Re-Investigation of Phase Equilibria and CALPHAD-Based Thermodynamic Optimization in the Gd2O3–La2O3–ZrO2 System

The isothermal phase equilibria of the Gd 2 O 3 –La 2 O 3 –ZrO 2 ternary system were experimentally determined at 1773 and 1573 K using a solid-phase reaction method. Continuous solid solutions of pyrochlore-type compounds (namely, Gd 2 Zr 2 O 7 and La 2 Zr 2 O 7 ) were confirmed across the ternary system, represented as La 2- x Gd x Zr 2 O 7 . The solubility limit of La 2 O 3 in the cubic fluorite ZrO 2 phase basically remains constant with decreasing temperature. The Gd 2 O 3 –La 2 O 3 –ZrO 2 ternary system was assessed by the CALculation of PHAse Diagrams (CALPHAD) method. The compound energy formalism (CEF) implemented was employed for thermodynamic descriptions of all phases within the CALPHAD method. A set of self-consistent thermodynamic parameters for the Gd 2 O 3 –La 2 O 3 –ZrO 2 system was derived.