Thermal conductivity of AlN ceramic with a very low amount of grain boundary phase at 4 to 1000 K

An AlN ceramic fired at 2173 K for 100 h under a reduced N₂ atmosphere with carbon possessed a room-temperature conductivity of 272 Wm⁻¹K⁻¹, slightly lower than the value for high-purity, single-crystal AlN. However, the thermal conductivity of the ceramic at temperatures below 100 K was much lower than that of single crystal. This is mainly due to phonon scattering by grain junctions that possess an amorphous film with a thickness of under 1 nm. At 500 to 1000 K, no significant difference in the conductivity was observed between the ceramic and the single crystal.