Grain boundary phase in AlN ceramics fired under reducing N2 atmosphere with carbon

An AlN ceramic was prepared with a dopant Y2O3 under a reducing nitrogen atmosphere with carbon at 1900 °C for 20 h. The AlN ceramic had thermal conductivity, 220 W/m°C, which contained crystalline Y2O3 and an amorphous intergranular film. The intergranular phase decreased during the isothermal hold period by the migration of a liquid phase that consisted of Y2O3, Al2O3, and AlN. The liquid phase composition was maintained during the firing process. Comparison of the microstructures of the ceramics prepared with different isothermal hold times revealed that the lower the quantity of intergranular phase, the higher the thermal conductivity attained.