Origin of excess low-energy vibrations in densified B₂O₃ glasses

Abstract

Low-temperature experiments of Raman scattering and heat capacity have been performed in a B₂O₃ glass, pressure quenched from 1200 °C in order to obtain the density as largest as possible (ρ = 2373 kg/m³). When compared to those of compacted B₂O₃ glasses having smaller density, the Raman spectrum of this glass exhibits a strong decrease of the intensities of the Boson peak and the band at 808 cm⁻¹, both the features being determined by the decrease of the boroxol ring population. Moreover, the Boson peak exhibits a large shift to 68 cm⁻¹ (from 26 cm⁻¹ observed in normal vitreous B₂O₃). The high atomic packing of the glassy network also leads to a marked decrease of the excess heat capacity over the Debye T³-behaviour characterizing the crystal. The density g(ν) of low-frequency vibrational states has been assessed by using the low-frequency Raman intensity to determine the temperature dependence of the low-temperature heat capacity. The observations performed over a wide range of glass densities are compared to the predictions of theoretical models and computer simulations explaining the nature of the Boson peak. Consistency with the results of a simulation study concerning the vibrations of jammed particles leads to evaluate a nanometre length scale which suggests the existence of poorly packed domains formed from several connected boroxols. These soft regions are believed to be the main source of low-frequency optic-like vibrations giving rise to the Boson peak.

Keywords:

• glass
• vibrational properties
• specific heat

PACS number:

• 63.50.Lm
• 65.60.+a
• 78.30.Ly

Disclosure statement

No potential conflict of interest was reported by the authors.