Effect of Ru substitution on atomic displacements in the layered SmFe_{1−x}Ru_{x}AsO_{0.85}F_{0.15} superconductor

The effect of Ru substitution on the local structure of layered SmFe1−xRuxAsO0.85F0.15 superconductor has been studied by As K- and Sm L3-edge x-ray-absorption spectroscopy. The extended x-ray-absorption fine-structure measurements reveal distinct Fe-As and Ru-As bond lengths in the Ru substituted samples with the latter being ∼0.03 Å longer. Local disorder induced by the Ru substitution is mainly confined to the FeAs layer while the SmO spacer layer sustains a relative order, consistent with the x-ray-absorption near-edge structure spectra. The results suggest that, in addition to the order/disorder in the active FeAs layer, its coupling to the rare-earth–oxygen spacer layer needs to be considered for describing the electronic properties of these layered superconductors.