  The Phase diagram of SmFeAsO1-xFx in terms of x is exhibited in this study.
SmFeAsO1-xFx from x = 0 to x = 0.3 were prepared by low temperature sintering
with slow cooling. The low temperature sintering suppresses the formation of
the amorphous FeAs, which is inevitably produced as an impurity by using high
temperature sintering. Moreover, slow cooling is effective to obtain the high
fluorine concentration. The compositional change from feedstock composition is
quite small after this synthesis. We can reproducibly observe a record
superconducting transition for an iron based superconductor at 58.1 K. This
achievement of a high superconducting transition is due to the success in a
large amount of fluorine substitution. A shrinking of the a lattice parameter
caused by fluorine substitution is observed and the substitutional rate of
fluorine changes at x =0.16.
