We discuss how concepts from rigidity percolation can be used to understand the low frequency excitations and elastic properties of network glasses like GexAsySe1-x-t-y. When the mean coordination 〈r〉 = 2 + 2x + y is low, these materials are soft and their properties are strongly influenced by low frequency phonons. We use a bond depleted diamond lattice to mimic the coordination properties of the glass. We show that a model with only covalent forces is unstable for 〈rm〉 < 2.4, but can be stabilized by small additional forces. We calculate the elastic constants and the density of states as a function of 〈r〉. Despite the simplicity of the model, the rounded phase transition at 〈r> = 2.4 is consistent with recent experimental results involving ultrasonics and inelastic neutron scattering on Gexse1-x glasses. The floppy modes, observed in inelastic neutron scattering, disappear as 〈r〉 increases from 2 up to around 2.4.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Materials Chemistry