Effects of Cu and other metallic dopings on the superconducting properties of MgB₂

Many efforts have been devoted, after the discovery of superconductivity in MgB₂ [1], to understand the mechanisms of superconductivity in this system and the possible increase of its critical temperature. The aim of this work is to investigate the influence of heteroatoms doping in MgB₂, substitufing Mg and/or B during the classical synthesis of MgB₂. Various elements were tested: mainly Cu and Ca, Sr, Cr, Mn, C and Si, devising various technological expedients when necessary to ensure an actual, even if partial, entrance of the dopants in the MgB₂ lattice. Unfortunately the elements tested so far produced a decrease in T_c or a very small increase: actually Si and C seem to have a slightly positive effect on T_c. The reasons for the observed effects were analysed and tentative explanations offered: in any case some interesting deductions on the nature of superconductivity in MgB₂ were drawn.