Modeling the tunable thermal conductivity of intercalated layered materials with three-directional anisotropic phonon dispersion and relaxation times

An analytical model using three-directional anisotropic (TDA) dispersion and a novel anisotropic relaxation time (RT) relation for modeling the thermal conductivity (k) of intercalated layered materials is developed. The TDA dispersion eliminates the restriction of in-plane isotropy and is suitable for TDA materials such as black phosphorous. We compare calculations of k of bulk intercalated layered materials using the isotropic Debye dispersion and BvK dispersion with our TDA dispersion model, paired with both isotropic and anisotropic RTs. We find that calculated k values by the TDA dispersion model agree best with the experimental data. Furthermore, anisotropic RTs largely improve the performance of the Debye and BvK dispersion models whose average relative deviations for the in-plane k are reduced from 17.3% and 23.0% to 4.4% and 8.5%, respectively. Finally, thermal conductivity accumulation functions of intercalated MoS₂ and graphite are numerically calculated based on the TDA dispersion with anisotropic RTs. These models predict that intercalants cause increased contributions from phonons with shorter mean free paths, especially for in-plane thermal conductivity.