Effect of Silica on the Thermal Conductivity of Aluminum Nitride

Abstract

The effect of SiO2 on the thermal conductivity of aluminum nitride pressureless sintered with 3 wt% Y2O3 as a sintering aid was investigated. SiO2 additions greatly decreased the thermal conductivity of the sintered parts from values of around 160 W/m·K on undoped samples to about 25 W/m·K with 5 wt% SiO2 added to the green body composition. Microstructural studies, combined with the temperature dependence of the thermal conductivity and lattice parameter measurements, indicated that defect phonon scattering was the mechanism responsible for the decrease in thermal conductivity. SiO2 can be incorporated in limited solid solution into the AIN lattice, generating AI vacancies for charge compensation in a process not unlike the solution of oxygen in AIN. The mass difference introduced by the vacancies is the main phonon scattering defect. Beyond a concentration threshold of 2%, the SiO2‐induced defects cluster to form SiAION polytypoids derived from the basic 2H AIN structure with stacking sequences that depend on the SiO2 levels in the sample.