Electrochemical intercalation of alkali metal – Lewis bases adducts into layered structure of iron chalcogenides

Abstract

The electrochemical intercalation of alkali metal – pyridine adducts into iron selenide matrix (FeSe0.98) was performed using galvanostatic conditions in two- and three-electrode setup. The system was examined using electrochemical impedance spectroscopy and analyzed with four-elements equivalent circuit, in which solution and charge transfer resistance, double layer capacitance, and Warburg impedance (diffusion) were identified. Charge transfer resistance was found to rise with increasing reaction time. X-ray powder diffraction analysis revealed elongation of the c axis as a result of intercalation and structural transition from primitive to body-centered unit cell in Na-intercalated system. Scanning electron microscopy with X-ray microanalysis, differential scanning calorimetry, and atomic emission spectroscopy confirmed introduction of guest species. Magnetic susceptibility measurements proved paramagnetic character of studied samples, with occurrence of transition to the superconducting state at around 9 ​K, similarly to the value observed in pure FeSe0.98.