Density functional theory calculation on the effect of local structure of doped ceria on ionic conductivity

The oxide ionic conductivity of doped ceria was investigated from the viewpoint of local structure using first principles density functional theory (DFT) calculation. Singly doped ceria (DC) with Y, La, and Sm dopants (YDC, LDC, and SDC, respectively) and doubly doped ceria with equal amounts of Y and La dopants (CLY) were used as model lattices. The results obtained for doubly doped ceria (CLY) indicated that the energy difference variation with movement of oxide ion is mostly affected by the nearest neighbor cation arrangement of the moving oxide ion. For singly doped ceria, the order of the energy differences (ΔE) at the saddle points was estimated to be LDC>SDC>YDC, which is not completely consistent with the order of the activation energy obtained experimentally (LDC>YDC>SDC). The lowest ionic conductivity of LDC was reproduced by the DFT calculations, which was considered to be mainly brought about by the effect of the local cation arrangements of moving oxide ions. On the other hand, the order of ΔEʹs between YDC and SDC was reversed, which suggested that the effect of lattice deformation plays an important role in determining the ionic conductivity.