Thermodynamic properties of transition-metal-doped cerium oxide with fluorite crystal structures

To identify factors that enhance thermochemical redox reaction efficiency, we have investigated the thermochemical properties of transition-metal-doped cerium oxide. This study examines thermodynamic parameters using vibrational entropy rather than configurational entropy and investigates how microscopic changes in bonding states affect macroscopic properties. VASP calculations show that vibrational entropy increases slightly upon doping with transition metals (Mn, Fe, Co, Ni); however, the magnitude of this change is limited. Specifically, for 3.125 mol% Mn-doped ceria, the reaction temperature at which Gibbs free energy (ΔG) becomes negative decreases and confirms a substantial improvement in redox reactivity. We further find that transition metal doping reduces the enthalpy required for oxygen vacancy formation, highlighting the dominant role of enthalpy over entropy in driving reaction feasibility when there are no significant changes in the crystal structure. Building on these findings, we present calculated results for ceria samples doped with 12.50 mol% and 25.00 mol% transition metals and compare them with the experimental data. These results provide a clear thermodynamic rationale for optimizing dopant species and concentration in solar redox materials.