Lattice anomalies in the FeAs₄ tetrahedra of the NdFeAsO_0.85 superconductor that disappear at T_c

¹ Solid State Physics Department, School of Physics, University of Athens - GR-15784 Athens, Greece, EU
² ESRF - BP 220, Grenoble, Cedex 9, F-38043 France, EU
³ Department of Physics, National Technical University of Athens - 157 80 Athens, Greece, EU
⁴ National Laboratory for Superconductivity, Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences - P.O. Box 603, Beijing, China

^a mcalam@phys.uoa.gr

Received: 5 July 2010
Accepted: 24 August 2010

Abstract

High-resolution synchrotron X-ray powder diffraction (SXRPD) was used to study the temperature dependence of the oxygen-deficient NdFeAsO_0.85 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 T_c strongly indicating a connection with superconductivity.