Raman scattering of silicon clathrates

Silicon clathrates exhibit cagelike host lattices formed by 46 or 136 silicon atoms in which alkali atoms $M$ are trapped. The Raman spectra of the silicon clathrates ${\mathrm{K}}_8{\mathrm{Si}}_{46},$ ${\mathrm{Na}}_1{\mathrm{Si}}_{136},$ ${\mathrm{Na}}_6{\mathrm{Si}}_{136},$ and ${\mathrm{Na}}_{10}{\mathrm{Si}}_{136}$ are observed and compared with theoretical predictions determined from group theory and density of vibrational states simulations. These experimental results demonstrate the need of improved simulations of vibrational spectra.