Synthesis of a new alkali metal-organic solvent intercalated iron selenide superconductor with Tc 45 K

We report on a new iron selenide superconductor with a Tc onset of 45 K and the nominal composition Lix(C5H5N)yFe2−zSe2, synthesized via intercalation of dissolved alkaline metal in anhydrous pyridine at room temperature. This superconductor exhibits a broad transition, reaching zero resistance at 10 K. Magnetization measurements reveal a superconducting shielding fraction of approximately 30%. Analogous phases intercalated with Na, K and Rb were also synthesized and characterized. The superconducting transition temperature of Lix(C5H5N)yFe2−zSe2 is clearly enhanced in comparison to those of the known superconductors FeSe0.98 (Tc ∼ 8 K) and AxFe2−ySe2 (Tc ∼ 27-32 K) and is in close agreement with critical temperatures recently reported for Lix(NH3)yFe2−zSe2. Post-annealing of intercalated material (Lix(C5H5N)yFe2−zSe2) at elevated temperatures drastically enlarges the c-parameter of the unit cell (∼44%) and increases the superconducting shielding fraction to nearly 100%. Our findings indicate a new synthesis route leading to possibly even higher critical temperatures for materials in this class: by intercalation of organic compounds between Fe-Se layers.