New Insight on the Effect of Yttria-Based Secondary Phases on Sintering and Electrical Behavior of Aluminum Nitride Ceramics

Full dense aluminum nitride ceramics (AlN) were prepared by hot-pressing sintering with and without yttrium oxide (Y2O3) as sintering aid. An intensive analysis of the AlN raw powder was performed to identify impurities. AlN grains appeared to be coated of an amorphous layer mainly composed of boehmite-like bonds. Thanks to the sintering process used all samples obtained exhibit high densification rate. The crystalized secondary phases identified by x-ray diffraction belong to the pseudo-binary Al2O3 – Y2O3. During sintering, AlN’s native oxide phase, observed on grains surface, plays a key role on formation of yttrium-based secondary phases such as YAM (Y4Al2O9), YAP (YAlO3) and YAG (Y3Al5O12). The formation of secondary phases was investigated thanks to quenching tests at different temperatures from 1400 to 1600 °C. Influence of secondary phases on DC electrical behavior was determined using current leakage measurement. The electrical properties appeared to be more impacted by the presence of these phases than by the densification improvement caused by yttria addition.