Phonon localization and transport in disordered systems
1993; Elsevier BV; Volume: 164-166; Linguagem: Inglês
10.1016/0022-3093(93)91147-u
ISSN1873-4812
Autores Tópico(s)Phase-change materials and chalcogenides
ResumoWe suggest that the internal structure of glasses and amorphous materials is such that a mobility edge exists for lattice vibrations which we term ωc, below which energy the vibrational excitations are extended (phonons), and above which the vibrational excitations are localized. The energy width of the crossover region between these two extremes undoubtably connected with the temperature width of the plateau in the thermal conductivity, exhibited by nearly every glass or amorphous material. At the high temperature end of the plateau, the thermal conductivity κ(T) rises with increasing temperature. We attribute this increase to phonon assisted localized vibrational state hopping, associated with lattice anharmonicity. Comparing our calculated value for κ with experiment, the anharmonic coupling between extended and localized vibrational states is nearly an order of magnitude larger than for extended states alone. This value gives an excellent approximation to the temperature dependence of the velocity of sound arising from the same hopping mechanism. Recent theoretical modelling with a one dimensional Cantor set shows why this might be reasonable. Observations of anomalously long lifetimes for high energy lattice vibrations in a-Si and a-Si:H are consistent with this model.
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