Lattice dynamical investigations of Raman and infrared wavenumbers of scheelite structured silicates

Lattice dynamical investigations have been made for MSiO4 (M=Zr, Hf, U) silicates having space group I41/a and symmetry C64h by calculating Raman and infrared wavenumbers. Wilson's GF matrix method has been used with normal coordinate analysis to compute the zone center phonons. The model involves four stretching and six bending force constants for the calculation of wavenumbers. The calculated zone center frequencies show satisfactory agreement with the available experimental results. All the infrared wavenumbers have been computed for HfSiO4 and USiO4 in the present study. A complete assignment of modes for the calculated Raman and infrared frequencies has also been made. An appropriate assignment of infrared modes of HfSiO4 and USiO4 has been made by using theoretical calculations. Evaluation for potential energy distribution for each mode has been made to determine the role of force constants for Raman and infrared wavenumbers.