Microstructural characterization and microstructural effects on the thermal conductivity of AlN(Y2O3) ceramics

Two different high density aluminum nitride (AlN) ceramic materials with Y2O3 as a sintering additive have been sintered at 1880°C, and characterized using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The lattice dissolved oxygen content, grain size and amount of secondary phase were fairly similar for the two materials, however, the thermal conductivity was quite different. SEM and TEM studies show that the secondary phase distribution along the grain boundaries or at grain junctions may have a major influence on the thermal conductivity. Microstructural changes were found to disrupt the connection between the high thermal conductivity AlN grains, resulting in a decrease in the thermal conductivity of the material as a whole. No amorphous layer was observed by high resolution transmission electron microscopy (HRTEM) at the cleanest grain boundaries in any of the materials.