Oxygen vacancy diffusion and dynamics in Gd-doped CeO₂: A GGA+U study

Using a generalized gradient approximation + Hubbard U method in the framework of density functional theory, we investigate the oxygen vacancy (V_O) diffusion and dynamics in 3 × 3 × 3 CeO₂ supercells with two Gd substitutions for Ce and an oxygen vacancy. Results show that (i) V_O always migrates along the <100> direction, and (ii) V_O would rather migrate across the Ce–Ce edges than across Ce–Gd or Gd–Gd edges. Especially, Gd only positively influences the migrations of oxygen vacancies within the third nearest neighbor, indicating that the increased Gd doping is required for extending the positive influence to the long-distance diffusion of oxygen vacancy, which offers an accountable explanation for the enhanced ion conduction experimentally observed in CeO₂ with high Gd doping. The negative influence of heavy Gd doping on the V_O diffusion is also discussed in detail. The outcome of the current work has implications in illuminating the role of dopants toward expediting the oxygen vacancy diffusion and in promoting the performance in CeO₂-based materials and devices for environmentally friendly applications.