Homogeneity range of ternary 11-type chalcogenides Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$

The 11-type Fe-chalcogenides belong to the family of Fe-based superconductors. In these compounds, the interstitial Fe is known to strongly influence the magnetic and superconducting properties. Here we present the chemical homogeneity range of ternary compounds Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ based on powder x-ray diffraction, energy dispersive x-ray analysis and magnetization measurements. Our investigations show that the maximum amount of excess Fe in homogeneous Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ decreases with increase in Se substitution for Te. Using our synthesis procedure, single-phase Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$, with $0.5\le x<1$ could not be formed for any amount of excess Fe. Further, the superconducting volume fraction in the material is found to be strongly suppressed by excess Fe.