Grain boundary blocking effects in Sm/Yb-doped AlN ceramics

Abstract

The effect of microstructural changes on the electrical and thermal properties of AlN ceramics is studied in terms of cation size and nature of sintering aids (i.e. Sm2O3 and Yb2O3) in AlN ceramics. It is revealed that the addition of Yb2O3 to Sm-bearing AlN ceramics results in 80 % reduction of thermal conductivity with an increase of the grain boundary resistivity that is one order of magnitude larger than for the sample without Yb2O3. Additionally, the grain boundary/grain resistivity ratio is significantly increased, when the Sm2O3 sintering aid is employed instead of Yb2O3, for which the secondary phases at the grain boundaries and the triple junctions are responsible for the increase in the electrical resistivity. The microstructural investigations confirm the tendency of the secondary phase to segregate at the triple junctions in Sm-containing AlN ceramics while it is grain boundaries that are favored as segregation site in the case of Yb.