Inelastic neutron- and Raman-scattering studies of muscovite and vermiculite layered silicates

Investigations on the lattice dynamics of muscovite and vermiculite have been carried out by inelastic neutron scattering and Raman scattering. In the neutron measurements, dispersion curves for the out-of-plane and in-plane LA and TA phonons were fully obtained for muscovite, while more limited data were obtained for Mg vermiculite. Sound velocities were estimated from the slopes of the dispersion curves. Raman-scattering experiments revealed an interlayer shearing mode in Na and Sr vermiculites in the 0-water-layer hydration state. The intercalated water molecules in Na and Sr vermiculites exhibited a broad Raman feature (OH stretching vibrations) at 3450 ${\mathrm{cm}}^{\mathrm{-}1}$ with a full width at half maximum of ∼300 ${\mathrm{cm}}^{\mathrm{-}1}$. In addition, relatively sharp Raman peaks from the inner-layer hydroxyls in the host octahedral layers were found at ∼3700 ${\mathrm{cm}}^{\mathrm{-}1}$. These peaks were sensitive to the hydration state or charge in the intercalated layer.