HOT DEFORMATION EFFECTS ON CRITICAL CURRENTS IN (BI,PB)(2)SR2CA2CU3OX SILVER-SHEATHED TAPES

We have subjected fully reacted high-quality pressed silver-sheathed (Bipb)(2)Sr2Ca2Cu3Ox tapes to a hot deformation treatment at various temperatures and times. The critical current density j(c) of these tapes before deformation is about 34 kA/cm(2) in self-field at 77 K. Some dependence exists upon the length of the deformation treatment but the deformation-induced effects can be summarized as follows: The self-field j(c) at 77 K is enhanced to about 42 kA/cm(2), about a 25% increase. The field dependence of j(c) is weakened significantly and thus we still measure about 1000 A/cm(2) at 77 K, 0.5 T (H perpendicular to tape), which is the highest values measured in tapes up to date. Thus even though these tapes do not have the highest self-field j(c) values they mark new standards for j(c) values in high magnetic fields for non-irradiated tapes. At lower measuring temperatures strongly enhanced in field j(c) values are also observed. The irreversibility line appears to be shifted to higher field for both orientations of the tape with respect to the magnetic field. Using transmission electron microscopy we find an enhanced density of basal plane dislocations generated by the deformation at high temperature.