Synthesis and electron microscopic characterisation of Tl(Bi )-Sr-Ca-Cu-O high temperature superconductort

Abstract

The HTSC materials of Tl(Bi)-Sr-Ca-Cu-O system, corresponding to nominal compositions TI_2-XBi_XSr₂Ca₂Cu₃O₁₀(<em>x=</em>0.2<em>, </em>0.4, 0.6 and 1.0) and with Tc in the range ~77 to ~106 K, have been synthesized. The electron microscopic explorations of the synthesized HTSC materials show curious structural characteristics. The transmission electron microscopic (TEM) investigations have revealed the presence of a new disordered superstructure (a ≈ 4.2 Ǻ, C ≈ 15.26 Ǻ). The origin of disorder is thought to be germane to the presence of lone pairs on Bi³⁺. It has also been suggested that substitution of Bi³⁺ at TI site in TI-Sr-Ca-Cu-O system optimises the carrier concentration (hole) leading to increase in Tc.