Lamb-Mössbauer factors as a local probe of floppy modes in network glasses

• Published in: Journal of non-crystalline solids 1995-03, Vol.182 (1), p.143-154
• Main Authors: Boolchand, P., Bresser, W., Zhang, M., Wu, Y., Wells, J., Enzweiler, R.N.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Lattice dynamics; Physics; Vibrational states in disordered systems
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/0022-3093(94)00540-0

The temperature dependence of the Lamb-Mössbauer factor, f( T), in a solid provides the first inverse, 〈 1 ω 〉 , and second inverse, 〈 1 ω 2 〉 , moments of the vibrational density of states. In network glasses, these moments serve as local probes of low-frequency vibrational excitations, such as floppy modes, and provide a means to establish the rigidity percolation threshold. Lamb-Mössbauer results on prototypical chalcogenide glasses (Ge x Se 1− x ) correlate well with those of Raman scattering, inelastic neutron scattering and Mössbauer hyperfine structure experiments in indicating that the rigidity percolation threshold occurs near 〈 r〉 c = 2.46(4). These observations provide experimental support for predictions of the Phillips-Thorpe constraint theory, when provision is made for a small but finite concentration of broken bond-bending constraints around chalcogen sites.