Production of a grain boundary phase as conducting pathway in insulating AlN ceramics

We report that it is possible to render aluminum nitride (AlN) ceramics electrically conductive without losing their intrinsic high thermal conductivity by precipitating a yttrium oxycarbide grain boundary phase, the volume of which is about 1/20 that of the conducting phase in conventional ceramic composites. The electrical conductivity can be controlled by varying the sintering conditions and additive composition. In addition, the electrically conductive AlN can be shaped by electric discharge machining and converted back into insulating AlN by anodic oxidation.