Hydrothermal synthesis of tetragonal FeS: Dome-shaped superconductivity vs Fe:S actual molar ratios.

We successfully synthesized tetragonal FeS with various Fe:S molar ratios using a hydrothermal method, and the EDS and XRF results confirmed that FeS exhibits superconductivity within the Fe and S element ratio range of 1.155–1.274, rather than a strict stoichiometric ratio. The reaction temperature can not only play a crucial role in determining the purity of the obtained FeS phase but also significantly alter its micromorphology. Significantly, by analyzing the relationship between the Fe:S actual molar ratio and T_c as well as the Fe:S actual molar ratio and unit cell volume, FeS exhibits dome-shaped superconductivity and shows a negative correlation with T_c and chemical pressure. Furthermore, considering the correlation between anion height (h_anion) and T_c, T_c reaches the maximum value of 4.53 K for h_anion ≈ 1.28 Å, a behavior distinct from that of observed in Fe-pnictide superconductors. In short, our experimental results provide a unique perspective to deepen our understanding of FeS superconductors. [ABSTRACT FROM AUTHOR]