Microscopic mechanism of low thermal conductivity in lead-telluride

TL;DR

This paper investigates the microscopic origins of low thermal conductivity in lead telluride, revealing how phonon interactions and anharmonic effects reduce heat transport, with implications for thermoelectric materials.

Contribution

It provides a first-principles analysis of phonon scattering mechanisms and their role in low thermal conductivity of PbTe, highlighting the significance of optical phonons.

Findings

Longitudinal acoustic phonons are scattered by transverse optical phonons with high anharmonicity.

Soft transverse acoustic phonons have small group velocities, reducing heat conduction.

Optical phonons contribute more to heat transport than typically expected in bulk materials.

Abstract

The microscopic physics behind low lattice thermal conductivity of single crystal rocksalt lead telluride (PbTe) is investigated. Mode-dependent phonon (normal and umklapp) scattering rates and their impact on thermal conductivity were quantified by the first-principles-based anharmonic lattice dynamics calculations that accurately reproduce thermal conductivity in a wide temperature range. The low thermal conductivity of PbTe is attributed to the scattering of longitudinal acoustic phonons by transverse optical phonons with large anharmonicity, and small group velocity of the soft transverse acoustic phonons. This results in enhancing the relative contribution of optical phonons, which are usually minor heat carrier in bulk materials.