Chemistry

Scattering

Materials science

Physics

Ab initio

Quartic function

Acoustics

Quantum mechanics

Clathrate hydrate

Organic chemistry

Pure mathematics

Mathematics

Condensed matter physics

Thermodynamics

Anharmonicity

Hydrate

Lattice (music)

Thermal conductivity

Phonon

Physical Review Letters

We investigate the role of the quartic anharmonicity in lattice dynamics and thermal transport of type-I clathrate Ba$_{8}$Ga$_{16}$Ge$_{30}$ based on \textit{ab initio} self-consistent phonon calculations. We show that the strong quartic anharmonicity of rattling guest atoms causes the hardening of vibrational frequencies of low-lying optical modes and thereby affects calculated lattice thermal conductivities $\kappa_{L}$ significantly, resulting in an improved agreement with experimental results including the deviation from $\kappa_{L}\propto T^{-1}$ at high temperature. Moreover, our static simulations with various different cell volumes show a transition from crystal-like to \textit{glasslike} $\kappa_{L}$ around 20 K. Our analyses suggest that the resonance dip of $\kappa_{L}$ observed in clathrates with large guest-free-spaces is attributed mainly to the strong Umklapp scattering of acoustic modes along with the presence of higher-frequency dispersive optical modes.

Quartic Anharmonicity of Rattlers and Its Effect on Lattice Thermal Conductivity of Clathrates from First Principles