Anomalously strong size effect on thermal conductivity of diamond microparticles.

This article investigates the size-dependent thermal conductivity of synthetic diamond microparticles, revealing that their thermal conductivity increases significantly from about 400 to 2000 W m⁻¹ K⁻¹ as particle size grows from 20 to 300 μm. Contrary to prior assumptions that diamond microparticles exhibit thermal conductivity similar to bulk diamond due to phonon mean free paths, the study attributes this anomalous size effect to long-range defects formed during the high-pressure, high-temperature (HPHT) growth process rather than variations in point defects or dislocation density. Measurements using time-domain thermoreflectance (TDTR) indicate that these defects, possibly related to inhomogeneous strain and nanostructures, limit phonon transport in smaller particles. The findings have implications for optimizing synthetic diamond composites and thermal management materials by considering particle size and defect distribution.