Local symmetry breaking and spin-phonon coupling in SmCrO3 orthochromite

Raman scattering and infrared reflectivity performed on polycrystalline SmCrO3 support strong influence of the antiferromagnetic order on phonon modes. Both measurements show softening of some modes below TN. Such a behavior is explained by spin-phonon coupling in this compound. Furthermore, temperature dependence of the infrared spectra has demonstrated important changes compared to the Raman spectra, suggesting strong structural modifications due to the cation displacements rather to those of the oxygen ions. Our results reveal that polar distortions originating in local symmetry breaking, i.e. local non-centrosymmetry, resulting in Cr off-centring.