Effects of the voids filling on the lattice vibrations for the CoSb3-based thermoelectric materials—Raman scattering spectra and theoretical study

The unfilled CoSb3 and the voids filled skutterudites (La, Ce and La0.5Ce0.5) Fe3CoSb12 powders were synthesized via a hydrothermal route and the effects of the La and Ce filling in the voids on the Raman scattering spectra were investigated. The results suggest that the phonon vibration frequencies of the filled skutterudites in the lower frequency range shift down significantly, while the others in the higher frequency range shift up slightly as compared with the unfilled CoSb3. The calculated phonon frequencies for the (La, Ce and La0.5Ce0.5) Fe3CoSb12 indicate that all the frequencies shift down, but the frequency shifting down in the lower frequency range is more remarkable than that in the higher frequency range. By comparing the electron density differences of the unfilled CoSb3 and the voids filled (La, Ce and La0.5Ce0.5) Fe3CoSb12, the frequency shifting phenomena observed in the Raman scattering spectra may be attributed to the complex bonding behaviors between the La or Ce atoms with the parent Co and Sb atoms.