Contributions from Inter-grain Boundaries to the Magneto-resistive Effect in Polycrystalline High-TC Superconductors. The Underlying Reason of Different Behavior for YBCO and BSCCO Systems

In order to clarify the mechanisms in charge of broadening of resistive transition R ( T ) in magnetic fields of bismuth-based polycrystalline high- T C superconductor (HTSC), a comparative study of Bi 1.8 Pb 0.3 Sr 1.9 Ca 2 Cu 3 O x (BSCCO) and YBa 2 Cu 3 O 7− δ (YBCO) have been performed. Magnetoresistive effects and irreversibility line obtained from magnetic measurements have been studied. It was established that (1) for YBCO, the smooth part of R ( T ) dependence unambiguously corresponds to dissipation in the intergrain boundaries for arbitrary magnetic fields; (2) for polycrystalline BSCCO, the smooth part of R ( T ) dependences correspond to dissipation within intergrain boundary subsystem in the field range H 10 2 Oe reflect the dissipation processes occurring both in intergrain boundary and HTSC grain subsystems; (3) for the high-field range, the contribution from intergrain boundaries of BSCCO can be distinguished from magnetoresistance R ( H ) dependences obtained at high enough current density on textured samples. It is proposed that various magneto-resistive properties of these classical HTSC systems are due comparatively weak pinning in BSCCO.