J. Mater. Chem. A, 9, 13883 (2021) [pdf] [SI]

Oxygen Ion Transport in Doped Ceria: Effect of Vacancy Trapping

Mehmet Emin Kilic, Jong-Ho Lee, Kwang-Ryeol Lee
 

Trivalent dopants in CeO₂ lattice generate the oxygen vacancies in the lattice, that is vital to oxygen diffusion. However, the dopant also has two detrimental effects on the oxygen vacancy migration: trapping the oxygen vacancies to the dopant and blocking the vacancy migration by increasing the energy barrier for the vacancy transport. We studied the diffusion of oxygen in Gd doped CeO₂ with La or Y co-dopants by using molecular dynamics (MD) simulation and compared them with the vacancy trapping and blocking behavior by the dopants. The trapping was characterized by the coordination number (CN) of cations statistically analyzed in large scale. The blocking caused by the dopants were investigated by the first principle nudged elastic band analysis. We found that the oxygen diffusion measured by the mean square displacement of oxygen in doped CeO₂ is enhanced when the trapping of oxygen vacancies is reduced by the co-doping. In contrast, the change in the energy barrier against oxygen migration in the co-doped lattice is not consistent with the diffusion behavior. This result evidently shows that the oxygen ion transport is governed by the trapping of oxygen vacancies.