Macroscopically ordered phase separation: A new strategy for improving the superconducting performance in Fe(Se, Te)

Abstract

The phase separation commonly exists in Fe(Se, Te) and damages their superconducting performance. In this paper, we successfully tuned the phase separation in Fe(Se, Te) via adding FeF2 to the raw materials. A macroscopically ordered phase separation which exhibited submillimetre scale striations in width arranged along the c-axis was formed in the FeF2-added Fe(Se, Te), different from the commonly observed flower shape phase separation in FeF2-free Fe(Se, Te). Moreover, the two macroscopical separated phases were identified as FeSe0.6Te0.4 and FeSe0.4Te0.6. The regular phase separation morphology and the fixed phase composition enhanced the flux pinning behavior which induced the appearance of Δκ pinning and deferred the changing from point pinning to surface pinning with the raising temperature. As a result, Fe(Se, Te) with the macroscopically ordered phase separation overwhelms the common phase separation Fe(Se, Te) in Hc2, U0, and Jc. Notably, at 4.2 K, the critical current density Jc reaches 9.3 × 104 A/cm2 in self-field and 1.3 × 104 A/cm2 at 7 T which outclassed the reported values. Besides, the well-defined stoichiometry of the separated phase also lead to a higher Tc of 15.42 K with a narrower transition width of only 0.98 K. Overall, our work reveals the tuning of phase separation in Fe(Se, Te) in terms of phase morphology and stoichiometry, which is a new strategy for improving the superconducting performance in Fe(Se, Te).

Keywords

• Iron-based superconductors
• Fe(Se
• Te)
• Phase separation
• Critical current density
• FeF2 addition