Effect of the partial replacement of Ca by alkaline element Na on Tl-1223 superconductor

Abstract

We have investigated the effect of Na substitution at Ca sites on the lattice parameters, electrical resistivity, magnetic susceptibility and thermopower coefficient for TlBa2Ca2-xNaxCu3O9-δ; with 0 ⩽ x ⩽ 0.4. The lattice parameters elongate with increasing the Na-content. A little enhancement in the superconducting transition temperature Tc has been observed as x increases from 0 to 0.05 and then it depresses gradually for x > 0.05. This observation was attributed to the fact that Na has converted the Tl- 1223 phase from over-doped regime to under-doped regime which is in conformity with the thermopower results, that found to change from negative (over-doped regime) to positive (under-doped regime). The inter-grain critical current density as function of Na has been also reported from ac magnetic susceptibility measurements.