Doping of ceria surfaces with lanthanum: a DFT +Ustudy

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 doped with La. To describe consistently the defect formed with substitutional La(3+) doping at a Ce(4+) site we use DFT and DFT + U, with U = 5 eV for Ce 4f states and U = 7 eV for O 2p states. When La(3+) substitutes on a Ce(3+) site, an La'(Ce) + O.(o)defect state, with an oxygen hole, is formed at both surfaces, but only with the DFT + U approach. The formation energy of an oxygen vacancy in a structure with two La dopants in their most stable distribution is reduced over the undoped surfaces but remains positive. Formation of an oxygen vacancy results in the appearance of a reduced Ce(3+) 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 tentatively suggest that the key role in the formation of this unusual defect is played by cerium and arises from the ease with which cerium can be reduced, as compared to other metal oxides. Experimental confirmation of these results is suggested.

On the interaction of Mg with the (111) and (110) surfaces of ceria

“…46,47 The application of DFT + U to ceria is well known and will not be discussed here. [10][11][12][13][14][15][16][17][20][21][22][39][40][41][42][43][44] In our work, the U parameter is 5 eV on Ce 4 f states. Hybrid DFT adds a portion of exact Hartree-Fock exchange to the local DFT energy, which helps to partially correct the self-interaction problem with local DFT.…”

Descriptor Analysis in Methanol Conversion on Doped CeO2(111): Guidelines for Selectivity Tuning

“…[40][41][42][43][44][45][46][47][48][49] Another trivalent dopant, Ga, enhances the activity of alkyne semi-hydrogenation, 50 69 This U eff was set to 4.5 eV, as it was been previously proven to provide satisfactory results. 55,[70][71][72] Projector-augmented wave (PAW) pseudopotentials 73 were used to describe the core electrons with a plane-wave cutoff energy of 500 eV for the valence electrons (i.e., 5s, 5p, 4f, 6s for Ce atoms, 2s, 2p for O and C atoms, 4s, 4p, 5s, 4d for Zr atoms, 5s, 5p, 6s, 5d for Hf atoms, and 6s, 6p, 5f, 7s for Th atoms).…”

The nature of oxygen states on the surfaces of CeO2 and La-doped CeO2

“…[24] Theoretical studies by Yeriskin and Nolan postulated that the defects were caused by O holes, which compensated the charge associated with the La dopants instead of the charge being compensated by removing an O anion. [25,26] The Kröger-Vink equation for this scheme is:…”