DOPED TL-1223 SUPERCONDUCTORS

Doped Tl-1223 superconductors of the composition TlaBibPbcBanSr2-nCa2C u3Oy (a = 0.50 - 0.76, b = 0, 0.16 and 0.3, c = 0.5, 0.24 and 0, n = 0 .15 - 0.4) were prepared from oxidic Ba-Sr-Ca-Cu precursor material. U pon calcination of the tartrate gels or the nitrates, the respective a mounts of Tl2O3, PbO and Bi2O3 were added to the oxidic powders by mil ling. The samples were sintered in silver foil. The specimens consiste d predominantely of the Tl-1223 phase with small amounts of Tl-1212 an d secondary phases. T-c(0)-values ranged between 115 K and 119 K with transition widths around 1 K. Transport critical current densities up to 1.4 kA cm(-2) at 77 K were measured for the as-sintered samples. Te xturing was obtained by repressing and resintering of the superconduct ing material followed by annealing at 750 degrees C for 50 h in flowin g oxygen. The transport critical current densities could be improved u p to 7 kA cm(-2) by the thermomechanical treatment. Microstructural st udies yielded information on the alignment of the superconducting grai ns, on secondary phases and the porosities.