Thallium-based cuprate superconductors doped with rare earth oxides

Precursor materials for superconductors with nominal starting compositions of (Tl0.6Pb0.5)(Ba0.2Sr0.8)2(Ca, RE)2Cu3Oy (RE: Y, La, Pr, Sm, Dy) were made via the evaporation of aqueous strontium–barium–calcium–copper– nitrate solutions followed by calcination at 900 ◦C in air. The stoichiometric amounts of the doping oxides were added by co-attrition. Sintering of the specimens was carried out inside a silver foil under flowing oxygen at 925 ◦C for 12 min and at 910 ◦C for 10 h. High quality Tl-1223 and Tl-1212 materials with well connected grains and Tc(0) values between 75 and 115 K were produced. The DeltaT(90−10%) values ranged from 2 to 18 K. Bulk phase jc-values between 40 and 1400 A cm−2 were obtained. Annealing improved the critical current densities. Two-step transitions were generally observed.