Structural evolution and phase diagram of the superconducting iron selenides Lix(C2H8N2)yFe2Se2(x=0∼0.8)

Abstract

Here we report on the structural and electronic phase diagram of lithium and ethylenediamine intercalated FeSe in a wide range of dopant concentration (x=0∼0.8). Undoped (C2H8N2)yFe2Se2 crystallizes in an orthorhombic phase. With increasing lithium doping, an orthorhombic to tetragonal phase transition occurs at x=0.35, and the superconducting tetragonal phase persists until x=0.5. Meanwhile, the Tc is found dependent strongly on dopant concentration, raising rapidly from 30 K at x=0.35 to 45 K at x=0.5. The crystal structures of Li0.31(3)(C2H8N2)0.52(7)Fe2.03(2)Se2 are determined by using high-resolution neutron diffraction data at 5, 60, 150, and 295 K, respectively. The distortion of the FeSe tetrahedron is enhanced significantly from 150 to 295 K, meanwhile, the normal-state Hall resistivity changes sign from negative to positive in the same temperature range. The dominant hole carrier in electron-doped Li0.5(C2H8N2)yFe2Se2 above 230 K suggests that the temperature-induced structure distortion may lead to a reconstruction of the Fermi surface topology and the appearance of hole pockets.

Source-reported materials — not catalogue approval

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