High‐Temperature Phase Relations in the System Y2O3‐Y2O3·WO3

Phase relations in the system Y₂O₃‐Y₂O₃·WO₃ were studied at >1400°C. Yttrium oxide with the rare‐earth C‐type structure transformed into a hexagonal structure at 2360° and melted at 2400°C. The eutectic between Y₂O₃ and 3Y₂O₃·WO₃ was 2334°C at ∼90 mol% Y₂O. 3Y₂O₃·WO₃ with a rhombohedral structure changed into a cubic phase at 1765° and melted at 2360°; 5Y₂O₃·2WO₃ with a tetragonal structure changed into the cubic phase at 1740°C. This cubic phase was stable at >1740° and had a solid‐solution range of 69 to 75 mol% Y₂O₃ at 1800°C. 7Y₂O₃·4WO₃ melted incongruently at 2107°C. Y₂O₃·WO₃ with a monoclinic structure (α’phase) transformed into an orthorhombic structure (e phase) at 1470°, then into a tetragonal structure (β phase) at 1600° to 1700°C. This compound melted incongruently at 1706°C. A phase diagram is given.