The Local Structure of the BiS2 Layer in RE(O,F)BiS2 Determined by In-Plane Polarized X-ray Absorption Measurements

We have investigated the local structure of BiS2-based layered materials by Bi L3-edge extended X-ray absorption fine (EXAFS) measurements performed on single crystal samples with polarization beam parallel to BiS2 plane. The results confirm highly instable nature layer, characterized ferroelectric like distortions. distortion amplitude, determined separation between two in-plane (Bi-S1) bonds, is found be highest in LaO0.77F0.23BiS2 ΔR∼0.26 Å and lowest NdO0.71F0.29BiS2 ΔR∼0.13 Å. Among systems intrinsic doping, CeOBiS2 shows smaller (ΔR∼0.15 Å) than PrOBiS2 (ΔR∼0.18 while appears for EuFBiS2 revealing ΔR∼0.22 It that amplitude controlled RE(O,F) spacer layer RE(O,F)BiS2 structure. near edge (XANES) spectra, probing geometry, a spectral weight transfer evolves systematically BiS2-layer. provide quantitative distortions BiS2-layer direct implication physical properties these materials.