Thermodynamic investigation of the (La1−xGdx)2Zr2O7 pyrochlore phase

Abstract

Thermodynamic modeling of the ZrO2–Gd2O3–La2O3 system was achieved through the use of the CALPHAD (CALculation of PHAse Diagram) approach to investigate the phase stability of pyrochlore (La1−xGdx)2Zr2O7, a promising candidate material for thermal barrier coating (TBC) applications. The thermodynamic description of the pyrochlore phase in ZrO2–Gd2O3–La2O3 was extrapolated from the constituent pseudo-binaries and hypothetical end-members of the pyrochlore phase in La2O3–Gd2O3 were self-consistently derived from the reciprocal relationship. The isothermal sections at 1200 and 1500°C were calculated to elucidate the phase stability of pyrochlore, and the liquidus and solidus in the ternary system were calculated to determine temperature and characteristics of the ternary invariant reactions. Predicted phase stabilities show that pyrochlore dominates the phase stability in the temperature region considered, and its single-phase region shows potential for use in high-temperature thermal barrier coatings. The current thermodynamic study of ZrO2–Gd2O3–La2O3 can provide guideline to design pyrochlore phase for TBC applications, however, should be considered preliminary because of the lack of experimental information, particularly ternary phase equilibrium data, and awaits future experiments for further validation.