Abstract
X-ray pair distribution function (PDF) and Extended X-ray absorption fine structure (EXAFS) measurements were carried out on two Fe-based systems BaFe2As2 and LiFeAs to study mainly on the local structures of their FeAs planes. For the former system exhibiting the tetragonal (space group I4/mmm)-orthorhombic (Fmmm) structural phase transition at temperature TS ∼140 K, we show the T dependent characteristics of the local distortion from room temperature to the low temperature Fmmm phase, which support the existence of another local orthorhombic phase (I2mm) [Cantoni et al.: Adv. Mater. 27 (2015) 2715] at 300 K. We show the magnitudes of the local Fe atom shifts from their average Fe sites in these phases as the important information on what roles the lattice distortion has in the arguments on various physical properties of FeAs planes. For LiFeAs with the superconducting transition at ∼18 K but no structural transition, a small distortion has been found below 200 K.
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