Electrical conductivity of AlN ceramics at high temperatures

Abstract

The electrical conductivity of AlN ceramics with 4% Y2O3 and 1% CaO sintering aids has been investigated with complex impedance spectroscopy at temperatures between 600°C and 1100°C. The impedance spectrum consists of a single arc with a relatively high capacitance. This behaviour can be interpreted using the brick layer model which leads to the conclusion that the AlN grains are covered with a continuous layer of deviating composition. This is in agreement with SEM observations. The results indicate that at high temperatures the resistivity of the sample is dominated by the grain boundaries present in the ceramic AlN sample. Using the brick layer model the average thickness of the grain boundary layers is estimated to be between 46 nm and 67 nm. The results also explain the independence of the electrical conductivity at high temperatures from the nitrogen partial pressure. The activation energy for electrical conductivity was found to be 2·4 eV. From these results it is concluded that the electrical conduction is not related to the intrinsic properties of aluminium nitride.