Effect of electron and hole doping on the superconducting and normal state properties of MgB2

The variation of TC in MgB2 has been systematically investigated for monovalent cation substitution in Mg1-xLixB2 and in Mg1-xCuxB2 and simultaneous cation and Carbon substitution in Mg0.80Li0.20B2-xCx and Mg0.95Cu0.05B2-xCx using dc resistivity and ac susceptibility techniques. TC seems to be uniquely determined by the electron count in the sample, being constant at the MgB2 value for electron counts lower than MgB2 but rapidly decreasing for larger electron counts. The Debye temperature extracted from fitting normal state resistivity to the Bloch-Gruneisen formula shows no systematics with TC while the residual resistivity versus TC indicates that interband/intraband scattering is affected by the substitutions.