Synthesis, structure and superconductivity of FeS1−xSex (0 ≤ x ≤ 1) solid solution crystals

Abstract

The binary Fe chalcogenides FeSe and FeS are two superconductors which were discovered in recent years and have attracted a lot of attention in physical, chemical and materials research fields. In this work, we have synthesized FeS_1−xSe_x solid solution crystals with the whole x range (0 ≤ x ≤ 1), where the S-rich part (0.1 ≤ x < 0.5) is reported for the first time so far. A hydrothermal route was carried out by de-intercalating K from the K_0.8Fe_1.6(S_1−xSe_x)₂ precursor and FeS_1−xSe_x crystal sheets were thus obtained. Powder X-ray diffraction shows that the tetragonal lattice is maintained from x = 0 to 1 in this solid solution, and the selected area electron diffraction indicates the S/Se mixed occupation without any superstructure. As the Se content x increases, the lattice parameters expand due to the larger radius of the Se anion. Magnetic susceptibility demonstrates that with x ≤ 0.3, FeS_1−xSe_x crystals superconduct with the critical temperature basically unchanged (∼4 K). On the other hand, the Se-rich part of FeS_1−xSe_x crystals (x ≥ 0.6) exhibits an antiferromagnetic transition below 50 K, which could be attributed to the oxygen incorporation during the synthesis. Resistance measurement shows that the nematic order transition which was reported for FeSe in previous studies is absent in FeS_1−xSe_x (x ≤ 0.3) superconductors. This suggests that the superconducting mechanism in FeS-based chalcogenides may differ from that of FeSe.