M. Eisterer, J. Emhofer, S. Sorta, M. Zehetmayer, H. W. Weber:
"Connectivity and critical currents in polycrystalline MgB2";
Superconductor Science and Technology,
Current transport in polycrystalline magnesium diboride is highly non-uniform (percolative) due to the presence of secondary phases and also due to the instrinsic anisotropy of the material. The influence of secondary phases on the transport properties of MgB2 was investigated. Bulk samples were prepared from a mixture of MgB2 and MgO powders by the <i> ex </i> situ technique in order to vary the MgO content systematically. The samples were characterized by resistive and magnetization measurements. The reduced MgB2 fraction is modeled by a reduced effective cross section (connectivity), which was assessed directly by the experiments. The presence of MgO also increases the percolation threshold, which reduces the zero resistivity (or irreversibility) field.
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