Bi (Pb)系酸化物超伝導体の焼結挙動と臨界電流密度に及ぼすアルカリ土類酸化物の添加効果

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The sintering behavior and superconducting properties of the high Tc phase in the Bi(Pb)-Sr-Ca-Cu-O system were investigated using the starting powder with a composition Bi1.8Pb0.4Sr2.0-Ca2.0Cu3.2Oy, which was added to by 0.10mol or 0.15mol of MgO, CaO, SrO and BaO each, then pressformed at 2000kg/cm2 or 5000kg/cm2 and sintered at 850°C or 860°C for 120hr. The influence of the CaO additive was examined in detail in the range of x=0.0-0.7 for Bi1.8Pb0.4Sr2.0Ca2.0+xCu3.2Oy. Bulk densities of 4.8-4.9g/cm2 were obtained in the oxide added systems that were press-formed at 5000kg/cm2 and sintered at 850°C, while Tc was nearly constant at 107-111K. Jc measured at 77K ex-ceeded 500A/cm for both the MgO and CaO added systems. With increasing additive content (x) the bulk density of the above CaO additive system decreased from 4.8 to 4.lg/cm2 at 850°C and from 4.7 to 4.3g/cm2 at 860°C. Tc(zero resistance) increased with increasing x, suggesting that the amount of the coexisting low Tc phase was decreased. The Jc(77K) value increased with x and attained a maximum of 1100A/cm2 at x=0.4 sintered at 850°C and at x=0.6 sintered at 860°C, 4-5 times higher than that of x=0.0.
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