Electrochemical Synthesis of Ethyl-Substituted Alkylammonium-Intercalated β-FeSe Superconductors with T c up to 44 K

The intercalation of organic cations into superconducting iron selenide can significantly enhance the critical temperature (Tc). We investigated the electrochemical intercalation of ethyltrimethylammonium (ETMA+) and diethyldimethylammonium (DEDMA+) cations into β-FeSe, and their influence on the superconducting properties. High-resolution powder X-ray diffraction and pair distribution function analyses reveal a ThCr2Si2-type structure for both (ETMA)0.4Fe2Se2 and (DEDMA)0.4Fe2Se2, while the detailed structures of the organic interlayer remain elusive. The compounds are type-II superconductors with bulk superconductivity up to Tc = 44 K, supporting the correlation between interlayer spacing and superconductivity in FeSe intercalates.