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

Phase diagrams of as-grown and O$_{2}$-annealed FeTe$_{1-x}$Se$_{x}$ decided by magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the region of $x \quad \ge $ 0.15 and superconductivity appeared at $x \quad \ge $ 0.1. However, bulk superconductivity emerged at only $x$ = 0.5. Interestingly, for O$_{2}$-annealed samples, complete suppression of the magnetic order and bulk superconductivity was observed at $x \quad \ge $ 0.1. We found that O$_{2}$ annealing induces the bulk superconductivity for FeTe$_{1-x}$Se$_{x}$. The O$_{2}$ probably play a key role of a suppression of the magnetic order and appearance of bulk superconductivity.