Phase diagram and oxygen annealing effect of FeTe1−xSex iron-based superconductor

Phase diagrams of as-grown and O2-annealed FeTe1−xSex determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x≥0.15, and weak superconductivity appeared when x≥0.1. Beginning at x=0.5, weak superconductivity was found to evolve into bulk superconductivity. Interestingly, for O2-annealed samples, complete suppression of magnetic order and the occurrence of bulk superconductivity were observed when x≥0.1. We found that O2-annealing induces bulk superconductivity for FeTe1−xSex. Oxygen probably plays a key role in the suppression of the magnetic order and the appearance of bulk superconductivity.