Uranium-doped thallium-1223 superconductors

The effect of incorporating uranium into thallium-based superconducting samples has been investigated. Oxidic precursor material of the formal stoichiometry (Tl0.6Pb0.5)(Sr0.8Ba0.2)2Ca2Cu3UxOy was prepared by a wet chemical route followed by solid-state reactions. x values of 0.005, 0.01 and 0.02 yielded almost the pure Tl-1223 phase with Tc(0) values of 114 K. For x values of 0.08 and 0.2, considerable amounts of the Tl-1212 phase were found, two-step transitions were observed in the resistance-temperature curves and the Tc(0) values dropped to 107 K and 103 K, respectively. Energy dispersive x-ray analysis indicated that uranium was incorporated into the superconducting crystallites. Concentrations of uranium above x = 0.2 did not result in superconducting material. The introduction of uranium into the tetragonal Tl-1223 phase led to a decrease in the c-axis, but did not affect the a-axis. (author)