Vibrational spectra of rings in continuous silicon-oxygen networks

A method is proposed for modelling Raman and infrared spectra of crystalline and amorphous silicates on the basis of the vibrational modes of a ring of SiO4 tetrahedra with imposed boundary conditions. For the purpose a shell of first and second neighbours of the ring peripheral atoms is constructed and the structural disorder is introduced through averaging the dynamical matrix, dipole moment and polarisability tensor over all possible equilibrium configurations. It is shown that the Raman spectra of silicates in the frequency range 350-650 cm(-1) are suitable for studying the ring statistics in the material while the infrared absorption spectra in the range 550-850 cm(-1) are most appropriate to investigate the degree of intermediate range disorder.