Phase equilibria in the ZrO2-GdO1.5 system at 1400-1700 °C

Phase equilibria in the ZrO2-GdO1.5 system were studied experimentally in the whole composition range between 1400 and 1700 °C. Two different methods were introduced to obtain very fine powder, and dense samples were achieved by subsequent pressing and heat treatment. Equilibrated samples showed the presence of solid solutions based on zirconia and gadolinia polymorphs as well as of the intermediate pyrochlore-type phase. X-ray diffraction, scanning and transmission electron microscopy were employed to establish their homogeneity ranges. The contradictions in the literature regarding the extent of the pyrochlore-type solid solution field and phase equilibria in the GdO1.5-rich region were successfully resolved. The ordering of the fluorite phase was found to occur in the wide composition range, from 25 to 62 mol% GdO1.5, while the pyrochlore-type phase was detectable only between 44 and 54 mol% GdO1.5 (at 1400 °C).