Oxygen Vacancy Ordering and Electron Localization in CeO₂: Hybrid Functional Study

Abstract

Oxygen vacancies in bulk CeO 2 have been investigated using the Heyd−Scuseria−Ernzerhof (HSE) hybrid functional method. Results show that oxygen vacancies tend to linearly order in the ⟨111⟩ direction of CeO 2 , yielding much more dispersive gap states with the weakened electron localization compared to the case of a single vacancy. Such vacancy ordering and electron localization give rise to a profound influence on material properties. First, the dispersive gap states are expected to act as stepping stones to facilitate the electron excitation from valence band to conduction band, contributing to extended optical absorption in the longer wavelengths and thus enhancing photovoltaic and photocatalytic functionalities. Also, the linear ordering of oxygen vacancies leads to the electron localization on Ce ions and oxygen vacancy sites, inducing the polarization of electrons on vacancy sites which effectively enhances stability of ferromagnetism. The fundamental understanding of these functional mechanisms is presented in detail. Additionally, the kinetic analysis of the oxygen-vacancy cluster has also been performed, and its high kinetic stability suggests its physical existence in bulk CeO 2 . The outcome of this work offers great promise for practical application of CeO 2 in visible-light photocatalysis and photovoltaics as well as magneto-optic and spintronic devices.

Solubility of Nanocrystalline Cerium Dioxide: Experimental Data and Thermodynamic Modeling

“…Nano-ceria has already been widely used as a component of various catalysts, protective corrosion-resistant coatings for metals and alloys, polishing mixtures and abrasives 1-3, 12, 13 . It is anticipated that the production of engineered ceriabased nanomaterials will notably increase in the immediate future, because of emerging ceria applications in UV filters 4,5,14 , solid oxide fuel cells 6,7,[14][15][16][17][18] and pharmacology [8][9][10][11] . Rapidly growing demand in ceria-based materials inevitably results in their release to the environment (e.g.…”

Disentangling the role of small polarons and oxygen vacancies in CeO2

“…Recent studies focused on vacancy-vacancy interactions, but did not explore the single vacancy in CeO 2 [53].…”

Defect states and room temperature ferromagnetism in cerium oxide nanopowders prepared by decomposition of Ce-propionate

“…The higher ability of GBs to adsorb/trap the impurities (here vacancies) than the free surfaces was reported by others [47]. The ferromagnetism generated by defects such as oxygen vacancies at free surfaces of oxides is frequently reported [8,14,18]. However, the total solubility of impurity elements (e.g.…”

“…Nevertheless, there are studies which have demonstrated that a high concentration of oxygen vacancies and/or high density of states associated with these defects can induce RTFM in undoped CeO 2 [8,14,18]. Singhal et.…”

“…[2] associated ferromagnetism in bulk nondoped CeO 2 with a high density of oxygen vacancies induced by annealing in vacuum -the high density of F + centers reduces the F-electron orbital which is crucial to mediate the magnetic coupling. The hybrid functional method shows that kinetically stable oxygen-vacancy clusters, linearly ordered in the ⟨111⟩ direction [19], in the bulk CeO 2 could induce much more dispersive gap states with the weakened electron localization compared with the case of a single vacancy [18]; the electron localization at oxygen vacancy sites (and Ce ions), associated with this ordering, could enhance the ferromagnetism and its stability [18] in un-doped CeO 2 .…”