The electrical conductivity anisotropy of the σ-bands is calculated for the (Mg,Sc)B 2 system using a virtual crystal model. Our results reveal that anisotropy drops with relatively little scandium content (< 30%); this behaviour coincides with the lowering of T c and the reduction of the Kohn anomaly. This anisotropy loss is also found in the Al and C doped systems. In this work it is argued that the anisotropy, or 2D-character, of the σ-bands is an important parameter for the understanding of the high T c found in MgB 2 .

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