Interaction of Cerium Oxide with Hafnium, Zirconium, and Yttrium Oxides at 1500°C

Using the methods of x-ray diffraction and petrographic analysis as well as electron microscopy, phase relationships in the ternary systems ZrO2 ― Y2O3 ― CeO2 and HfO2 ― Y2O3 ― CeO2 were investigated over the entire range of concentrations at 1500°C. The accuracy of the phase relationships of the binary systems HfO2 ― CeO2, ZrO2 ― CeO2, and CeO2 ― Y2O3 at this temperature was improved. Isothermal sections of the ternary phase diagrams at 1500°C were constructed. Specimens of various compositions were prepared from nitrate solutions by evaporating, drying, and heat treating at 1500°C. These systems are characterized by the formation of broad ranges of solid solutions based on C-Y2O3, F-CeO2, F-HfO2 and ZrO2, and narrow ranges based on T-ZrO2 and M-HfO2. No new phases were detected. The course of isoparametric lines in the solid solution ranges of F-HfO2 (ZrO2) leads to the assumption that yttrium and cerium ions substitute for each other, but no appreciable substitution by them for zirconium or hafnium ions occurs.