Random alloy-like local structure of Fe(Se, S)1−xTexsuperconductors revealed by extended x-ray absorption fine structure

The local structure of Fe(Se, S)1−xTex ternary (11-type) chalcogenides has been studied by temperature dependent Fe K-edge extended x-ray absorption fine structure measurements. We find that the Fe–Se and Fe–Te distances in ternary FeSe1−xTex are closer to the respective distances in the binary systems, revealing significant divergence of the local structure from the average one. The mean square relative displacements show a systematic change with Te content, consistent with bond relaxation in the inhomogeneous ternary phases. Also, the Fe–Te and Fe–S distances in the FeS0.2Te0.8 ternary system are found to be different in the crystallographically homogeneous structure. The observed features are characteristic of ternary random alloys, suggesting that a proper consideration should be given to the atomic distribution for describing the complex electronic structure of these multi-band Fe-based chalcogenides.