LIMITING FACTORS FOR CRITICAL-CURRENT DENSITIES IN BI2SR2CA2CU3O10-AGCOMPOSITE SUPERCONDUCTING TAPES AT ELEVATED-TEMPERATURES

Detailed measurements of I-V curves at 4.2, 65, and 77 K as a function of applied magnetic field for two Bi (2:2:2:3)/Ag tapes, having criti cal current densities J(c) of approximately 1 and approximately 2 X 10 (4) A/CM2 (at 77 K and 0 T), revealed that (1) the primary limiting fa ctor for the transport critical current densities in these tapes is th e presence of a large fraction of weak and/or nonsuperconducting grain boundaries; (2) the observed dissipative voltages are due, however, m ostly to the motion of the magnetic vortices in the grains; and (3) th e E-J curves are well described by an expression, E approximately exp[ -(J0/J)mu], rather than the commonly used power law, i.e., E approxima tely J(n), where mu, J0, and n are constants.