Effects of Li2O on the low temperature sintering and thermal conductivity of AlN ceramics

Effects of Li2O on the densification and the thermal conductivity of AlN ceramics sintered at a low temperature were studied by using Li2CO3, CaF2 and Y2O3 as additives. DTA and XRD were employed to identify the formation of the liquid and the changes of the phase compositions during the sintering. SEM and TEM were used to observe the microstructures of AlN specimens sintered at 1650 °C. The results show that Li2O is an effective sintering aid, leading to high densification and high thermal conductivity at low sintering temperatures. AlN specimens with full densification and thermal conductivity were achieved with Li2O addition. The high densification comes from the promotion of the liquid containing Li and CaYAlO4. The high thermal conductivity is attributed to the purification of the AlN lattice, the enhancement of the density and the elimination of some grain-boundary phases.