On the wave vector dependence of the Boson peak in silicate glasses and crystals

Recent work has demonstrated that a plausible explanation for the Boson pea k in silicate glasses is that it arises from transverse acoustic modes. We develop this argument further and put it on a firmer footing, by investigat ing the wave vector dependence of the Boson peak in inelastic neutron data. We make use of new results from an inelastic neutron scattering study of a crystalline polymorph of SiO2 (alpha-cristobalite). and of SiO2 glass and Li2Si2O5 glass. We find that the inelastic features in these three cases ma y be explained simply by arguments developed from phonon dispersion models of crystals. (C) 1999 Elsevier Science B.V. All rights reserved.