the oxygen deficiency, lattice constants, nor superconductivity of the sample annealed under oxygen atmosphere and that. cooled slowly from 350℃ (0.5℃/min) in air. Annealing under high oxygen pressure caused destruction of the YBCO structure and disappearance of the superconductivity. Considering all the experimental results obtained in this study, YBCO perovskite can be classified into three types : Ortho-I(y<0.2) . Ortho-II(0.2 <y<0.5), and Tetra (0.5 <y<1). Ortho-I type shows superconductivity with a T_c of around 90 K, while the T_c onset of Ortho-II is below 70 K. Although oxygen deficiency and lattice constants change continuously, a discontinuous T_c change is observed when YBCO changes from Ortho-I to Ortho-II. Tetragonal type is semiconductive and is not super conductive above 4 K. The small difference in the oxygen deficiency between Ortho- I and Ortho-II indicates that it is necessary to minimize the oxygen deficiency in order to obtain a uniform material with a T_c of 90 K. However, annealing under_ oxygen does not modify the superconductivity of samples cooled slowly.
社団法人日本セラミックス協会の論文
1988-04-01

YBa_2Cu_3O_<7-y>ペロブスカイトの酸素欠損と超伝導

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