Dynamic process of the resonant phonon scattering in fully filled skutterudites

Abstract

The dynamics of the phonon scattering caused by the guest-host interactions in fully filled skutterudites $(\mathrm{Yb},\phantom{\rule{0.16em}{0ex}}\mathrm{La},\phantom{\rule{0.16em}{0ex}}\mathrm{Ba})\mathrm{F}{\mathrm{e}}_{4}\mathrm{S}{\mathrm{b}}_{12}$ are studied by ab initio molecular dynamics. The characteristics of filler vibrations are found to be the origin of ultralow lifetimes for the filler-dominant modes. Under the phonon-phonon interaction diagram, the large amplitudes of the filler vibrations and the coupling between filler and framework phonon modes greatly increase the strength of phonon scatterings. The lattice thermal conductivities for the three skutterudites, however, are all overestimated comparing with the experimental results. The introduction of the resonant scattering is thus necessary to account for the deviations. Furthermore, by applying the wavelet-based analysis to the resonant scattering process, the time-frequency power spectrum shows clearly that the time-varying localized motions of the fillers periodically absorb the heat-carrying lattice phonons and emit them. This process is the origin of the resonant scattering mechanism in skutterudites, and strongly interferes with the propagation of phonons near the frequency range of the fillers.