Search for: All records

Raman and infrared (IR) spectra provide rich information about materials. In this study, we employ first-principles calculations to predict the temperature-dependent linewidths of zone-center phonon modes, along with the IR dielectric function in bulk hexagonal boron nitride. We include the contributions of three-phonon, four-phonon scattering, and phonon renormalization, and our predictions show good agreement with our own experimental results as well as those in the literature. Our findings show that the temperature dependency of phonon linewidth would be strengthened by considering four-phonon scattering while weakened by further including phonon renormalization. After considering all these effects, four-phonon scattering shows a significant or even leading contribution to the linewidth over three-phonon scattering, especially at elevated temperatures. 

Despite its importance, a sophisticated theoretical study of thermal conductivity in bulk h-BN has been lacking to date. In this study, we predict thermal conductivity in bulk h-BN crystals using first-principles predictions and the Boltzmann transport equation. We consider three-phonon (3ph) scattering, four-phonon (4ph) scattering, and phonon renormalization. Our predicted thermal conductivity is 363 and 4.88 W/(m K) for the in-plane and out-of-plane directions at room temperature, respectively. Further analysis reveals that 4ph scattering reduces thermal conductivity, while phonon renormalization weakens phonon anharmonicity and increases thermal conductivity. Eventually, the in-plane and out-of-plane thermal conductivities show intriguing ∼T−0.627 and ∼T−0.568 dependencies, respectively, far deviating from the traditional 1/T relation. 

Abstract The prediction of thermal conductivity and radiative properties is crucial. However, computing phonon scattering, especially for four-phonon scattering, could be prohibitively expensive, and the thermal conductivity for silicon after considering four-phonon scattering is significantly under-predicted and not converged in the literature. Here we propose a method to estimate scattering rates from a small sample of scattering processes using maximum likelihood estimation. The calculation of scattering rates and associated thermal conductivity and radiative properties are dramatically accelerated by three to four orders of magnitude. This allows us to use an unprecedentedq-mesh (discretized grid in the reciprocal space) of 32 × 32 × 32 for calculating four-phonon scattering of silicon and achieve a converged thermal conductivity value that agrees much better with experiments. The accuracy and efficiency of our approach make it ideal for the high-throughput screening of materials for thermal and optical applications.