Doping of ceria surfaces with lanthanum: aDFT + U study

Abstract

In this paper we use density functional theory corrected for on-site Coulomb interactions(DFT + U) to study the defects formed in the ceria (111) and (110) surfaces dopedwith La. To describe consistently the defect formed with substitutionalLa3 + doping at aCe4 + site we use DFTand DFT + U, withU = 5 eV for Ce 4f statesand U = 7 eV for O 2pstates. When La3 + substitutes on a Ce3 + site, an defect state, with an oxygen hole, is formed at both surfaces, but only with theDFT + U approach. The formation energy of an oxygen vacancy in a structure with two La dopantsin their most stable distribution is reduced over the undoped surfaces but remainspositive. Formation of an oxygen vacancy results in the appearance of a reducedCe3 + cation and a compensated oxygen hole, instead of compensation of both oxygen holes,which is typical of metal oxides doped with lower valence cations. We tentativelysuggest that the key role in the formation of this unusual defect is played bycerium and arises from the ease with which cerium can be reduced, as comparedto other metal oxides. Experimental confirmation of these results is suggested.