  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 (1150^0C) and longer synthesis duration (60 hours) as compared to
the standard values of these employed in the pioneering first contribution
[Kamihara et al 2008 J Am Chem Soc 130 3296]. Decrease of lattice parameters as
determined by x-ray diffraction confirm the substitution of fluorine. The
superconducting transition temperature is 27.5 K which is observed at doping
level of x=0.2. This superconducting material LaO1-xFxFeAs exhibits interesting
microstructural characteristic. This relates to the existence of another
structural phase, besides the standard phase, having c parameters of ~12.67A.
This suggests existence of modulated structure, similar to the cuprates, in
these new oxypnictides. This phase may have new impacts on this new high-Tc
family.
