Effect of alumina addition on the microstructure and grain boundary resistance of magnesia partially-stabilized zirconia

Abstract The electrical properties of 9 mol% MgO–ZrO 2 (Mg-PSZ) with 1 mol% Al 2 O 3 and the mechanisms for electrical degradation were investigated using structural, morphological, and electrochemical analyses. The addition of Al 2 O 3 caused an increase in both the monoclinic and the Mg-rich phases at the grain boundaries in the Mg-PSZ. Coarse grains larger than 20 μm and an intergranular layer composed of the Mg-rich phase were identified in a specimen sintered at 1600 °C. This specimen exhibited a minimum of ionic conductivity (4.98 × 10 −4  S cm −1 at 700 °C) due to the grain boundary resistance (245 Ω cm 2 ), which dominated the overall resistance. A similar trend was observed over the entire temperature range (600–1500 °C). An intergranular siliceous impurity (SiO 2 ) was present in conjunction with the Mg-rich phase. This impurity and the Mg-rich phase acted as a barrier layer for oxygen ion diffusion. The presence of the intergranular phases (i.e. the monoclinic and Mg-rich phases) contributed to the degradation of the ionic conductivity in Mg-PSZ with an Al 2 O 3 addition.

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