Preparation of Bi, Pb-Sr-Ca-Cu-O superconductor by the sol-gel method

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The high -Tc superconducting phase in the Bi, Pb-Sr-Ca-Cu-O system has been prepared by the sol-gel method. The formation process of the low-Tc phase as well as the high-Tc phase has been examined by thermal analysis, infra-red measurements and X-ray diffraction, and compared with the conventional solid-state reaction. At a low heat-treatment temperature of 400 ° C, Bi2O3, CaCO3 and CuO are precipitated from the gel. These oxides react with each other to form several double oxides above 600 ° C and yield the low-Tc phase as a main product at 800 ° C. The heat treatment at higher temperatures effectively leads to the formation of the high-Tc phase. In particular, the high-Tc phase is most predominantly formed in the specimen heat treated at 845 ° C for 48 h after calcination at 800 ° C for 12 h, which is reflected in the critical temperature of 104 K. The temperature at which the low-Tc phase is formed is lower in the sol-gel-derived sample than in the specimen prepared by the solid-state reaction. Further-more, the sol-gel method brought about a larger amount of the high-Tc phase than the solid-state reaction when the conditions for the heat treatment were identical. These facts clearly indicate the superiority of the sol-gel method for the formation of both high-Tc and low-Tc Bi, Pb-Sr-Ca-Cu-O superconducting phases.