Model for the vibrational spectra of B2O3-xLi2O

A nested coherent-potential approximation in the Bethe lattice is used to model the vibrational spectra in the vitreous compound B2O3-xLi2O. A local-polarizability model is applied to calculate the Raman and infrared activity of the modes, and the results are compared with experimental data. The agreement is not complete due to the presence of rather complicated local configurations in the glass, as boroxol rings, diborate and tetraborate groups, not taken into account in the theory. However, this calculation is useful to identify the main features of the experimental spectra, and to corroborate the hypothesis of structural changes that occur when doping the pure boron oxide with an alkali-metal oxide.