Fe Chalcogenides by X-ray Photoemission Spectroscopy

In this article, x-ray photoelectron spectroscopy (XPS) spectra of iron chalcogenides, FeS, Fe₇S₈, and Fe₇Se₈ are presented. FeS (troilite) and Fe₇S₈ (pyrrhotite) are among the most common iron compounds on earth. FeS is antiferromagnetic below the Néel temperature of T_N=593-598 K. Above T_α=420 K, FeS is a metal with an NiAs-type crystal structure, but becomes an insulator with a narrow band gap of 0.04 eV below T_α. This transition known as the α-transition is accompanied by a small displacement of the Fe and S atoms from the regular NiAs-type structure. Fe₇S₈ and Fe₇Se₈ are ferrimagnetic metals with Néel temperatures of T_N=578 and 423-460 K, respectively. The crystal structures of Fe₇S₈ and Fe₇Se₈ are derived from the NiAs-type one by introducing ordered Fe vacancies. The polycrystalline samples were synthesized by the Bridgman method. Clean surfaces were obtained by scraping in situ with a diamond file. All the XPS spectra of the iron chalcogenides are taken at room temperature.