The influence of alumina addition and its distribution upon grain-boundary conduction in 15 mol.% calcia-stabilized zirconia

The improvement of grain-boundary conduction was studied in 15 mol.% calcia-stabilized zirconia (15CSZ) by adding Al₂O₃ in the forms of fine powder and single crystalline particles sized 4-10 μm as a scavenger for resistive siliceous phase. The addition of 1 mol.% Al₂O₃ improved the grain-boundary conduction when sintered at <1500°C, whereas it deteriorated at >1550°C. The restraining Al₂O₃ dissolution into inter-granular glass phase was a key feature for maximizing the scavenging efficiency. At 1450°C, the addition of single crystalline Al₂O₃ sized 4 and 10 μm enhanced grain-boundary conductivity by a factor of 14-16, whose enhancement was about twice of that by fine Al₂O₃ powder. It can be explained by the combination of the sufficient reaction path assisted by fast grain-boundary diffusion and the restraining glass phase formation by employing coarse and inactive single crystalline Al₂O₃ particles.