A Model to Understand the Oxygen Vacancy Formation in Zr-Doped CeO₂: Electrostatic Interaction and Structural Relaxation

Using density functional theory with the inclusion of on-site Coulomb correction, the O vacancy formation energies of CexZr1−xO2 solid solutions with a series of Ce/Zr ratios are calculated, and a model to understand the results is proposed. It consists of electrostatic and structural relaxation terms, and the latter is found to play a vital role in affecting the O vacancy formation energies. Using this model, several long-standing questions in the field, such as why ceria with 50% ZrO2 usually exhibit the best oxygen storage capacity, can be explained. Some implications of the new interpretation are also discussed.