Molecular dynamics calculations on ceria-based solid electrolytes with different radius dopants

Oxygen diffusion and the microscopic structure of ceria-based solid electrolytes Ce_1-xM_xO_2-0.5x (M = La, Gd and Y) for x values between 0.02 and 0.3 were investigated by means of the molecular dynamics simulation. The compositional dependence of lattice parameters for the three dopants was in good agreement with experimental values. The calculated oxygen diffusion coefficient of Gd-doped ceria was larger than that of La- or Y-doped ceria as the experimental data showed. The nearest neighbor distance of Ce-O decreased and that of O-O increased with increase of the dopant content in the all doped cerias. The nearest neighbor distance of M-O increased in case of La doping, while it decreased in case of Y doping and the Gd-O distance was almost the same as the Ce-O distance in the non-doped ceria in case of Gd doping. The oxygen coordination number around a dopant was about seven for all cases, suggesting that dopant ions form a M-vacancy-M cluster. Large lattice distortion was observed in La- and Y-doped ceria, where the ionic radius of the dopant ion is fairly different from `optimum radius' of dopant in ceria. The reason why the oxygen diffusion coefficient is the largest in Gd-doped ceria is mainly explained in terms of the lattice distortion.