Lattice dynamics of BaFe 2 X 3 ( X = S , Se ) compounds

We present the Raman scattering spectra of the BaFe2X3 (X = S, Se) compounds in a temperature range between 20 and 400 K. Although the crystal structures of these two compounds are both orthorhombic and very similar, they are not isostructural. The unit cell of BaFe2S3(BaFe2Se3) is base-centered Cmcm (primitive Pnma), giving 18 (36) modes to be observed in the Raman scattering experiment. We have detected almost all Raman active modes, predicted by factor group analysis, which can be observed from the cleavage planes of these compounds. Assignment of the observed Raman modes of BaFe2S(Se)(3) is supported by the lattice dynamics calculations. The antiferromagnetic long-range spin ordering in BaFe2Se3 below T-N = 255 K leaves a fingerprint both in the A(1g) and B-3g phonon mode linewidth and energy.