Abstract
This work is directed towards a comprehensive study on the role of the microstructure and local chemistry of grain boundaries on the ionic conductivity of yttria (9 mol%)-stabilized zirconia and YSZ-alumina composites. It has been performed on samples prepared from two batches of YSZ powders containing ≈1.0 or 1.6 wt% SiO2. Electrical conductivity measurements show that the grain boundary conductivity (σgb) increases with the sintering temperature and the cooling rate at the end of sintering or when the amount of Si in the ceramic decreases. Alumina additions lead to a decrease in σgb of the samples containing 1.0 wt% SiO2, while σgb passes through a maximum in the highly silicon contaminated materials. These results coupled with TEM X-ray microanalysis, which have shown important gradients of the concentration ratio Al/Si in the grains, near the second phase, and in the glassy precipitates, suggest a competitive effect between the insulating alumina particles and the strong interaction of Al2O3 for SiO2, removing it from grain boundary localities. On the other hand, XPS analyses show that Si and Y segregate near the interfaces. Analysis of these results suggests a kinetic demixing process and allow us to explain the beneficial effect of a faster cooling rate at the end of sintering by the lower amount of Si rejected in grain-boundary localities.
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Rizea, A., Petot, C., Petot-Ervas, G. et al. Kinetic demixing and grain boundary conductivity of yttria-doped zirconia part I - experimental observations. Ionics 7, 72–80 (2001). https://doi.org/10.1007/BF02375469
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DOI: https://doi.org/10.1007/BF02375469