The electrical properties of 3mol%Y2O3-doped ZrO2 were measured by impedance spectroscopy, as a function of grain size, and the microstructure was studied by scanning electron microscopy and high-resolution transmission electron microscopy. In spite of the cleanliness of the grain boundaries, the grain boundary conductivity was still some 2 orders of magnitude lower than the bulk conductivity. It increased with decreasing grain size. A low grain boundary conductivity, according to the Schottky barrier model, was due to the depletion of O vacancies in the grain boundary space charge layers. Within this framework, the grain boundary space charge potential and the concentration of O vacancies in the space charge layers were calculated. It was found that the space charge potential decreased, but the O vacancy concentration increased, with decreasing grain size. An analysis of published results for 8.2mol%Y2O3- and 15mol%CaO-doped ZrO2 revealed similar phenomena.

Grain Size Dependent Grain Boundary Defect Structure - Case of Doped Zirconia. X.Guo, Z.Zhang: Acta Materialia, 2003, 51[9], 2539-47