Effect of Nanosized FeF2 Addition on Phase Formation, Microstructure and Critical Temperature of Tl2Ba2CaCu2O8 Superconductor

Abstract

The Tl₂Ba₂CaCu₂O₈ (Tl-2212) phase superconductor with critical temperature 110 K, offers a better phase stability, easier synthesis control and more reproducible superconducting properties than Tl₂Ba₂Ca₂Cu₃O₁₀ (Tl-2223) with critical temperature 125 K, making it more suitable for systematic studies despite its slightly lower critical temperature. To enhance the critical current density, magnetic nanoparticles with size, l between the coherence length, x and the penetration depth, l can be added to the Tl-2212 phase, where the particles act as effective flux pinning centers. In this study, 120 nm antiferromagnetic FeF₂ nanoparticles were added into Tl₂Ba₂Ca₂Cu₂O₈(FeF₂)_x with x = 0 to 0.04 wt.%. The main aim was to investigate the effects of nanosized FeF₂ on the Tl-2212 phase formation and critical temperature. X-ray diffraction (XRD) analysis confirmed that a single Tl-2212 superconducting phase was formed in all FeF₂ added samples. The non-added sample exhibited a superconducting onset critical temperature (T_c-onset) of 108 K, whereas samples with FeF₂ additions of x ≤ 0.03 wt. % retained a relatively high T_c-onset of approximately 100 K, indicating that low FeF₂ concentrations have only a minimal effect on the onset of superconductivity. These results demonstrate that FeF₂ can be incorporated into Tl-2212 without causing significant disruption to phase formation or the critical temperature provided that the doping level is x ≤ 0.03 wt.%. This suggests that careful FeF₂ doping could be a viable addition for optimizing microstructural and textural properties while maintaining high critical temperature.