According to a space-charge theory analysis, the space-charge potential of YSZ is negative, which corresponds to an Y-Zr' segregation and an V-O(..) depletion in the space-charge layers. Owing to the highly disord...
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According to a space-charge theory analysis, the space-charge potential of YSZ is negative, which corresponds to an Y-Zr' segregation and an V-O(..) depletion in the space-charge layers. Owing to the highly disordered structure of the grain-boundary interfaces, the resistance of the interfaces is considered to be negligible with respect to that of the space-charge layers, the intrinsic grain-boundary resistivity in stabilized-ZrO2 was thus considered to originate from the V-O(..) depletion in the space-charge layers, and an intrinsic grain-boundary resistivity model was developed. With this model, all the grain-boundary resistivity behaviors in stabilized-ZrO2 with high-purity described in the published litteratures were satisfactorily explained.
Up to 5 mol% Al2O3 was added to 9 mol% Y2O3-stabilized ZrO2, and the roles of Al2O3 were systematically studied by means of the complex impedance approach, the positron annihilation technique, SEM, TEM, and electron p...
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Up to 5 mol% Al2O3 was added to 9 mol% Y2O3-stabilized ZrO2, and the roles of Al2O3 were systematically studied by means of the complex impedance approach, the positron annihilation technique, SEM, TEM, and electron probe microanalysis from the following aspects: (1) the existence of forms of Al2O3 in ZrO2, (2) the effects of Al2O3 on the microstructure of ZrO2, (3) the effects of Al2O3 on the resistance of ZrO2, (4) the microstructure and property changes of ZrO2 with Al2O3 addition during ageing at 940 degrees C. Two types of grain boundary phase, crystal and amorphous, were discovered. The Al2O3 segregation at grain boundaries can promote the mobility of the grain boundaries and thus results in a low density, because of entrapped pores. The Al2O3 addition decreases the grain-boundary resistance in two ways: to scavenge the SiO2 and CaO located at grain boundaries, and to form crystal grain-boundary phases with very high crystal defect concentrations. Ordered microdomains of Zr3Y4O12 were precipitated from ZrO2 grains during ageing, and aluminium was found to facilitate the precipitation.
On the basis of experiments, the ZrO2 grain boundaries are classified into three types: the ''clean'' grain boundaries, the grain boundaries with amorphous phases and the grain boundaries with crystal ...
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On the basis of experiments, the ZrO2 grain boundaries are classified into three types: the ''clean'' grain boundaries, the grain boundaries with amorphous phases and the grain boundaries with crystal phases. The structure and property of the three types of grain boundaries were analyzed from the aspects of microstructure and lattice defects, and the conductivity of the crystal grain boundary phases was calculated with the effective-medium theory to be as three times higher as that of the matrix, an idea of further enhancing the ionic conduction of ZrO2 by modifying grain boundaries was thus proposed. The effect of the ZrO2 grain boundaries on the EMF of the oxygen sensor was discussed with simplified models.
A feasible way to further enhance the ionic conduction of ZrO2 is to decrease the grain boundary resistivity by adding new ingredients. Thus, the effect of the addition of Al2O3, the only oxide that has been found to ...
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A feasible way to further enhance the ionic conduction of ZrO2 is to decrease the grain boundary resistivity by adding new ingredients. Thus, the effect of the addition of Al2O3, the only oxide that has been found to reduce ZrO2 resistivity, on the ionic conductivity of ZrO2 was investigated, and the results are reported in this paper.
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