Boosting the superconducting properties of Fe(Se, Te) through hexagonal phase manipulation

Halogen doped Fe(Se, Te) superconducting materials were successfully synthesized through the eutectic transformation method. Both the distribution and morphology of the secondary hexagonal phase were tuned accordingly by substituting halogen elements. The morphology of the hexagonal phase was transformed from plate-like lamellar to agglomerated dots or bulk precipitates as the doping elements changed from F to Cl and Br. Moreover, the flux pinning mechanism, which represents the ability of materials to trap the penetrating magnetic field, was observed to change from Δκ to point pinning when doped by elements with heavier atomic mass. As a result, tremendous optimization of the critical current, upper critical field, and thermally activated flux flow activation energy were achieved in the as-prepared samples, with a specific value of 7 times, 2 times, and 3 times, respectively, in FeSe_0.45Te_0.5F_0.05 compared with the values for the undoped sample. Our results reveal that the light-halogen element doping is a promising way to optimize the superconductivities in the Fe(Se, Te) systems and inspire us to manipulate the morphology of secondary phase to boost the superconductivities in iron-based superconductors.