Contributions from Inter-grain Boundaries to the Magneto-resistive Effect in Polycrystalline High-T C 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 Bi1.8Pb0.3Sr1.9Ca2Cu3O (x) (BSCCO) and YBa2Cu3O7-delta (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 only, while standard measurements of R(T) dependences in magnetic 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.