Abstract
Current transport in polycrystalline magnesium diboride is highly non-uniform(percolative) due to the presence of secondary phases and also due to the intrinsicanisotropy of the material. The influence of secondary phases on the transport properties ofMgB2 was investigated. Bulk samples were prepared from a mixture ofMgB2 and MgO powders by the ex situ technique in order to vary the MgO content systematically.The samples were characterized by resistive and magnetization measurements. The reducedMgB2 fraction is modeled by a reduced effective cross section (connectivity), which wasassessed directly by the experiments. The presence of MgO also increases thepercolation threshold, which reduces the zero resistivity (or irreversibility) field.
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