Effect of Li addition on the properties of Bi-based superconductors

The effect of Li addition on the formation and properties of Pb containing Bi-based superconductors has been studied. Three successive thermal sintering cycles have been applied to the oxides adjusted for the nominal composition, Bi_1.6Pb_0.4Sr₂CaCu₂O_8+d. Eight different samples having Li₂CO₃ from 0.0 up to 3.0 weight% have been synthesized. X-ray diffraction patterns, resistivity-temperature behaviors and differential thermal analysis of the samples have been examined. Li₂CO₃ addition at 650 °C decreases the fraction of (Bi,Pb)-2212 and increases that of Ca₂PbO₄. The normal state resistances of the samples increase, the onset T_c values decrease and the lattice parameters almost remain same with Li₂CO₃ addition. Li₂CO₃ addition up to 3.0 wt% decreases the melting temperature of (Bi,Pb)-2212 phase by about 50°C inducing a liquid phase at about 750 °C. Our observations suggest that the high T_c phase, (Bi,Pb)-2223 may be formed at about 750-800 °C using the precursors, (Bi,Pb)-2212 and Ca₂PbO₄ doped with Li₂CO₃.