Raman scattering study of stoichiometric Si and Ge type II clathrates

Raman-scattering spectra of the type II clathrates Cs8Na16Si136, Cs8Na16Ge136, and Si-136 were studied employing different laser wavelengths. Most of the Raman-active vibrational modes of these compounds were identified. Polarization measurements were used to identify the symmetric modes. The lowest frequency Raman-active optic "rattle" mode corresponding to the vibrations of the Cs atoms inside the hexakaidecahedra is identified for both the Si and the Ge clathrate compounds. We compare the experimental data directly with theoretical calculations. These materials continue to attract attention for potential superconducting, optoelectronic, and thermoelectric applications. (C) 2002 American Institute of Physics.