Alkali-metal Li and 1,3-diaminopropane intercalated superconductor Lix(C3H10N2)yFe2Se2 with Tc～39 K

A new FeSe-based superconductor Lix(C3H10N2)yFe2Se2 (C3H10N2 refers to 1,3-diaminopropane) was successfully synthesized via the two-step method. This new material belongs to a tetragonal system and has a superconducting transition temperature (Tc) of 35 K. After annealing at 125 °C for 12 h, the crystal structure of this sample remained constant, but the Tc suddenly moved to 39 K, as confirmed by the powder X-ray diffraction and the magnetic susceptibility, respectively. Before and after annealing, the lattice constants a and b changed within 0.3 %, and the changes in c were slightly larger than 1 %. Therefore, it can be inferred that the evident change in Tc between as-synthesized and annealed samples should be attributed to a rearrangement and more homogeneous distribution of the intercalated guests.