Synthesis of a high T/sub c/ superconducting phase in Bi-Sr-Ca-Cu-O system

The synthesis of a high-T/sub c/ phase in the Bi-Sr-Ca-Cu-O system by the solid-state reaction and the J/sub c/ characteristics are reported. The partial pressure of oxygen near 0.1 atm is preferable as a sintering atmosphere, and Pb addition is effective to produce a large amount of high-T/sub c/ phase. Two classes of amorphouslike metastable superconducting phases with T/sub c/ of approximately 90 K and approximately 40 K, respectively, are found. It is thought that they have a randomly stacked structure. J/sub c/ of 93 A/cm/sup 2/ at zero field, 77 K is obtained for the sample with T/sub c/( rho =0)=107 K, which includes a high-T/sub c/ phase and a small amount of a low-T/sub c/ phase covered with the former phase. J/sub c/ is exponentially decreased by increasing the field. It is found that the transport J/sub c/ is limited by the weak-link regions in this system, as evidenced by the observation of a low resistive state above the J/sub c/ and of superconductivity in that state.<
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