Electrical transport characteristics of superconducting MgB_2-MgO composite near continuous percolation

摘要

Superconducting MgB_2-MgO composite with about 75% mole concentration of MgO was synthesized in situ by a single-replacement reaction. The resistance versus temperature curve shows that the composite has a high superconducting transition temperature to 38.0 K and metallic transport behavior with low resistivity and highly residual resistance ratio comparable to a pure MgB_2 sample. These characteristics are explained by using the statistical percolation model and a conductivity expression with temperature for the metal-insulator MgB_2 composite is given in this paper. The results indicate that MgB_2 superconductor can tolerance a high content of insulating contamination and this metal-insulator MgB_2-MgO composite can be utilized for the superconducting fault current limiter.