Doped Tl-1223 superconductors

Doped Tl-1223 superconductors of the composition TlaBibPbcBanSr2-nCa2Cu3Oy (a = 0.47 - 0.68, b = 0, 0.16 and 0.3, c = 0.5, 0.24 and 0, n = 0.2 and 0.4) were prepared from oxidic Ba-Sr-Ca-Cu precursor material. Upon calcination of the tartrate gels, the respective amounts of Tl2O3, PbO and Bi2O3 were added to the oxidic powders by milling. The samples were sintered in silver foil. The specimens consisted predominantely of the Tl-1223 phase with small amounts of Tl-1212 and secondary phases. Tc(0)-values ranged between 116 K and 118 K with transition widths around 1 K. Transport critical current densities up to 1.6 kA cm-2 at 77 K were measured for the as-sintered samples. Texturing was obtained by repressing and resintering of the superconducting material followed by annealing at 750 0C for 50 h in flowing oxygen. The transport critical current densities could be improved up to 7 kA cm-2 by the thermomechanical treatment. Microstructural studies yielded information on the alignment of the superconducting grains, on secondary phases and the porosities. The thermomechanical behaviour was investigated by dilatometric measurements.