The role of materials’ interfaces/grain boundaries on enhancing anion conductivity is a hotly debated issue that has exposed limited understanding on point-defect energetics at interfaces. Using density functional theory (DFT) and interatomic simulations on zirconia, ceria and other related materials, we unravel key interface issues, i.e., oxygen vacancy migration barriers at interfaces in the absence and presence of dopants, and oxygen vacancy-dopant binding energies at interfaces. We show that pure, strained interfaces indeed possess very low oxygen migration barriers; however, the segregated dopants counteract and raise the barriers significantly.
In addition, the dopants bind oxygen vacancies much more strongly at the interfaces than in the bulk, thereby further lowering oxygen diffusivity at interfaces. From DFT calculations, we also show that that strained interfaces could lead to formation of metastable phases that can ultimately dictate unintuitive oxygen vacancy stability. We conclude that the concept of strained interfaces to enhance anion conductivity prevails primarily in the absence of segregated dopants, and strategies that prevent dopant segregation need to be considered in the design of anion-conducting interfacial and nanocrystalline materials.