Roles of rare earth oxide additives in millimeter-wave sintering of AlN

Abstract Roles of rare earth oxide (RE 2 O 3 ) additives in millimeter-wave(MM) sintering of AlN were investigated from the standpoints of phase diagram, heating characteristics of rare earth oxides, and morphology of intergranular oxide phase. In the millimeter-wave sintering of AlN, densification temperature decreased with the decrease of the ionic radius of rare earth ion and was closely related with the eutectic temperature in the RE 2 O 3 -Al 2 O 3 binary system. The lowest densification temperature in the millimeter-wave sintering of AlN with Yb 2 O 3 additive was attributed to the largest heating rate of Yb 2 O 3 ·Al 2 O 3 binary oxide under millimeter-wave radiation. Furthermore, the lowest densification temperature could be attained while selecting the Yb 2 O 3 content so as to form the intergranular phase with the eutectic composition in the Yb 2 O 3 -Al 2 O 3 binary system. The result showed good agreement with the above mentioned during the sintering of Si 3 N 4 with Yb 2 O 3 -Al 2 O 3 additive. From TEM observation, it was verified that film-like intergranular oxide phase formed under millimeter-wave radiation was favorable for attaining high thermal conductivity in the Yb 2 O 3 added AlNs.