LATTICE-DYNAMICS AND NETWORK-DYNAMICS STUDIES OF VIBRATIONAL-MODES IN LITHIUM-DOPED BORATE GLASSES

The central-force nearest-neighbor model for glasses is used to discuss the Raman and infrared vibrational data for the family of lithium-doped borate glasses B2O3-xLi2O. The addition of the dopant is shown to cause local structural changes, including the transformation of threefold-coordinated borons to fourfold-coordinated ones. An extremely simple structural model for the glass gives good qualitative agreement with experiment. The results of lattice-dynamics calculations fall within the allowed frequency band limits predicted by network dynamics and give information on the distribution of modes within the bands. The success of this model illustrates the importance of short-range order on the vibrational spectra of covalently bonded solids. © 1990 The American Physical Society.