Synthesis of High Purity Bi(Pb)2223 Tapes With High $T_{\rm c}$ Above 115 K

Enhancement of J_c has been always expected for Bi(Pb)2223 tapes for their extensive applications. Among several strategies to improve critical current properties, enhancement of T_c by control of nonstoichiometric cation composition is one of the most promising ways. In the present study, we have attempted to enhance T_c of silver-sheathed Bi(Pb)2223 tapes by control of starting compositions and heat-treatment conditions. The T_c^onset of the Bi(Pb)2223 tapes starting from nearly stoichiometric cation composition was enhanced up to 115.2 K by post-annealing at 700 ^°C in moderately reducing atmospheres and generation of Pb3221 phase was suppressed during the annealing. Moreover, introduction of the pre-annealing process further improved T_c after post-annealing. T_c^onset up to 115.2 K with sharp superconducting transition was achieved in a multi-filamentary tape with nearly stoichiometric cation composition.