Ultralow thermal conductivity in two-dimensional MoO$_3$

TL;DR

This paper predicts that monolayer MoO$_3$ has an exceptionally low room-temperature phonon thermal conductivity due to its unique phonon interactions and bonding characteristics, making it promising for thermoelectric and thermal protection applications.

Contribution

It provides the first theoretical prediction of ultralow thermal conductivity in 2D MoO$_3$ using first-principles calculations and Boltzmann transport theory.

Findings

Record low $ppa_p$ of 1.57 W/mK along one in-plane direction.

Strong phonon scattering due to anharmonicity and mode coupling.

Insights for designing 2D materials with low thermal conductivity.

Abstract

Monolayer molybdenum trioxide (MoO$_3$) is an emerging two-dimensional (2D) material with high electrical conductivity. Using first-principles calculations and a Boltzmann transport theoretical framework, we predict record low room-temperature phonon thermal conductivity ($\kappa_p$) of 1.57 W/mK and 1.26 W/mK along the principal in-plane directions of MoO$_3$ monolayer. The behavior is attributed to the combination of soft flexural and in-plane acoustic modes, which are coupled through the finite layer thickness, and to the strong bonding anharmonicity, which gives rise to significant 3- and 4-phonon scattering events. These insights suggest new indicators for guiding the search of 2D materials with low $\kappa_p$. Our result motivates experimental $\kappa_p$ measurements in MoO$_3$, and its applications as a thermoelectric and thermally protective material.