Phase Equilibria and Ordering in the System ZrO ₂ ‐Y ₂ O ₃

The phase diagram for the system ZrO 2 ‐Y 2 O 3 was redetermined. The extent of the fluorite‐type ZrO 2 ‐Y z O 3 solid solution field was determined with a high‐temperature X‐ray furnace, precise lattice parameter measurements, and a hydrothermal technique. Long range ordering occurred at 40 mol% Y 2 O 3 and the corresponding ordered phase was Zr 3 Y 4 OL 12 . The compound has rhombohedra1 symmetry (space group R 3), is isostructural with UY 6 O l2 and decomposes above 1250±50°C. The results indicate that the eutectoid may occur at a temperature <400°C at a composition between 20 and 30 mol% Y 2 O 3 Determination of the liquidus line indicated a eutectic at 83± 1 mol% Y 2 O 3 and a peritectic at 76 ± 1 mol% Y 2 O 3 .