WO3 ADDITION, CRYSTAL PHASE EVOLUTION AND PROPERTIES OF Y2O3-DOPED AlN CERAMICS

The effect of WO3 addition as a substitute for Y2O3 on the densification, phase evolution, and properties of Y2O3-doped AlN ceramics sintered in a BN-coated graphite crucible at 1800 C for 3 h was studied. The total amount of oxides added was 4.5 wt%. In all of the compositions investigated, YAlO3 and Y4Al2O9 occurred as secondary phases. When WO3 was added, W2B was also identified. As the quantity of WO3 increased, the amount of YAlO3 and W2B increased and that of Y4Al2O9 decreased. However, the sinterability and thermal conductivity of the sintered body were not greatly affected. The optical reflectance decreased from 25 to approximately 10% in the visible-light regime, by the formation of W2B. For the sintered body with composition 3.5 Y2O3-1.0 WO3-95.5 AlN, the thermal conductivity, elastic modulus, and Poisson's ratio were 134 W/m.K, 368 GPa and 0.196, respectively, and the dielectric constant and loss tangent at a resonant frequency of 8.25 GHz were 8.60 and 0.003, respectively.