Experimental investigation and thermodynamic modelling in the ZrO2–La2O3–Y2O3 system

Abstract

Abstract Phase equilibria in the La 2 Zr 2 O 7 –Y 2 O 3 join were studied in the temperature interval between 1250 and 1600 °C using the X-ray diffraction and thermal analysis. It was demonstrated that the maximal solubility of Y 2 O 3 in the La 2 Zr 2 O 7 (pyrochlore structure) was approximately 20 mol% of Y 2 O 3 . In mixtures containing more than 20 mol% Y 2 O 3 the La 2 Zr 2 O 7 reacted with Y 2 O 3 forming the fluorite structure at increasing temperature. The compound energy formalism was applied to describe solubility of Y 2 O 3 in pyrochlore structure assuming that Y 3+ can occupy both La 3+ and Zr 4+ enriched sites in the crystal structure. The Gibbs energies of compounds with pyrochlore structure were assessed. Ternary mixing parameters were included in thermodynamic description of the fluorite phase to reproduce in calculations its wide homogeneity range extending from ZrO 2 –Y 2 O 3 binary in the direction of LaYO 3 . Calculated phase diagrams reproduce general character of experimental data.