Preparation of the Orthorhombic Li_x(C₂H₈N₂)_yFe₂Se₂ Superconductor by Amine Exchange Method

Abstract

A new FeSe-based superconductor Li x (C 2 H 8 N 2 ) y Fe 2 Se 2 with Tc = 30 K was successfully synthesized by substituting ethylenediamine(en) for ammonia molecules in Li x (NH 3 ) y Fe 2 Se 2 . The XRD pattern indicates that the intercalation compound is an orthorhombic structure with lattice parameters a = 3.8517(7)Å, b = 3.9188(7)Å, c = 21.4862(6)Å at room temperature, which is different from the tetrahedral phase Li x (C 2 H 8 N 2 ) y Fe 2 Se 2 with Tc = 45 K synthesized by solvothermal method. Compared with the precursor Li x (NH 3 ) y Fe 2 Se 2 , the Li x (C 2 H 8 N 2 ) y Fe 2 Se 2 underwent a structure transition from tetrahedral to orthorhombic during the amine exchange reaction accompanying by the decrease of Tc, indicating that Tc is influenced by structure.