Tuning the interlayer spacing in intercalated FeSe-based superconductors through mixed solvent

Recently, the exploration of novel intercalated FeSe-based superconductors through the wet chemical reactions has been a focal point in condensed matter physics. Here, we present the successful synthesis of two FeSe derivatives, namely Li0.34Se0.05(EG)0.14FeSe and Li0.21Se0.05(EG)0.26FeSe, whose c-axis lattice parameters are 9.93 Å and 13.85 Å, respectively, using the solvothermal ion-exchange technique. The interlayer spacing of the two FeSe derivatives can be tuned by the change of mixed solvent during the synthesis process. The resistivity and magnetic susceptibility measurement results show that their superconducting transition temperatures (Tc) are both about 30 K. Interestingly, the Tc values are found to be independent of the interlayer spacing of the FeSe layer. Compared with the pristine FeSe single crystal, X-ray photoelectron spectroscopy results display a decrease of the Fe valence, indicating that the enhancement in Tc may be caused by an electron doping effect. Our research provides valuable insights into the intercalation of FeSe-based superconductors and offers new possibilities for exploring novel intercalated materials within the field of superconductivity.