Enhancement in critical current density of Bi-Pb-Sr-Ca-Cu-O tapes by thermomechanical processing: Cold rolling versus uniaxial pressing

Critical current densities up to 24 000 A/cm2 (Ic∼23.6 A) at 77 K, zero field, have been measured in short tape samples of silver-sheathed Bi-Pb-Sr-Ca-Cu-O superconductors made by the powder-in-tube technique. These samples carried 3000 A/cm2 at 1 T and 1000 A/cm2 at 2 T, also at liquid-nitrogen temperature. A repeated cold work (rolling and pressing) together with an intermediate heat treatment were required to achieve these properties. Without the pressing, tapes were made with Jc’s as high as 15 000 A/cm2 at 77 K, zero field. The role of uniaxial pressing as compared to rolling is discussed and its implications to long length conductor fabrication described.