Solid-state sintering of oxides involves a diffusion process of point defects. Some sintering models based on diffusion have been proposed. However, the application of these models needs a knowledge of the defect stru...
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Solid-state sintering of oxides involves a diffusion process of point defects. Some sintering models based on diffusion have been proposed. However, the application of these models needs a knowledge of the defect structure of oxides. The positron annihilation technique (PAT) is a suitable tool to study the solid-state sintering processes of oxides. The PAT study of the solid-state sintering of YS7 indicates that the cation interstitial diffusion plays an important role in the sintering.
According to a space-charge theory analysis, the space-charge potential of YSZ is negative, which corresponds to a V-0(..) depletion in the space-charge layer. An extremely low grain-boundary conductivity of the high-...
According to a space-charge theory analysis, the space-charge potential of YSZ is negative, which corresponds to a V-0(..) depletion in the space-charge layer. An extremely low grain-boundary conductivity of the high-purity YSZ is thus explained. Under the condition that the bulk property is ensured by the optimal dopant additions, an idea of increasing the grain-boundary conductivity by the segregations of solutes with positive effective charge is put forward. The most likely driving force for the segregations is the elastic strain energy. And the feasibility of this idea has been proved by some experimental and theoretical results.
A new destabilization phenomenon of fully-stabilized ZrO2 (FSZ) is studied by x-ray diffraction. The study has proved that H3BO3 can produce very severe destabilization in FSZ when heated at temperature higher than 80...
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A new destabilization phenomenon of fully-stabilized ZrO2 (FSZ) is studied by x-ray diffraction. The study has proved that H3BO3 can produce very severe destabilization in FSZ when heated at temperature higher than 800°C. The destabilization is summarized by two reactions.
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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