Effect of Ce Substitution on the Properties of Tl-Based Superconductors

Samples with nominal composition (Tl_0.5Pb_0.5)Sr_2-xCe_xCa ₂Cu₃O_y were prepared with x in the range 0 to 0.5, to investigate the role of charge carrier concentration on the superconducting properties of Tl-based materials. The behavior of the normal state resistivity with temperature showed that as x changes from 0 to 0.2, the material moves towards optimally doped state. For higher Ce content the normal state resistivity versus temperature, started deviating from linearity. The onset transition temperature increased gradually by about 6 K as x was increased from 0 to 0.2. The zero resistance transition temperature rapidly decreased for samples with x > 0.2. Furthermore, XRD analysis revealed that Ce enters the structure of both Tl-1223 and Tl1212. These results are discussed in terms of controlling the hole concentration in the CuO₂ planes through Ce⁴⁺ replacement of Sr²⁺.