bSchool of Applied Physics,

Superconducting properties of Tl1-xPbxSr1.8Sb0.2CaCu2O7 (x = 0.1 – 0.6) ceramics prepared using solid-state synthesis have been investigated. Tl1-xPbxSr1.8Sb0.2CaCu2O7 (x = 0.1 – 0.5) showed metallic normal state behavior and an increase in Tc zero from 26 K at x = 0.1 to a maximum value of 80 K at x = 0.5. Further substitution of Pb to x = 0.6 caused a decrease in Tc zero to 27 K. The transport critical current density, Jc measured in zero magnetic field for Tl1-xPbxSr1.8Sb0.2CaCu2O7 (x = 0.2 – 0.4) between 20 K and 80 K was determined by the four-point probe measurement using the 1µVcm-1 criterion. Jc increases when the temperature is reduced for all samples (x = 0.2 – 0.4). The results of the electrical measurements and powder X-ray diffractions analysis are presented. The significance of each elemental substitution at different atomic sites are suggested. Effects of Pb and Sb substitution are discussed in terms of average Cu valence. Behavior of transport critical current density Jc with temperature was explained using a self-field approximation