Polarized Raman-scattering study of Ge and Sn-filled CoSb3

Raman-scattering spectra of Ge-filled and Sn-filled CoSb3 were studied as a function of polarization. Polarized Raman-scattering spectra of CoSb3 were used to help distinguish the symmetry of each vibrational mode observed in the filled skutterudite specimens. Seven out of the eight Raman-active Sb vibrational modes of CoSb3 and the Ge-filled skutterudites were identified for each specimen. We also compare our experimental assignments with theoretical calculations for CoSb3. The Sn atoms rattle inside the voids of the crystal structure and interact strongly with the lattice vibrations to shift and broaden the Sb-vibrational modes as compared to the spectra of CoSb3. The smaller and lighter Ge atoms however do not have such an effect on the lattice vibrations, indicating that the interaction of Ge with the lattice is relatively weak in comparison. (C) 2003 American Institute of Physics.