Phonon Lifetimes and Thermal Conductivity of the Molecular Crystal $\hat{I}\pm$-RDX

Abstract

The heat transfer properties of the organic molecular crystal $\hat{I}\pm$-RDX were studied using three phonon-based thermal conductivity models. It was found that the widely used Peierls-Boltzmann model for thermal transport in crystalline materials breaks down for $\hat{I}\pm$-RDX. We show this breakdown is due to a large degree of anharmonicity that leads to a dominance of diffusive-like carriers. Despite being developed for disordered systems, the Allen-Feldman theory for thermal conductivity actually gives the best description of thermal transport. This is likely because diffusive carriers contribute to over 95% of the thermal conductivity in $\hat{I}\pm$-RDX. The dominance of diffusive carriers is larger than previously observed in other fully ordered crystalline systems. These results indicate than van-der Waals bonded organic crystalline solids conduct heat in a manner more akin to amorphous materials than simple atomic crystals.

Presented at 2019 MRS Spring Meeting & Exhibit, Phoenix Arizona, USA Session QN04.08.02, https://www.mrs.org/spring2019/symposium-sessions/symposium-sessions-detail?code=QN04 8 pages, 3 figures