Pb substitution effect on the normal and superconductivity states transport of polycrystalline MgB_2

摘要

A series of samples of Mg_(1-x)Pb_xB_2 were synthesized by the conventional solid state reaction method. Its temperature dependence of resistivity was studied from the zero resistivity temperature T_c up to 300 K. In order to more understand the main reason of the decreases of T_c, we analyse the resistivity versus temperature data in the normal state using Bloch-Grimeisen formula. The Debye temperature, θ_D, has been extracted from the fits. Θ_D is seen to decrease with the lead substitution from 1280 K to 835 K. Using θ_D and T_c, the electron-phonon interaction parameter X, has been given by McMillan equation. The values of λ increase from 0.70 to 0.84 respectively for x = 0 % and x = 1 % sample. The decrease in T_c is argued mainly by the decrease in the density of states at the Fermi level N(E_F) with Pb concentration than the decrease in θ_D.