Boson peak of alkali and alkaline earth silicate glasses: influence of the nature and size of the network-modifying cation.

The influence of the size of the alkaline earth cation on the boson peak of binary metasilicate glasses, MSiO(3) (M = Mg, Ca, Sr, Ba), has been investigated from vibrational densities of states determined by inversion of low-temperature heat capacities. As given both by C(p)/T(3) and g(ω)/ω(2), the intensity of the boson peak undergoes a 7-fold increase from Mg to Ba, whereas its temperature and frequency correlatively decrease from 18 to 10 K and from 100 to 20 cm(-1), respectively. The boson peak results from a combination of librations of SiO(4) tetrahedra and localized vibrations of network-modifying cations with non-bridging oxygens whose contribution increases markedly with the ionic radius of the alkaline earth.

The boson peak of silicate glasses: the role of Si-O, Al-O, and Si-N bonds.

The role of Si-O, Al-O, and Si-N bonds on the boson peak of silicate glasses has been investigated from a study of amorphous Si, SiO(2), and two calcium aluminosilicates with 0 (Ca28-O) and 4.4 (Ca28-N) mol % Si(3)N(4). The low-frequency part of the vibrational density of states g(omega) has been calculated from inversion of literature data and new heat capacity measurements.