Phase diagram and superconductivity at 58.1 K in α-FeAs free SmFeAsO1-xFx
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. In addition, the low temperature sintering with slow cooling extends the solid solubility limit of fluorine in SmFeAsO1-xFx up to x = 0.16 in this study.