Fe–As Bond-Dynamics Revealed from the Arsenic K-Edge EXAFS Studies of NdFeAsO1?x F x Iron-Pnictide Superconductors

Arsenic K-edge extended x-ray absorption fine structure (EXAFS) spectroscopy results of the NdFeAsO_1?x F _x (x=0 and 0.12) system at room temperature and 12 K are presented. The Fe–As bond seems to be hardly affected by doping and temperature. However, a careful analysis of the temperature dependence of the Fe–As bond mean-square relative displacements reveals a hardening of the Fe–As bond force constant in the superconductor compared to the NdFeAsO, revealing the distinct local lattice dynamics in the active iron-arsenic layer in governing the superconducting properties.