GRAIN-BOUNDARY IONIC-CONDUCTION IN ZIRCONIA-BASED SOLID-ELECTROLYTE WITH ALUMINA ADDITION

The grain boundary resistance of 9 mol% Y2O3-stabilized ZrO2 with Al2O 3 addition was measured by the complex impedance approach. The effect of Al2O3 addition on the grain boundary resistance was analyzed from t he aspects of microstructure and crystal defects by means of SEM, EPMA , TEM and the positron annihilation technique. The Al2O3 addition up t o 5 mol% was found to reduce the grain boundary resistance per unit su rface area of the grain boundaries and the activation energy for the g rain boundary resistance. This phenomenon was explained by the scaveng ing of the grain boundary impurities, e.g. SiO2, by the Al2O3 and the formation of the crystal grain boundary phases with very high defect c oncentration. By rite analyses with a simplified theoretical model, th e Al2O3 addition was considered to have no detrimental effect on the e mf of the ZrO2 oxygen sensor.