Effect of Li2O on sintering of AlN ceramics at low temperature

XRD, SEM and TEM were employed to study the mechanism of low temperature sintering of AlN ceramics with Li2O, CaF2 and Y2O3 as additives. The results show that the AlN ceramics containing Li2O have a lower temperature at which AlN begins to shrink and a larger shrinkage at 1650°C due to the promotion of the glass phase containing Li and liquid CaYAlO4. Li2O not only changes the phase compositions but also improves the properties of the liquid phase in the AlN ceramics during the sintering. The glass phase containing Li is formed from the reaction between Li2O and Al2O3 below 1100°C, which significantly decreases the starting temperature of AlN shrinkage. Above 1600°C, the glass phase containing Li is lost because of the decomposition and evaporation of Li2O, which purifies the grain boundaries of AlN. The transformation from CaYAl3O7 to CaYAlO4, which exists in AlN in liquid form, simultaneously makes the continuous shrinkage possible after Li2O is evaporated.