Effects of Y2O3 additions on the densification and thermal conductivity of spark plasma sintering AlN ceramics

Spark plasma sintering (SPS) of AlN ceramics was carried out with Y2O3 as a sintering additive at sintering temperatures of 1,550 to 1,700 degrees C. The effects of Y2O3 additions on the sintering behavior and thermal conductivity of AlN ceramics were studied. Y2O3 added to AlN showed a noticeable higher densification rate than pure AlN, but the formation of yttrium aluminate phases by the solid-state reaction of Y2O3 and Al2O3 occurred on the AlN surface which could retard the densification during the sintering process. The thermal conductivity of AlN specimens was improved by the addition Of Y2O3 up to 3 wt% in spite of the formation of a YAG secondary phase in the AlN grAlN boundaries because Y2O3 additions could reduce the oxygen content in the AlN lattice which is primary factor controlling the thermal conductivity. However, the thermal conductivity decreased at a 5 wt% addition because the extra formation of the YAG phase in grAlN boundaries could decrease the thermal conductivity by phonon scattering thus surpassing the helpful contributions of smaller Y2O3 additions.