Enhancement of the intergranular superconducting properties in Bi 2Sr 2CaCu 2O 8 with Li additions

Abstract

The superconducting properties of Li-doped Bi 2Sr 2CaCu 2O 8 compounds, with nominal composition (Bi 2Sr 2CaCu 2O 8) 1− x Li x (0⩽ x⩽0.55), have been investigated by means of measurements of AC and DC magnetic susceptibility (χ AC, χ DC), electrical resistivity, X-ray diffraction, and metallographic analysis. These measurements revealed that the superconducting transition temperature T c increased gradually with the Li concentration x, and that the changes in χ AC and χ DC due to the onset of superconductivity increased as well. The real and imaginary components of χ AC versus T data revealed that a second transition appeared below the onset of superconductivity at T c, possibly due to the weak superconducting links that make up the intergranular regions. This second transition is strongly dependent on the applied magnetic field H, and it shifts towards higher temperatures with x. The maximum T c's of the intra- and intergrain regions, maximum χ AC and χ DC signals and maximum intergranular Bean Model critical current density occur for the compound with x = 0.3. Li addition enhances the superconducting properties of the weak intergranular links, making these regions more homogeneous and less sensitive to magnetic fields.