Low energy vibrational dynamics and connectivity in borate glasses

A study of the specific heat at low temperatures (1.5-25 K) of silver borate glasses has revealed the presence of an excess specific heat over the Debye contribution, which scales with the content. This observation has been related to the presence of non-bridging oxygens in the borate network, which are assumed to be a source for additional low-energy vibrations causing the excess . Furthermore, comparative measurements of and low-frequency Raman scattering (below ) at low temperatures in the same borate glass permit one to assess the frequency dependence of the photon-vibration coupling coefficient and the spectral density of low-energy vibrational modes . By comparison with the results obtained by the same procedure for vitreous , we show that a decreasing connectivity of the network leads to an increasing magnitude and softening of .