Charge Compensation and Ce 3+ Formation in Trivalent Doping of the CeO 2 (110) Surface: The Key Role of Dopant Ionic Radius

In this paper, we use density functional theory corrected for on-site Coulomb interactions (DFT + U ) and hybrid DFT (HSE06 functional) to study the defects formed when the ceria (110) surface is doped with a series of trivalent dopants, namely, Al 3+, Sc 3+, Y 3+, and In 3+ . Using the hybrid DFT HSE06 exchange-correlation functional as a benchmark, we show that doping the (110) surface with a single trivalent ion leads to formation of a localized M Ce / + O O • (M = the 3+ dopant), O − hole state, confirming the description found with DFT + U . We use DFT + U to investigate the energetics of dopant compensation through formation of the 2M Ce ′ +V O ·· defect, that is, compensation of two dopants with an oxygen vacancy. In conjunction with earlier work on La-doped CeO 2, we find that the stability of the compensating anion vacancy depends on the dopant ionic radius. For Al 3+, which has the smallest ionic radius, and Sc 3+ and In 3+, with intermediate ionic radii, formation of a compensating oxygen vacancy is stable. On the other hand, the Y 3+ dopant, with an ionic radius close to that of Ce 4+, shows a positive anion vacancy formation energy, as does La 3+, which is larger than Ce 4+ ( J. Phys.: Condens. Matter 2010, 20, 135004). When considering the resulting electronic structure, in Al 3+ doping, oxygen hole compensation is found. However, Sc 3+, In 3+, and Y 3+ show the formation of a reduced Ce 3+ cation and an uncompensated oxygen hole, similar to La 3+ . These results suggest that the ionic radius of trivalent dopants strongly influences the final defect formed when doping ceria with 3+ cations. In light of these findings, experimental investigations of these systems will be welcome.