Phase Equilibria in the ZrO2–CeO2–Yb2O3 System at 1100°C

Abstract

Phase equilibria and structural transformations in the ternary ZrO2–CeO2–Yb2O3 system at 1100°C were studied by X-ray diffraction over the entire composition range. Fields of solid solutions based on monoclinic (M) and tetragonal (T) ZrO2 modifications, cubic (C) Yb2O3 modification, cubic fluorite-type (F) CeO2 (ZrO2) modification, and an intermediate Zr3Yb4O12 (δ) orthorhombic phase were found to exist in the system. The boundaries of the phase fields and lattice parameters of the phases were determined. The maximum solubility of cerium oxide in the δ phase was 4 mol.% at the CeO2–(60 mol.% ZrO2–40 mol.% Yb2O3) section. Solid solutions based on the tetragonal ZrO2 modification were established to form in the region with high ZrO2 content. The solubility of Yb2O3 in T-ZrO2 is low and comes to δ0.5 mol.%, which is evidenced by X-ray diffraction and microstructural analyses. The solid solutions based on the tetragonal ZrO2 modification cannot be quenched from high temperatures in the chosen cooling conditions. An infinite series of F-CeO2(ZrO2) solid solutions forms at 1100°C. The isothermal section of the ZrO2–CeO2–Yb2O3 system at 1100°C contains one three-phase region (F + C + δ), five single-phase regions (FCeO2(ZrO2), M-ZrO2, T-ZrO2, δ, C-Yb2O3), and five two-phase regions (C + F, C + δ, F + δ, F + T, T + M). New phases were not found in the system. The nature of phase equilibria in the ternary ZrO2–CeO2–Yb2O3 system at 1100°C is determined by the constitution of binary phase diagrams.