Influence of defect interactions on the free energy of reduction in pure and doped ceria

Ceria is known to release oxygen in reducing atmosphere leading to the formation of small polarons and oxygen vacancies. At high defect concentrations the interactions of defects play a growing role in the thermodynamics of defect formation especially in doped ceria, where mutual interactions between vacancies, dopant ions and localized electrons are present. Here, we simulated the distribution of defects in non-stoichiometric ceria with and without gadolinium doping by Monte Carlo methods based on an ab initio derived pair interaction model. From the simulations we extracted the change of the internal and free energy due to defect interactions. We investigated the influence of the free energy contribution on the reduction of ceria and modelled the relation between non-stoichiometry and oxygen partial pressure. The results are in agreement with experimental data, validating our simulation model and emphasizing the impact of defect interactions on the reduction of pure and doped ceria.