Experimental study of isothermal sections of the ZrO2–HfO2–Eu2O3 ternary diagram at 1500 °С and 1700 °С

In the present work the phase equilibria in a system of zirconium and hafnium dioxides and europium sesquioxide have been studied. The study was conducted at temperatures of 1700 °С and 1500 °С. Based on the results, isothermal sections at these temperatures were constructed. It was found that in the ZrО₂–HfO₂–Eu₂O₃ ternary system at temperatures of 1700 °С and 1500 °С solid solutions are formed on a monoclinic (M, space group P2₁/C) modification of HfO₂, a tetragonal (T, space group P4₂/nmc) modification of ZrO₂, cubic solid solutions ZrO₂ (HfO₂) with a fluorite structure (F, space group Fm3m), C-type cubic solid solutions of Eu₂O₃ (space group Ia-3), solid solutions based on the monoclinic modification (B, space group C2/m) of Eu₂O₃, as well as an ordered phase with a pyrochlore structure of Eu₂Zr₂O₇ (Eu₂Hf₂O₇) (Py, space group Fd-3m). The phase boundaries and the unit cell parameters of the formed phases were determined. The studied isothermal sections of the ZrО₂–HfO₂–Eu₂O₃ system are characterized by the formation of continuous series of cubic solid solutions based on the phase with a pyrochlore structure. The formation of new phases in the ZrО₂–HfO₂–Eu₂O₃ system at 1700 °С and 1500 °С was not observed.