Temperature dependent local atomic displacements in Ru substituted SmFe1-xRuxAsO0.F-85(0).(15) superconductors

The local structure of SmFe1-xRuxAsO0.F-85(0.15) (x = 0.0, 0.05, 0.25 and 0.5) superconductors has been investigated by temperature dependent As K-edge extended x-ray absorption fine structure analysis. The effect of Ru substitution remains confined to the iron-arsenide layer but neither the static disorder nor the Fe-As bond strength suffers any change for x <= 0.25. With further Ru substitution the static disorder increases while the Fe-As bond strength remains unchanged. Also, the Ru-As distance (similar to 2.42 angstrom), different from the Fe-As distance (similar to 2.39 angstrom), does not show any change in its force constant with Ru substitution. These observations suggest that the SmFe1-xRuxAsO0.F-85(0).(15) system breaks down into coexisting local electronic phases on isoelectric substitution in the active FeAs layer.