Intrinsic Lattice anharmonicity and thermal conductivity of PbTe at High Temperature: Breakdown of the Phonon Minimal Mean Free Path Theory

We investigated the vibrational property of lead telluride (PbTe) with a focus on lattice anharmonicity at relatively high temperatures using the phonon quasiparticle approach. The calculated anharmonic phonon dispersions are strongly temperature dependent and some phonon modes adopt giant frequency shifts. As a result, we witness the avoided crossing between transverse optical modes and longitudinal acoustic modes at elevated temperature, in good agreement with experimentation. These results reveal strong anharmonic effects in PbTe. The obtained phonon lifetimes allow studies of transport properties. For considered temperatures, the phonon mean free paths can be shorter than lattice constants at relatively high temperature, especially for optical modes. This finding goes against the widely employed minimal phonon mean free path concept. As such, the calculated lattice thermal conductivity of PbTe, which is indeed relatively small, does not have the prescribedminima at high temperature, showcasing the breakdown of the minimal mean free path theory. Our study provides a basis for delineating vibrational and transport properties of PbTe and other thermoelectric materials within the framework of the phonon gas model.