Understanding Oxygen-Vacancy Migration in the Fluorite Oxide CeO<sub>2</sub>: An Ab Initio Study of Impurity-Anion Migration

Genreith-Schriever, A. R.; Hebbeker, Pascal; Hinterberg, Judith; Zacherle, Tobias; Souza, Roger A. De

doi:10.1021/acs.jpcc.5b07813

Cited by 29 publications

(26 citation statements)

References 56 publications

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“…The reason for this could be that the migration of single charged F − is less hindered than the migration of the double charged -O 2 . Genreith-Schriever et al [28] examined using computational methods the migration behaviour of various anions in CeO 2 and found that a higher negative charge on the migrating ion leads to a higher migration barrier. This would support our explanation for the observed difference between the F − and the -O 2 migration.…”

Section: Literature Discussionmentioning

confidence: 99%

“…One class of materials, for which both cases have been studied, is the family of AO 2 fluorite-structured oxides, such as ZrO 2 , HfO 2 , CeO 2 , ThO 2 , UO 2 and PuO 2 . Most of the published computational studies on these materials, however, only report activation barriers for oxygen-vacancy migration (from static calculations either based on densityfunctional-theory calculations [23][24][25][26][27][28][29] or based on empirical pair-potentials calculations [30][31][32][33][34][35]). The activation barrier for vacancy migration is predicted to be in the range of 0.4eV to 0.6 eV.…”

Section: Introductionmentioning

confidence: 99%

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Is excess faster than deficient? A molecular-dynamics study of oxygen-interstitial and oxygen-vacancy diffusion in CeO₂

Waldow

Souza

2020

J. Phys. Energy

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The diffusivity of oxygen interstitials (D i ) and of oxygen vacancies (D v ) in fluorite-structured CeO 2 was studied by means of classical molecular dynamic simulation techniques. Simulations were performed on cells that were either oxygen abundant or oxygen deficient at temperatures 1500 T / K 2000 for defect site fractions 0.18% n i/v 9.1%. In general, we found that at a given temperature T and defect site fraction n i/v the vacancy diffusivity D v was higher than the interstitial diffusivity D i . Isothermal values of D i and D v were constant at low defect site fractions (n i/v <0.91%), but the behaviour diverged at higher n i/v : whereas D v decreased at higher n v , D i increased at higher n i . The analysis also yielded, as a function of n i/v , activation enthalpies (ΔH mig ) and entropies (ΔS mig ) of vacancy migration and of interstitial migration. A constant value of D » H mig,v 0.6 eV was found for low n v , with increases in DH mig,v observed for n v > 0.91%. For low n i a constant value of D » H mig,i 1.4 eV was found, with a surprising decrease in DH mig,i for n i > 0.91%. The effect of dopants on the behaviour of the defect diffusivities was also studied. Doping with Gd 3+ had a detrimental effect on vacancy diffusion, with a slight decrease in D v and an increase in DH mig,v being observed. Donor doping with Nb 5+ , in contrast, was beneficial, resulting in higher D i and a decrease in DH mig,i . We suggest that the migration mechanism of oxygen interstitials in CeO 2 , non-collinear interstitialcy, is responsible for the lower defect diffusivity and higher migration barrier.

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Section: Literature Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Is excess faster than deficient? A molecular-dynamics study of oxygen-interstitial and oxygen-vacancy diffusion in CeO₂

Waldow

Souza

2020

J. Phys. Energy

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“…4) is similar, 48 and it is this environment that is expected to govern the energetics of the migration process. Indeed, according to Genreith-Schriever et al, 49 the repulsive Coulomb interactions between the migrating anion and the surrounding nextnearest-neighbour oxygen ions determine the energetics of anion migration in fluorite-based oxides.…”

Section: B Diffusionmentioning

confidence: 99%

Ion migration in crystalline and amorphous HfOX

Schie

Müller

Salinga

et al. 2017

The Journal of Chemical Physics

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The migration of ions in HfO x was investigated by means of large-scale, classical molecular-dynamics simulations over the temperature range 1000 ≤ T/K ≤ 2000. Amorphous HfO x was studied in both stoichiometric and oxygen-deficient forms (i.e., with x = 2 and x = 1.9875); oxygen-deficient cubic and monoclinic phases were also studied. The mean square displacement of oxygen ions was found to evolve linearly as a function of time for the crystalline phases, as expected, but displayed significant negative deviations from linear behavior for the amorphous phases, that is, the behavior was sub-diffusive. That oxygen-ion migration was observed for the stoichiometric amorphous phase argues strongly against applying the traditional model of vacancy-mediated migration in crystals to amorphous HfO 2 . In addition, cation migration, whilst not observed for the crystalline phases (as no cation defects were present), was observed for both amorphous phases. In order to obtain activation enthalpies of migration, the residence times of the migrating ions were analyzed. The analysis reveals four activation enthalpies for the two amorphous phases: 0.29 eV, 0.46 eV, and 0.66 eV (values very close to those obtained for the monoclinic structure) plus a higher enthalpy of at least 0.85 eV. In comparison, the cubic phase is characterized by a single value of 0.43 eV. Simple kinetic Monte Carlo simulations suggest that the sub-diffusive behavior arises from nanoscale confinement of the migrating ions. Published by AIP Publishing. [http://dx

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“…It is worth noting that, as revealed by the DFT calculations described later in this paper, the Y dopant atoms can also lower the formation energy of oxygen vacancies in doped ceria and therefore raise the saturation concentration of Ce 3+ . The migration energy for an oxygen ion to travel through the Y-Ce edge is close to that through the Ce-Ce edge (Nakayama & Martin, 2009;Genreith-Schriever et al, 2015). The similar ionic radii of Y 3+ and Ce 4+ also warrants that the Y doping only incurs limited structural deformation.…”

Section: Resultsmentioning

confidence: 93%

Defect engineering by synchrotron radiation X-rays in CeO₂ nanocrystals

Syu

Weng

et al. 2018

J Synchrotron Radiat

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This work reports an unconventional defect engineering approach using synchrotron-radiation-based X-rays on ceria nanocrystal catalysts of particle sizes 4.4-10.6 nm. The generation of a large number of oxygen-vacancy defects (OVDs), and therefore an effective reduction of cations, has been found in CeO catalytic materials bombarded by high-intensity synchrotron X-ray beams of beam size 1.5 mm × 0.5 mm, photon energies of 5.5-7.8 keV and photon fluxes up to 1.53 × 10 photons s. The experimentally observed cation reduction was theoretically explained by a first-principles formation-energy calculation for oxygen vacancy defects. The results clearly indicate that OVD formation is mainly a result of X-ray-excited core holes that give rise to valence holes through electron down conversion in the material. Thermal annealing and subvalent Y-doping were also employed to modulate the efficiency of oxygen escape, providing extra control on the X-ray-induced OVD generating process. Both the core-hole-dominated bond breaking and oxygen escape mechanisms play pivotal roles for efficient OVD formation. This X-ray irradiation approach, as an alternative defect engineering method, can be applied to a wide variety of nanostructured materials for physical-property modification.

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Understanding Oxygen-Vacancy Migration in the Fluorite Oxide CeO₂: An Ab Initio Study of Impurity-Anion Migration

Cited by 29 publications

References 56 publications

Is excess faster than deficient? A molecular-dynamics study of oxygen-interstitial and oxygen-vacancy diffusion in CeO₂

Is excess faster than deficient? A molecular-dynamics study of oxygen-interstitial and oxygen-vacancy diffusion in CeO₂

Ion migration in crystalline and amorphous HfOX

Defect engineering by synchrotron radiation X-rays in CeO₂ nanocrystals

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Understanding Oxygen-Vacancy Migration in the Fluorite Oxide CeO2: An Ab Initio Study of Impurity-Anion Migration

Cited by 29 publications

References 56 publications

Is excess faster than deficient? A molecular-dynamics study of oxygen-interstitial and oxygen-vacancy diffusion in CeO2

Is excess faster than deficient? A molecular-dynamics study of oxygen-interstitial and oxygen-vacancy diffusion in CeO2

Ion migration in crystalline and amorphous HfOX

Defect engineering by synchrotron radiation X-rays in CeO2 nanocrystals

Contact Info

Product

Resources

About

Understanding Oxygen-Vacancy Migration in the Fluorite Oxide CeO₂: An Ab Initio Study of Impurity-Anion Migration

Is excess faster than deficient? A molecular-dynamics study of oxygen-interstitial and oxygen-vacancy diffusion in CeO₂

Is excess faster than deficient? A molecular-dynamics study of oxygen-interstitial and oxygen-vacancy diffusion in CeO₂

Defect engineering by synchrotron radiation X-rays in CeO₂ nanocrystals