Raman Scattering Study of Cubic–Tetragonal Phase Transition in Zr_1−xCe_xO₂ Solid Solution

A structural phase transition between the cubic (space group, Fm3m) and tetragonal (space group, P4₂/nmc) phases in a zirconia–ceria solid solution (Zr_1−xCe_xO₂) has been observed by Raman spectroscopy. The cubic–tetragonal (c–t″) phase boundary in compositionally homogeneous samples exists at a composition X₀ (0.8 < X₀ < 0.9) at room temperature, where t″ is defined as a tetragonal phase whose axial ratio c/a equals unity. The axial ratio c/a decreases with an increase of ceria concentration and becomes 1 at a composition X′₀ (0.65 < X′₀ < 0.7) at room temperature. The sample with a composition between X₀ and X′₀ is t″ ZrO₂. By Raman scattering measurements at high temperatures, the tetragonal (t″) → cubic and cubic → tetragonal phase transitions occur above 400°C in Zr_0.2 Ce_0.8O₂ solid solution.