Phase equilibria in the ZrO2-YO1.5-TaO2.5 system at 1500 °C

The ZrO2-YO1.5-TaO2.5 (ZYTO) system is of interest in phosphors, fuel cells, photocatalysis, and thermal barrier coatings. However, there is inadequate information on the ternary phase equilibria, especially in the ZrO2-lean compositions. Precursor derived ZYTO compacts were heat treated at 1500 degrees C to elucidate the relevant phase relations. Chemical compositions measured using TEM/EDS and crystallographic information via x-ray diffraction, Raman spectroscopy and selected area electron diffraction were used to construct the isothermal section at 1500 degrees C, which was found to vary significantly from previous reports. It is shown for the first time that the fluorite field extends from the YO1.5-ZrO2 binary to the YO1.5-TaO2.5 binary, revealing a large YTaO4 + fluorite phase field with potential engineering implications. The mutual solubility of ZrO2 and YTaO4 was quantified, and the presence of both YTa3O9 and YTa7O19 at 1500 degrees C was demonstrated. The emerging understanding helps identify compositions with potentially attractive properties for further investigation. (C) 2017 Elsevier Ltd. All rights reserved.