ホットプレス焼結によるBi-Pb-Sr-Ca-Cu-Oバルク超伝導体の緻密化と臨界電流密度

概要

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Bi_<1.84>Pb_<0.34>Sr_<2.03>Ca_<1.9>Cu_<3.06>O_y bulk superconductors were prepared by hot press sintering at 780°-820℃ at 4.9 MPa-24.5 MPa in air for 2 h. The relationship between the porosity (p) of the sample and hot pressing conditions was empirically formulated using the following equations, In (p)=-3Pt/(4η)+In (p_0), η=η_0 exp (E/RT), where P is the hot pressing pressure, t is the hot pressing time, ηis the viscosity, p_0 is the porosity of the compact body, E is the activation energy for viscous flow and T is the temperature. The values of η_0 and E were evaluated to be 80 Pa・s and 184 kJ/mol, respectively. With increasing bulk density, the resistivity at room temperature decreased and the critical temperature of each grain, which was evaluated from the temperature dependence of magnetization, decreased. The temperature dependence of resistivity greatly differed among samples with various bulk densities. The critical current density increased with increasing bulk density. The relationship between these superconducting properties and the bulk density was explained in terms of the two factors, that is, the increase in grain coupling strength and the decrease in oxygen content, which were caused by the densification of the sample.
社団法人日本セラミックス協会の論文
1992-03-01