Boson Peak, Elastic Properties, and Rigidification Induced by the Substitution of Nitrogen for Oxygen in Oxynitride Glasses
Résumé
The effects of the substitution of nitrogen for oxygen on the heat capacity and vibrational entropy of three yttrium aluminosilicate glasses with 0, 3.4, and 7.4 mol% Si(3)N(4) have been investigated from 10 to 300 K. The partial molar heat capacity and entropy of Si(3)N(4) calculated from these and previous measurements indicate stronger average bonding than for SiO(2) units, whereas the values derived for Y(2)O(3) are consistent with the dual network modifying and Al3+ charge-compensating role of yttrium. The low-frequency part of the vibrational densities of states g(omega) and the boson peaks g(omega)/omega 2 derived from the inversion of the heat capacities indicate that nitrogen rigidifies the TO(4) (T=Si, Al) tetrahedral network and that yttrium hampers the librational motion of the AlO(4) tetrahedra, which contribute to the excitations associated with the boson peak. Along with data reported previously for borate and silicate glasses, these results for oxynitrides show a general monotonically increasing relation between transverse acoustic velocities and the temperature of the calorimetric boson peak. Illustrating the universal phenomenology of the boson peak, all these data collapse on the same master curve when plotted in a reduced form.