PROCESSING OF THALLIUM-BASED SUPERCONDUCTING TAPES FOR HIGH-CURRENT DENSITY

Optimum thermomechanical processing conditions have been developed to achieve a high current density in powder-in-tube (PIT) thallium-based (Tl,Pb)-1223 and (Tl,Bi)-1223 tapes. Critical currents in excess of 25 A corresponding to a current density of 20000 A/cm(2) have been achie ved in these tapes at 77 K. Heat treatment and intermediate deformatio n sequences, heating rates, and starting precursor phase assemblages h ave been examined to optimize the current density. A combination of pr ocessing conditions that result in incremental densification, less mic rocracking and liquid formation in the early and final stages of therm omechanical treatment is found to result in the highest current densit ies.