Sub-solidus phase equilibria in the CeO2–ThO2–ZrO2 system

The phase relations in the CeO2–ThO2–ZrO2 system have been established after slowly cooling the samples from 1400 °C. Ceria has been used as a surrogate material in place of plutonia. The various phase boundaries were delineated by refining the powder XRD data. Thoria and ceria were shown to form an ideal solid solution in the complete homogeneity range. About 5 and 20 mol.% of zirconia can be dissolved, under the heating conditions used in the present investigations, in the lattice of thoria and ceria, respectively. In the ZrO2–Th0.5Ce0.5O2 system, 10 mol.% zirconia was found to get incorporated in the lattice of Th0.5Ce0.5O2. The (Th0.5Zr0.5)1−xCexO2 system shows the formation of single-phase solid solutions from x⩾0.70. Thorium rich compositions in (Ce0.5Zr0.5)1−xThxO2 system were also found to be cubic solid solution. In addition, a number of other phases like t-ZrO2, various two-phase and multi-phase regions could also be identified in this pseudo-ternary system.