Grain boundary blocking effect in zirconia: A Schottky barrier analysis

The grain boundary electrical properties of high purity ZrO(2), ceramic materials doped with 2, 3, and 8 mol % Y(2)O(3), and 8 mol % Y(2)O(3) co-doped with 0.4 mol % Al(2)O(3), were studied in the temperature range of 200 to 500 degreesC by electrochemical techniques and were theoretically analyzed. Although the presence of a siliceous phase is shown to be a major cause for the grain boundary blocking effect, the grain boundary properties appear to be significantly influenced by space charges, particularly in materials of high purity. The oxygen vacancy distribution and the grain boundary resistivity were calculated for 8 mol % Y(2)O(3) doped ZrO(2) by assuming double Schottky barriers, and the results were compared with the experiment. It is shown that reasonable space charge potentials lend to grain boundary effects which are consistent with the experimental features. In contrary to the bulk in which defect associates prevail (at temperatures <560C), in the boundary regions, association effects can be assumed to be much less pronounced due to the vacancy depletion. (C) 2001 The Electrochemical Society.