Improvement of superconducting characteristics of a Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 2//Ag thick film by controlling the microstructure under reduced O/sub 2/ atmosphere

The partial melting and slow cooling heat-treatment for a Bi-2212 thick film was carried out in 7% and 1% oxygen partial pressure. In 1% O/sub 2/ atmosphere, the partial melting point lowered below 850/spl deg/C. When cooling under 1% O/sub 2/, large Bi-free phases which were observed in samples heat-treated in air disappeared, resulting in the formation of this phase on the surface. Reduction of Ca and Cu concentration from stoichiometric composition is also effective to suppress the formation of Bi-free phases. The highest J/sub c/ value of 1.13/spl times/10/sup 5/ A/cm/sup 2/ at 4.2K in 4 T was obtained in a sample with the composition of Bi/sub 2.0/Sr/sub 2.2/Ca/sub 0.8/Cu/sub 1.9/O/sub x/ prepared in 1% O/sub 2/.<>