Synthesis of Tl-Ba-Ca-Cu-O Superconducting Thin Films by Sequential Evaporation and Annealing in the Absence of An Additional Thallium Source

Although Tl-based superconductors show higher critical temperatures than other compounds, they suffer some disadvantages, such as surface roughness, non-uniform chemical composition, and the need for excess Tl from a separate source during post-deposition annealing. This paper reports a post-deposition annealing process (in the absence of a separate Tl source) of sequentially deposited metallic layers of Tl:Ba:Ca:Cu with excess amount of thallium in the multilayer. The films show uniform chemical composition and smooth surfaces. Critical temperatures as high as 101 K and critical current densities as high as 1.5 × 10⁴ A/ cm² at 77 K in zero magnetic field have been achieved.