Microstructural Analysis of Sintered High‐Conductivity Zirconia with Al ₂ 0 ₃ Additions

Abstract

Transmission electron microscopy (at 100 and 1000 kV potential) and analytical scanning transmission electron microscopy were used to study α‐Al 2 0 3 second‐phase particles and their interactions with grain boundaries in two high‐conductivity Y 2 0 3 /Yb 2 0 3 stabilized zirconia ceramics containing deliberate additions of the alumina as a sintering aid. Most of the Al 2 0 3 particles were intragranular and microanalysis showed that they contained inclusions rich in Zr or Si plus Zr. Al 2 O 3 particles at grain boundaries were frequently associated with amorphous cusp areas rich in Si and Al. The results suggest that the Al 2 0 3 acts as a scavenger for SiO 2 , removing it from grain‐boundary localities. A model is proposed whereby this process occurs as the boundaries meet the second‐phase particles, assisted by rapid grain‐boundary diffusion. Such an ZrO 2 ‐Al 2 O 3 ‐SiO 2 interaction and partitioning is predicted thermodynamically and offers a possible explanation for the improvements in ionic conductivity brought about by Al 2 O 3 additions, as reported in the literature.