High-order phonon anharmonicity in Yb-filled skutterudites

A study of the anharmonic phonon -scattering processes in Yb-filled CoSb3 skutterudite with low lattice thermal conductivity is carried out by combining temperature -dependent Raman -scattering measurements and first -principles calculations. The softening of the phonon frequency reveals the phonon anharmonicity. The two selected phonon modes exhibit strong cubic and quartic anharmonicity. The calculated weighted phase space and scattering rates of three- and four -phonon scattering further support the anharmonicity. At high temperatures, four -phonon scattering dominates the phonon -scattering processes at low frequencies. Fermi resonances among low -frequency phonons provide strong four -phonon scattering, leading to low lattice thermal conductivity. This study provides insight into the nature of anharmonic processes in highly efficient Yb-filled skutterudites and demonstrates the important role of the high -order phonon -phonon interactions in lowering lattice thermal conductivity.