Thermal conductivity of high-temperature high-pressure synthesized θ -TaN

Recent first-principles calculation predicted that theta phase tantalum nitride (θ-TaN) single crystal has an ultrahigh thermal conductivity of ∼1000 W m−1 K−1 at room temperature, making it one of the best thermal conductors among all materials. Here, we have synthesized θ-TaN by phase change from ε-TaN powder at 1750 K and 7.8 GPa. X-ray diffraction patterns and scanning transmission electron microscopy indicate that the as-prepared θ-TaN has a hexagonal tungsten carbide structure with an average grain size of 45 nm. The room-temperature thermal conductivity of θ-TaN was measured to be 47.5 W m−1 K−1 using time-domain thermoreflectance. Temperature-dependent thermal conductivity suggests that phonon-boundary scattering dominates thermal transport. The thermal conductivity of our sample is higher than those of Si and SiC nanostructures with the same characteristic length. Our result suggests that it is probable to further increase the thermal conductivity of θ-TaN.