Weak links in Pb-doped BiSrCaCuO ceramic superconductors

Abstract

The dependence of the resistive transition curve R( T) on measuring current and magnetic field along with AC and DC magnetic susceptibility χ( T) has been measured on ceramic superconductors of the nominal composition Bi 0.7Pb 0.3SrCaCu 1.8O x to elucidate the nature of weak intergranular links in the samples. These wear links are shown to be responsible for pronounced current-dependent resistive tails analogous to those reported for YBaCuO [1:2:3] ceramics. The R( T) curves can be interpreted in terms of percolative conduction in a multiphase system with superconducting regions coupled via nonsuperconducting barriers. External magnetic fields below 0.1 mT are shown to be sufficient for partial decoupling of the superconducting grains. A possible role of the Pb atoms in the formation of weak links resulting in a suppression of the transport critical current density J c is discussed.