AN EFFICIENT AND REPRODUCIBLE APPROACH FOR ATTAINING SUPERCONDUCTIVITY AT 128-K IN TL2BA2CA2CU3O10-DELTA

We report an efficient, and highly reproducible, method for the preparation of almost single phase Tl-2223 material, which is characterized by high-temperature superconductivity with T(cmidpoint) = 128 K and T(czero) = 126 K as measured by electrical resistivity, and a diamagnetic onset temperature [T(cmag)] of 128 K as measured by AC susceptibility. This procedure involves synthesizing a material with nominal stoichiometry Tl1.6Ba2Ca2.4Cu3O10-sigma, which was sintered at 910-degrees-C for 3 h, annealed at 750-degrees-C (10 days) in an evacuated quartz tube, and finally annealed at 600-degrees-C (2 h) in a 0.2% oxygen/nitrogen gas mixture. Based on these results, it appears that the optimization of the hole concentration in Tl-2223, achieved here by controlling the oxidizing/reducing power of the annealing atmosphere, appears to be crucially important in attaining such a high transition temperature.