Effect of Ru susbstitution on atomic displacements in the layered   SmFe_{1-x}Ru_xAsO_{0.85}F_{0.15} superconductor
  The effect of Ru substitution on the local structure of layered SmFe$_{1-x}$Ru$_x$AsO$_{0.85}$F$_{0.15}$ superconductor has been studied by As $K$- and Sm $L_3$ - edges x-ray-absorption spectroscopy. The extended x-ray-absorption fine-structure measurements reveal distinct Fe-As and Ru-As bondlengths in the Ru substituted samples with the latter being $\sim$0.03 \AA\ 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 active iron-arsenide layer, its coupling to the rare-earth\textminus oxygen spacer layer needs to be considered for describing the electronic properties of these layered superconductors. 
A. Iadecola, B. Joseph, L. Simonelli, L. Maugeri, M. Fratini, A.   Martinelli, A. Palenzona, M. Putti, and N. L. Saini
cond-mat.supr-con cond-mat.mtrl-sci