ENHANCEMENT OF CRITICAL CURRENTS IN BULK AND AG-SHEATHED BI(PB)-2223 SUPERCONDUCTORS

The superconducting properties of the Bi(Pb)-2223 phase have been optimized. Prolonged annealing of course powder raised j(c) in bulk samples to as high as 1100 Acm-2 at 77 K. The temperature dependence was studied between 96 and 4.2 K whereby j(c) rose gradually from 120 to 2100 Acm-2. T(c) dropped from 107 K to 64 K in magnetic fields up to 4 T but decreased by only 1 K/T in higher fields. A tape prepared by rolling and subsequent annealing of Ag tubes containing Bi(Pb)-2223 powder exhibited a j(c) of 1700 Acm-2 at 77 K and 11000 Acm-2 at 4.2 K. The latter j(c) dropped to 3000 Acm-2 in a magnetic field of 0.25 T, but it was still 1200 Acm-2 in a 10 T field. A tape fabricated by pressing a drawn and annealed wire proved to be less sensitive to low magnetic fields.