Influence of Microstructure and Impurities on Thermal Conductivity of Aluminium Nitride Ceramics

The microstructure of AlN ceramics, which were pressureless sintered with CaO and CaF as additives, was modified via an annealing process. The thermal conductivity of these samples was measured and correlated with the microstructure changes. The influence of the microstructural elements, especially content and distribution of secondary phases, is described and quantitatively related to mixture models from literature for a full understanding of the relationships between microstructure, impurity content and thermal conductivity. The main result of the investigation is that the microstructural influence on thermal conductivity is limited to at maximum 41 W/m · K. The increase of the intrinsic thermal conductivity, due to loss of impurities especially oxygen during the beginning of the annealing process, is the main effect influencing thermal conductivity of sintered samples.