High temperature phase transition of Ce0.80Ln0.20O1.90−y and Ce0.70Ln0.30O1.85−y (Ln=Y, La, Gd) studied by heat capacity measurements

Heat capacities of Ce0.80Ln0.20O1.90 (Ln=Y, La, Gd), Ce0.80Y0.20O1.75, Ce0.80Gd0.20O1.77, Ce0.80La0.20O1.77, Ce0.70Y0.30O1.71, Ce0.70La0.30O1.74, Ce0.70Gd0.30O1.71 and Ce0.70Gd0.30O1.69 were measured by an adiabatic scanning calorimeter in the temperature range from 400 to 963 K. A heat capacity anomaly due to the phase transition from tetragonal to cubic structure was observed only in Ce0.80Gd0.20O1.77 at about 960 K, which was confirmed by X-ray diffraction. The other samples showed no heat capacity anomaly due to the presence of fluorite structure and the stability of the tetragonal structure related to the association of dopant cations and oxygen vacancies.