Influence of photoexcitation on the oxygen vacancy diffusion in Pr-doped CeO₂

CeO₂ and its compounds are employed in applications addressing various environmental- and energy-related issues such as solid oxide fuel cells and catalysis, among others. Oxygen storage capacity of CeO₂ is the ability to store and release oxygen and is a crucial property for efficient performance. It is coupled to the oxygen-vacancy formation and diffusion in the material. Praseodymium doping is used to promote oxygen-vacancy formation and migration to enhance ionic conductivity in this material. In this work, we study the Pr-doped CeO₂ with first-principles calculations and compute O vacancy diffusion barrier to assess the effects of photoexcitation on diffusion. Using the hybrid exchange-correlation functional, HSE06, we find that the two substitutional Pr ions prefer to occupy the next-nearest-neighbor (NNN) sites to the O vacancy over the nearest-neighbor (NN) sites in the supercell, in agreement with previous findings. We observe the emergence of four distinct in-gap defect states in the minority channel in comparison to the bulk CeO₂, with the charge density significantly localized around the Pr ions. To describe the O vacancy diffusion to the NN site, we determine the ground-state structure of the supercell by updating the vacancy site to the NN site, resulting in a total of six possible migration sites. Employing nudged-elastic band (NEB) approach we first compute the migration barrier of the O vacancy to the NN sites. To simulate photoexcitation, we promote an electron from the highest occupied to the lowest unoccupied band using constrained-density functional theory (CDFT) calculation. By combining CDFT and NEB we evaluate the migration barrier to the NN sites. Finally, we compute changes in the barrier without and with photoexcitation to assess the use of light to enhance vacancy migration and ionic conductivity in this technologically-relevant material.