The Role of Tl Substitution on Superconducting Properties for Hg-1223 System

Abstract

High temperature superconductors with a nominal composition Hg1-xTlxBa2Ca2Cu3O8+δ for (0<x<0.4) were prepared by two-step solid state reaction in air. The effect of the substitution of Tl for Hg, oxygen content (δ) and sintering time (20-200h) on the Hg-12223 superconductivity system has been investigated to obtain the optimum conditions for the formation and stabilization of the high critical temperature (Tc).The results showed that the optimum sintering temperature for the prepared samples was equal to 880 °C, whereas the sintering time is equal to 100 h.The quantity of the element content for Hg1-xTlxBa2Ca2Cu3O8+δ system were carried out using x-ray fluorescence (XRF). X-ray diffraction (XRD) analysis showed a tetragonal structure with a high Tc phases (1223) as a dominant phase and low Tc phase (1212) addition to exist of some impurity phases for all samples. It was found that the change of the Tl concentrations of prepared samples produced a change in the lattice parameters, density ρm and c/a ratio. The highest Tc for HgBa2Ca2Cu3O8+δ composition was 118 K. The results for the doped samples, represented highest Tc equal to 124 K for Hg1-xTlx Ba2Ca2Cu3O8+δ sample with x=0.4.The oxygen content was not systematic changed but it played a great role in the evaluation of Tc.