Influences of fluorine doping on the superconducting properties of β-FeSe

Fluorine doping Fe1.2Se polycrystalline were prepared by solid-state sintering method. The influences of fluorine doping content and sintering temperatures on phase composition, lattice parameters, microstructure as well as superconducting properties were discussed in detail. It was found that fluorine doping could effectively reduce the content of non-superconducting hexagonal δ-FeSe phase. Besides, the content of hexagonal δ-FeSe phase and grain size of superconducting tetragonal β-FeSe phase were decreased with the sintering temperature increasing. Scanning electron microscopes (SEM) images indicated that the morphology of β-FeSe phase was a typical lamellar structure with the small particles of hexagonal δ-FeSe phase. Meanwhile, a higher critical temperature Tc of 8.3 K and larger shield volume fraction were obtained with high sintering temperature of 950 °C and proper F doping content.