{\alpha}-FeAs-free SmFeAsO1-xFx by low temperature sintering with slow cooling

TL;DR

This study demonstrates that low temperature sintering combined with slow cooling effectively produces amorphous-FeAs-free SmFeAsO1-xFx with high fluorine content and enhanced superconductivity at 57.8 K.

Contribution

It introduces a novel low temperature sintering and slow cooling method to synthesize high-quality SmFeAsO1-xFx superconductors with high fluorine homogeneity.

Findings

Superconductivity at 57.8 K achieved.

High superconducting volume fraction of 96%.

Fluorine substitution occurs during cooling, not just at maximum temperature.

Abstract

We obtained amorphous-FeAs-free SmFeAsO1-xFx using a low temperature sintering with slow cooling. SmFeAsO1-xFx is sintered at 980 {\deg}C for 40 hours and cooled slowly down to 600 {\deg}C. The low temperature sintering suppresses the formation of amorphous FeAs, and the slow cooling introduces much fluorine into SmFeAsO1-xFx. The superconductivity of this sample appears at 57.8 K and the superconducting volume fraction reaches 96 %. To study the change of fluorine concentration during the cooling process, samples are quenched by water at 950 {\deg}C, 900 {\deg}C, 850 {\deg}C, 800 {\deg}C, 750 {\deg}C and 700 {\deg}C. It is found that fluorine is substituted not only at the maximum heating temperature but also during the cooling process. The low temperature sintering with slow cooling is very effective to obtain a homogeneous SmFeAsO1-xFx with high fluorine concentration.