Phonon dispersion curves and densities of lithium-intercalated iron phosphorus trisulfide

Summary The lattice dynamics of Li-intercalated FePS₃ has been studied by means of a force constant model generated by a set of short-range two-body potentials. The intercalated phases have been investigated for the three stoichiometric compositions: Li_0.5FePS₃, LiFePS₃, Li_1.5FePS₃, with the aim of analysing the evolution of the host lattice normal modes as a function of the concentration, and of finding the dispersion of the new phonon branches induced by lithium. The above special values of lithium concentration have been chosen because the size of the unit cell keeps the same as in the host material. The force constants are fitted to the infrared data and the phonon dispersion curves and the phonon energy densities have been calculated. A spectroscopic method for monitoring lithium migration in the host material is proposed.