Unusual Mössbauer phenomenon inLixFePS3

Abstract

Lithium intercalation in layered (two-dimensional) ${\mathrm{FePS}}_3$ was studied by ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectroscopy, which shows the presence of two iron sites Fe(A) and Fe(B) for the ${\mathrm{Li}}_{\mathrm{x}}$ ${\mathrm{FePS}}_3$ (x≠0) system. The Mössbauer characteristics of the Fe(A) site remain almost identical to those of the iron site in the host ${\mathrm{FePS}}_3$. The Mössbauer peaks of the Fe(B) site, which corresponds to the reduced iron, increase with lithium intercalation. The smaller isomer shift found for the Fe(B) site is peculiar in the light of all known previous Mössbauer data, and has been attributed to a greater overlap distortion of core orbitals and/or to a greater 4s electron population on the Fe(B) site than on the Fe(A) site. According to the relative intensity of the Fe(B) site as a function of lithium intercalation, the Fe(B) site is apparently consistent with a zero-oxidation-state iron atom.