LATTICE-DYNAMICS OF LAYERED MPX3 (M=MN,FE,NI,ZN, X=S,SE) COMPOUNDS

An experimental and theoretical study of the lattice dynamics of MPX3 layered compounds (M =Mn, Fe,Ni, Zn; X =S,Se) has been carried out. We present room-temperature infrared and Raman spectra and the phonon dispersion curves calculated in the framework of an axially symmetric force-constant model. The parameters of the dynamical model have been fitted on the Raman and ir data, consistently with the conditions of static equilibrium and of vanishing stress. A satisfactory assignment of the vibrational bands and a qualitative explanation of the dynamical differences among the materials are obtained. Moreover, the theoretical results support the hypothesis of phonon branches folding effects in the antiferromagnetic phase of FePS3 and provide the basis for an interpretive scheme of the vibrational spectra of lithium intercalated phases.