Raman Active Phonons in RCoO₃ (R=La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy) Perovskites

We examine RCoO₃ (R=La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy) perovskites prepared with the solid-state reaction method by Raman spectroscopy, and report the Raman active phonons in the RCoO₃ perovskites crystallized in cubic symmetry for RCoO₃ (R=La, Ce, Pr and Nd) and orthorhombic symmetry for RCoO₃ (R=Sm, Eu, Gd, and Dy). It is found that the Raman spectra of RCoO₃ perovskites are strongly dependent on the ionic radius of the rare earth elements, and the frequency shift of the most intense modes of the orthorhombic samples are correlated with some structural parameters such as Co--O bond distances, ionic radius of the rare earth elements and Jahn--Teller distortion. It is clear that Raman spectroscopy has the advantage of sensitivity to structure distortion and oxygen motion.