A first-principles study on the phonon transport in layered BiCuOSe

TL;DR

This study uses first-principles calculations to analyze phonon transport in BiCuOSe, revealing its ultralow thermal conductivity due to strong anharmonicity and significant contributions from high-frequency optical phonons, with notable anisotropy.

Contribution

It provides the first detailed first-principles analysis of phonon transport in BiCuOSe, highlighting the role of high-frequency optical phonons and anisotropic thermal properties.

Findings

Ultralow lattice thermal conductivity due to strong anharmonicity.

High-frequency optical phonons contribute over one-third to thermal conductivity.

Anisotropic sound velocity and bulk modulus affect thermal transport.

Abstract

First-principles calculations are employed to investigate the phonon transport of BiCuOSe. Our calculations reproduce the lattice thermal conductivity of BiCuOSe. The calculated gruneisen parameter is 2.4~2.6 at room temperature, a fairly large value indicating a strong anharmonicity in BiCuOSe, which leads to its ultralow lattice thermal conductivity. The contribution to total thermal conductivity from high-frequency optical phonons, which are mostly contributed by the vibrations of O atoms, is larger than 1/3, remarkably different from the usual picture with very little contribution from high-frequency optical phonons. Our calculations show that both the high group velocities and low scattering processes involved make the high-frequency optical modes contribute considerably to the total lattice thermal conductivity. In addition, we show that the sound velocity and bulk modulus along $a$ and $c$ axes exhibit strong anisotropy, which results in the anisotropic thermal conductivity in BiCuOSe.