Improving Superconducting Characteristics of Tl-Sr-Ca-Cu-O by Doping with Pb and/or Rare-Earth Elements

Abstract

We have investigated the effects of doping Pb and/or rare-earth elements on the T _c of Tl-Sr-Ca-Cu-O. Depending on the amount of Pb doped, at least two superconducting phases were formed: the 1223 and 1212 phase having a T _c of 100 K and 60 K, respectively. The 1223 phase is stabilized by doping and increased in volume by annealing at 550°C. In the case of the rare-earth-doped one, the 1212 phase is stabilized and has a T _c of about 90 K. We also investigated the case of samples doped with both Pb and rare-earth elements. A nominal composition of Tl_0.7Pb_0.3La_0.3SrCaCu_1.8O _y has a T _c of above 100 K, which is the highest of materials with 2-CuO₂ layers.