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.
@article{arxiv.1303.1309,
title = {{\alpha}-FeAs-free SmFeAsO1-xFx by low temperature sintering with slow cooling},
author = {Masaya Fujioka and Saleem James Denholme and Toshinori Ozaki and Hiroyuki Okazaki and Keita Deguchi and Satoshi Demura and Hiroshi Hara and Tohru Watanabe and Hiroyuki Takeya and Takahide Yamaguchi and Hiroaki Kumakura and Yoshihiko Takano},
journal= {arXiv preprint arXiv:1303.1309},
year = {2015}
}