Experimental study of phase relations in the ZrO₂–La₂O₃–Y₂O₃ system

Abstract

Abstract Thermodynamic calculations in the ZrO 2 –La 2 O 3 –Y 2 O 3 system were used to select compositions for experimental investigations. The selected compositions were investigated using X-ray diffraction, scanning electron microscopy combined with energy dispersive X-ray spectroscopy and differential thermal analysis after prolonged heat treatment at 1250, 1400 and 1600 °C. The X-ray diffraction investigations indicated stability of the La 2 O 2 –A + (La,Y) 2 O 3 –B + La 2 Zr 2 O 7 and (La,Y) 2 O 3 –B + La 2 Zr 2 O 7 + LaYO 3 -perovskite phase fields at 1250 °C, which is contrary to results found in the literature. The differential thermal analysis of the ZrO 2 -45.8La 2 O 3 -20.8Y 2 O 3 composition heat treated at 1250 °C showed no transformations up to 1500 °C. Two peaks were indicated at temperatures above 1450 °C: the first peak at 1530 °C could be attributed to the processes of Y 2 O 3 dissolution and disordering in the pyrochlore phase and the second peak at 1580 °C to transformation of perovskite to monoclinic B phase. The solubility of Y 2 O 3 in pyrochlore phase occurs by Y +3 substitution of both Zr +4 and La +3 ions.