Superconductivity Measurements of (Hg,Tl)-1223 Compound Prepared in Capsule

Abstract

       In this paper, investigations were carried out on the effects of simultaneous partial substitution of Tl at the Hg site on the physical properties of an Hg_1-xTl_xBa₂Ca₂Cu₃O_8+δ cuprate superconductor with x= 0, 0.1, 0.2, 0.3 and 0.4. Two steps of the solid state reaction method were used to prepare samples in capsule. The results showed that the optimum sintering temperature was equal to 850 ^ᵒC and the sintering time was equal to 20 h for the prepared samples.  

    The best conditions for constitution and stabilization of the high T_c phase-1223 were obtained by investigating the effects of Tl substitution on Hg site and oxygen content (δ) on the superconducting properties.

         Structural investigation revealed that all the samples have a tetragonal structure with two phases, namely an Hg-1223 high T_c phase as a main phase and an Hg-1212 low T_c phase. Besides, some impurity phases like CuO and CaHgO₂ were found. The increase of Tl content in Hg_1-xTl_xBa₂Ca₂Cu₃O_8+δ compound from 0 to 0.4 caused a change in the lattice parameter, density of the unit cell (ρ_m), and c/a values.

        HgBa₂Ca₂Cu₃O_8+δ compound exhibited a critical transition temperature that is equal to 115 K. On the other side, the results showed that the highest T_c was 119 K for Hg_0.8Tl_0.2 Ba₂Ca₂Cu₃O_8+δ. The oxygen content (δ= 0.46) was expected to be the optimum hole doping for Hg_0.8Tl_0.2 Ba₂Ca₂Cu₃O_8+δ compound, which  means in our opinion that  δ plays a remarkable role in the assessment of T_c.