Effects of firing schedule on solubility limits and transport properties of ZrO2-TiO2-Y2O3 fluorites |
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Authors: | DP Fagg JR Frade JTS Irvine |
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Institution: | a Aveiro University, Aveiro, Portugal b Risø National Laboratory, Roskilde, Denmark c St. Andrews University, St. Andrews, Fife, Scotland |
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Abstract: | The low Y/high Zr edge of the cubic defect fluorite solid solution in the system ZrO2-TiO2-Y2O3 in air is reassessed, as it is these compositions which have been suggested to offer the highest levels of mixed conductivity. Vegard's law is obeyed for values of x which lie within the cubic defect fluorite phase in Zr1−x−yYyTixO2−δ for values of y=0.2 and 0.25. Measured lattice parameters show good agreement with those calculated from the Kim relation. Deviation from Vegard's law places the limit of the solid solution at x=0.18 and 0.20 for values of y=0.2 and 0.25, respectively, at 1500 °C. Discrepancies in current literature data can be shown to be due to differences in firing schedule such as slight temperature fluctuations and/or different cooling rates. A high level of care of sintering temperature and cooling profile is essential to form the most promising single-phase materials which contain maximum Ti-contents with low Y-contents. Contraction of the phase limit as a result of poor synthesis control leads to erroneously high values of bulk ionic conductivity while values of electronic conductivity are shown to be less affected. |
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Keywords: | Fluorite Mixed conductor Phase limits Solid solubility Ionic conductivity |
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