Enhanced Tc of Bi(Pb)2223 sintered bulks up to 115 K

Enhancement of Tc was attempted for Bi(Pb)2223 sintered bulks by optimizations of starting cation composition and post-annealing conditions. Tc was enhanced from 110.4 K to 111.4 K after post-annealing at ∼700 deg. C in 1%O2. Additional high temperature annealing at ∼830 deg. C in air largely improved crystallinity of Bi(Pb)2223 and high Tc up to 114.3 K was achieved. Increases in the c-axis length indicated that the enhancement of Tc is possibly due to changes in cation composition towards the stoichiometric one. An as-synthesized Bi(Pb)2223 bulks starting from Sr-rich compositions showed slightly high Tc of 110.8 K, suggesting suppression of partial substitution of Ca and/or Bi for the Sr-site. In addition, Bi-rich starting composition resulted in decreases of secondary phases without suppression of Tc. High temperature post annealing in air performed for these Sr-rich or Bi-rich bulks also improved Tc's up to 114.4 and 114.8 K, respectively