TlxBa2Ca3Cu4Oysuperconductors from coprecipitated oxalate precursors

Precursor material for Tl-Ba-Ca-Cu-O superconductors was prepared by coprecipitation of the cations as oxalates. Following calcination at 600°C, the powders were attrited, then uniaxially compacted at 7000 bar and converted into superconducting ceramics by sintering in the temperature range of 880°C to 915°C. The thallium content and the Tc(0) depended strongly on the sintering conditions. Best results were obtained for samples with the composition Tl1.4Ba2Ca3Cu4O11.4yielding superconductors with a Tc(0) of 118 K and a critical current density of 19.4 A cm−2at 77 K.