THE VIBRATIONAL-MODES OF VITREOUS B2O3

The vibrational density of states of vitreous B2O3 has been studied over its full energy range by the use of two different inelastic neutron scattering spectrometers. Its general features may be described in terms of four bands of modes centred at 6.8, 15.1, 88 and 171 meV. A simple model for the vibrational density of states based on a single triangular BO3 structural unit shows the character of the modes for each of the four bands. There is evidence in the vibrational density of states for low energy modes in excess of the sound wave contribution. The above model suggests that the excess may be due to rotational modes, although this explanation might be invalidated by frustration due to the high concentration of boroxol rings.