The effects of three types of additives Y 2 O 3 , La 2 O 3 , and Sm 2 O 3 on the sintering and mechanical behaviors of alumina ceramics were investigated. The bending strengths of alumina ceramics with Sm 2 O 3 and Y 2 O 3 additions were 455 and 439 MPa, respectively, higher than that with La 2 O 3 addition. The fracture toughness of the ceramics with Sm 2 O 3 and Y 2 O 3 were also higher than that with La 2 O 3 addition. The fracture mode of rare earth oxides doped alumina ceramics exhibited obvious transgranular fractures as well as intergranular fracture. The results of research show that the improvement of bending strength and fracture toughness of alumina ceramics with rare earth oxides was achieved by refining the grain size and strengthening the grain boundary.

The effects of Y 2 O 3 and Er 2 O 3 on the sintering behaviors, thermal properties and microstructure of AlN ceramics were investigated. The experimental results show that the sintering temperature can be decreased; the relative density and thermal behavior can be improved by adding rare earth oxide in AlN ceramics. For AlN ceramics with 3 wt.% Er 2 O 3 additive, the relative density is 98.8%, and the thermal conductivity reaches 106 W·m −1 ·K −1 . The microstructure research found that no obvious aluminum erbium oxide was found in AlN ceramics doped with 3 wt.% Er 2 O 3 , which favored the improvement of the thermal conductivity of AlN ceramics.