Abstract
Effects of post-sintering cooling rate from liquid quenching to slow air cooling were investigated for the low- T c 2212 phase in the Bi-Sr-Ca-Cu-O system. The fastest cooling rate yielded the 2212 granular phase with the highest superconductive T c . The change in T c is attributed mainly to the change in oxygen stoichiometry. The difference between the granular and bulk T c 's was smallest after slow cooling, even though the granular T c then had its lowest value. No variation in lattice parameters was observed by powder X-ray diffraction. When the samples were quenched, structural imperfections were introduced; these could not be eliminated even by long-term annealing and slow cooling in air. The lowering of T c was inhibited by the presence of these imperfections in the crystal structure of the 2212 phase. It is emphasized that the true granular superconductive properties are best observed by magnetic measurements since bulk resistivity measurements may lead to erroneous conclusions.
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