Nanoscale spatially resolved thermal transport in nanocrystalline 3C-SiC

This study investigates spatially resolved phonon-mediated thermal transport across nano-sized grains and grain boundaries (GBs) in 3C-SiC using molecular dynamics (MD) simulations. This investigation involves controlling the complete range of inter-grain misorientation tilt angles (θ = 0°–90°) and nanoscale grain sizes (d = 2.18–130.77 nm). The grain boundary energy and interfacial thermal transport are found to be highly θ-sensitive and asymmetric with respect to θ = 45° due to the low symmetry associated with two interpenetrating diatomic SiC fcc lattices. When adjacent grains are tilted at θ = 14.25°, the interfacial heat conduction is highly suppressed compared to other θ values, especially for larger grains. The most stable atomic configuration of the GB region associated with the minimal GB energy results in the highest suppression of heat conduction across the GB interface. Spatially resolved thermal anisotropy reveals a strong GB-mediated nanoscale hydrodynamic phonon Poiseuille effect when heat flows parallel to the GB planes, as shown by our perturbed MD study. With the reduction of d, the intra-grain and inter-GB thermal conductivities decrease due to the enhanced phonon scattering from interfaces, but the difference between these conductivities becomes negligible for the heat flow normal to the GB planes. It is envisioned that nanoscale spatially resolved control of thermal energy will provide useful guidance to engineer nanocrystalline ceramics with tunable interfacial thermal properties.