DEGREE OF STRUCTURAL DISORDER IN SODIUM METASILICATE GLASS - MODEL FOR RAMAN-SPECTRA

The mid- and high-frequency bands in the Raman spectrum of the alkali metasilicate glass Na2O . SiO2 above 500 cm(-1) are interpreted by mod elling the effects of Si-O-Si bridging angle, O-Si-O tetrahedral angle , dihedral angle and bond lengths disorder using Monte Carlo simulatio ns and second order perturbation theory for the averaged Green's funct ion. It is demonstrated that the Raman peaks are broadened by differen t structural mechanisms with FWHMs depending, in the first approximati on, linearly on the degree of structural disorder. A combined fit of t he experimentally observed FWHMs yields values for the relative degree of structural disorder corresponding to 16 degrees Si-O-Si disorder, 9 degrees O-Si-O disorder and 3.6% disorder in all the Si-O bond lengt hs, in good agreement with previous molecular dynamics results.