Raman scattering study of the skutterudite compounds

Raman scattering of skutterudite compounds RT 4 X 12 ( R = La , Ce, Pr, Nd, Sm and Yb, T = Fe , Ru and Os, X = P and Sb) have been measured. All first-order Raman active phonons are observed and are assigned as the pnictogen vibrations. At the low energy region, the second-order phonons, including the vibration of the rare-earth ions with a flat phonon dispersion, are observed in the spectra of SmRu 4 P 12 and ROs 4 Sb 12 . The second-order phonons can be observed for the sample with the larger cage space. The large displacement in the large cage space and the large density of state due to the flat phonon dispersion increase the intensity of the second-order Raman scattering process. The intensity of the second-order phonon are also affected by the valence of the rare-earth ions.