VIBRATIONAL SPECTROSCOPY OF THE AMORPHOUS SILICATES

It has been demonstrated that the Si2O unit instead of the SiO4 unit a pproach would much better explain the IR spectra of crystalline and vi treous silica and framework alumino-silicates. In this approach all mo des are lattice vibrations other than Si2O unit vibrations. Within the lattice vibrations it is suggested to distinguish: high-wavenumber ps eudo-lattice vibrations in the 700-400 cm-1 range and low-wavenumber l attice vibrations below 300 cm-1. The first range is responsible for s ome kind of order larger than a single unit, while the second one cove rs the long range order in the structure. Similarities between the spe ctra of crystalline and vitreous forms of respective silicates indicat e a structural relationship between the medium range structural order of glass and the relevant crystal structure. The detailed discussion a nd conclusions are based on the far-infrared, mid-infrared and Raman s pectra measured for vitreous and crystalline potassium silicates and p otassium alumino-silicates. The spectra of silica polymorphs measured at different temperatures are also presented and discussed.