Phonon Dynamics in Amorphous Alloys

Normal vibration modes and vibrational density of states are fundamental for understanding many of the physical properties of materials, such as dynamical excitations, and mechanical and thermal transport properties. In crystalline materials, the normal modes, known as phonons, are quantized plane-wave solutions of the elemental modes of vibration. In amorphous materials, however, the phonon modes become far more complicated and are very different from those in crystals. Most notably, the phonon spectra become broadened, and the extent of broadening depends on the degree of disorder. Still, in amorphous materials, phonon-like dispersions have been predicted.  We use inelastic neutron scattering and computer simulation to study phonons in amorphous alloys.  Of particular interests are transverse phonons, which has been shown to persist well into the high-frequency regime in model glass systems.

Photonlike dispersion relationship in Zr46Cu46Al8 metallic glass. (a) and (c) are the phononlike density of states distribution obtained via inelastic neutron scattering experiment and molecular dynamic simulation respectively. (b) and (d) are the second derivatives of data in (a) and (c) respectively, which identified two phonon branches. The lower branch comes from the transverse phonons.

Key publication from our group:


[1]    X. Y. Li, H. P. Zhang, S. Lan, D. L. Abernathy, T. Otomo, F. W. Wang, Y. Ren, M. Z. Li, and X.-L. Wang, “Observation of High-Frequency Transverse Phonons in Metallic Glasses”, Physical Review Letters, 124, 225902 (2020).

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