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.