ELECTRICAL-CONDUCTIVITY OF ALN CERAMICS AT HIGH-TEMPERATURES

The electrical conductivity of A/N ceramics with 4% Y2O3 and 1% CaO si ntering aids has been investigated with complex impedance spectroscopy at temperatures between 600-degrees-C and 1100-degrees-C. The impedan ce spectrum consists of a single arc with a relatively high capacitanc e. This behaviour can be interpreted using the brick layer model which leads to the conclusion that the A/N grains are covered with a contin uous layer of deviating composition. This is in agreement with SEM obs ervations. The results indicate that at high temperatures the resistiv ity of the sample is dominated by the grain boundaries present in the ceramic A/N sample. Using the brick layer model the average thickness of the grain boundary layers is estimated to be between 46 nm and 67 n m. The results also explain the independence of the electrical conduct ivity at high temperatures from the nitrogen partial pressure. The act ivation energy for electrical conductivity was found to be 2.4 eV. Fro m these results it is concluded that the electrical conduction is not related to the intrinsic properties of aluminium nitride.