Synthesis and microstructural studies ofiron oxypnictide LaO 1-xFxFeAs superconductors

Abstract

We report on the synthesis and structural/microstructural studies of iron-based fluorine doped LaOFeAs superconductors. We have successfully synthesized fluorine doped superconducting LaO1-xFxFeAs materials by choosing lower temperature (∼1150 °C) and longer synthesis duration (∼60h) as compared to the standard values of these employed in the pioneering first contribution (Kamihara et al 2008 J.Am.Chem.Soc. 130 3296). A decrease of lattice parameters, as determined by x-ray diffraction, confirms the substitution of fluorine. The superconducting transition temperature is 27.5K which is observed at a doping level of x = 0.2. This superconducting material LaO1-xFxFeAs exhibits interesting microstructural characteristics. These relate to the existence of another structural phase, besides the standard phase, having c parameters of ∼12.67. This suggests the existence of a modulated structure, similar to the cuprates, in these new oxypnictides. This phase may have new impact on this new high-TC family. © 2009 IOP Publishing Ltd.