Structures of Defect Clusters on Ceria {111} Surface

Defect clusters containing oxygen vacancies and Ce3+ cations on ceria (CeO2) surface dominate the electronic and chemical properties of the surface. However, the structures of the clusters, especially the arrangements of the oxygen vacancies in the clusters, have not been explained consistently. In this work, atomistic simulation based on energy minimization has been used to investigate the cluster structures on ceria {111} surface. It was found out that the oxygen vacancies are energetically favorable to be at the second-neighbor sites to their associated Ce3+ cations. Moreover, the subsurface oxygen vacancies on the third layer are essential for the arrangement of the surface oxygen vacancy clusters. Due to the existence of the subsurface oxygen vacancies, the adjacent surface oxygen vacancies tend to be separated by ⟨110⟩/2, and the linear surface clusters are more energetically favorable than the triangle ones. Then, the structure development with cluster size is discussed.