Abstract
High-resolution synchrotron X-ray powder diffraction (SXRPD) was used to study the temperature dependence of the oxygen-deficient NdFeAsO0.85 superconducting compound. By employing a dense temperature sampling we have managed to reveal unnoticed structural modifications that start around ∼180 K, and disappear at the transition temperature. The data show minor changes of the structural characteristics in the Nd-O charge reservoir layer while in the superconducting Fe-As layer the FeAs4 tetrahedron shows gradual modifications below ∼180 K, which suddenly disappear at Tc strongly indicating a connection with superconductivity.