Phase diagram and superconductivity at 58.1 K in {\alpha}-FeAs free SmFeAsO1-xFx

TL;DR

This study presents a detailed phase diagram of SmFeAsO1-xFx, demonstrating a record superconducting transition temperature of 58.1 K achieved through optimized low-temperature sintering and fluorine substitution.

Contribution

It introduces a reproducible synthesis method that enhances fluorine incorporation, leading to the highest reported Tc in this class of iron-based superconductors.

Findings

Record superconducting transition temperature of 58.1 K.

Effective suppression of FeAs impurity formation.

Fluorine substitution rate changes at x=0.16.

Abstract

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.