FACTORS SUPPRESSING TRANSPORT CRITICAL-CURRENT IN AG BI2223 TAPES/

The microstructural factors limiting the critical current density J(c) have been investigated for the silver-sheathed Bi2223 tapes prepared by the powder-in-tube technique. In a hierarchy among them, which fact or is the most effective in determining J(c) depends on how extensivel y each of them occurs. The J(c) was found to increase when the volume fraction of 2223 phase increases, suggesting the importance of the con nectivity among 2223 grains. The J(c) also increased with decreasing a mount of residual carbon. The temperature and magnetic field dependenc es of J(c) indicated characteristics of Josephson currents through sup erconducting-normal-superconducting barriers. After a discussion based on the alternative current limiting mechanisms proposed up to now, it is suggested that the homophase grain boundary limits the J(c). (C) 1 996 American Institute of Physics.