Electrochemical synthesis and crystal structure of the organic ion intercalated superconductor (TMA)0.5Fe2Se2 with Tc = 43 K

TL;DR

This paper reports a novel electrochemical method to intercalate organic ions into FeSe crystals, significantly increasing the critical temperature to 43 K and enabling the synthesis of high-Tc organic-ion intercalated superconductors.

Contribution

It introduces an electrochemical synthesis technique for organic ion intercalation in FeSe, achieving high yields and enhanced superconducting properties.

Findings

Intercalation raises Tc from ~8 K to 43 K.

Layered crystal structure with disordered TMA+ ions.

Method allows high-yield synthesis of high-Tc materials.

Abstract

Intercalation of organic cations in superconducting iron selenide can significantly increase the critical temperature (Tc). We present an electrochemical method using beta-FeSe crystals (Tc ~ 8 K) floating on a mercury cathode to intercalate tetramethylammonium ions (TMA+) quantitatively to obtain bulk samples of (TMA)0.5Fe2Se2 with Tc = 43 K. The layered crystal structure is closely related to the ThCr2Si2-type with disordered TMA+ ions between the FeSe layers. Although the organic ions are not detectable by X-ray diffraction, packing requirements as well as first principle DFT calculations constrain the specified structure. Our synthetic route enables electrochemical intercalations of other organic cations with high yields to greatly optimize the superconducting properties, and to expand this class of high-Tc materials.