A combined DFT + U and Monte Carlo study on rare earth doped ceria

Grieshammer, Steffen; Grope, Benjamin O. H.; Koettgen, Julius; Martin, Manfred

doi:10.1039/c3cp54811b

Cited by 117 publications

(188 citation statements)

References 84 publications

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“…This is probably due to the significantly smaller radius of Sc, which leads to Sc clustering that overrides the effect of the elastic strain field. Extensive clustering of Sc cations in bulk ceria is known 44 . The geometry and location of enrichment and depletion zones may change for other types of dislocations in ceria, depending on their strain-stress field.…”

Section: Resultsmentioning

confidence: 99%

Edge dislocation slows down oxide ion diffusion in doped CeO2 by segregation of charged defects

2015

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Strained oxide thin films are of interest for accelerating oxide ion conduction in electrochemical devices. Although the effect of elastic strain has been uncovered theoretically, the effect of dislocations on the diffusion kinetics in such strained oxides is yet unclear. Here we investigate a 1/2o1104{100} edge dislocation by performing atomistic simulations in 4-12% doped CeO 2 as a model fast ion conductor. At equilibrium, depending on the size of the dopant, trivalent cations and oxygen vacancies are found to simultaneously enrich or deplete either in the compressive or in the tensile strain fields around the dislocation. The associative interactions among the point defects in the enrichment zone and the lack of oxygen vacancies in the depletion zone slow down oxide ion transport. This finding is contrary to the fast diffusion of atoms along the dislocations in metals and should be considered when assessing the effects of strain on oxide ion conductivity.

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Section: Resultsmentioning

confidence: 99%

Edge dislocation slows down oxide ion diffusion in doped CeO2 by segregation of charged defects

2015

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“…(Under very reducing conditions, singly‐charged oxygen vacancies, and even neutral oxygen vacancies, have to be taken into account, but in our study we remain in the oxidizing regime and so both these species can be safely neglected.) For the dilute regime (

c_{a}

< 1%), we also neglect defect–defect interactions . We note that the electrons are localized on Ce 4+ ions as small polarons, forming Ce 3+ ions.…”

Section: Continuum Simulationsmentioning

confidence: 99%

“…This is due to such compositions displaying the highest oxide‐ion conductivities, and the driving force behind the research has been optimizing the ionic conductivity of CeO 2 ‐based ceramics, so that they can be used as electrolytes in solid oxide fuel cells (SOFC). Such solid solutions, however, constitute materials systems in which defect–defect interactions are evidently important . The analysis of the SCLs at the GBs of such concentrated solid solutions, on the other hand, has been based on the dilute‐solution approximation (Poisson–Boltzmann ansatz), in which defect–defect interactions are neglected.…”

Section: Introductionmentioning

confidence: 99%

The grain‐boundary resistance of CeO₂ ceramics: A combined microscopy‐spectroscopy‐simulation study of a dilute solution

Parras

Chun-xiao

et al. 2019

J Am Ceram Soc

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Weakly acceptor‐doped ceria ceramics were characterized structurally and compositionally with advanced transmission electron microscopy (TEM) techniques and electrically with electrochemical impedance spectroscopy (EIS). The grain boundaries studied with TEM were found to be free of second phases. The impedance spectra, acquired in the range 703 ≤ T/K ≤ 893 in air, showed several arcs that were analyzed in terms of bulk, grain‐boundary, and electrode responses. We ascribed the grain‐boundary resistance to the presence of space‐charge layers. Continuum‐level simulations were used to calculate charge‐carrier distributions (of acceptor cations, oxygen vacancies, and electrons) in these space‐charge layers. The acceptor cations were assumed to be mobile at high (sintering) temperatures but immobile at the temperatures of the EIS measurements. Space‐charge formation was assumed to be driven by the segregation of oxygen vacancies to the grain‐boundary core. Comparisons of data from the simulations and from the EIS measurements yielded space‐charge potentials and the segregation energy of vacancies to the grain‐boundary core. The space‐charge potentials from the simulations are compared with values obtained by applying the standard, analytical (Mott–Schottky and Gouy–Chapman) expressions. The importance of modelling space‐charge layers from the thermodynamic level is demonstrated.

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“…[10][11][12][13][14][15][16][17]19,[23][24][25][26]28 and is often discussed in terms of spatially varying migration barriers. For example, the vacancy migration barrier strongly depends on the two cations of the tetrahedral edge, which is crossed by an oxide ion during a jump to a nearest neighbor site of the anion sub-lattice: [13][14][15]20,23,26 Refs., 13,14,26 report barriers between 0.3 and 0.67 eV for a Zr-Zr edge and 0.85-1.29 eV for a Y-Zr edge. An increased number of such high barrier edges lowers the effective mobility for increasing doping concentrations.…”

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confidence: 99%

Revisiting the Temperature Dependent Ionic Conductivity of Yttria Stabilized Zirconia (YSZ)

Ahamer

Opitz

Rupp

et al. 2017

J. Electrochem. Soc.

141

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The temperature dependent conductivity of yttria stabilized zirconia (YSZ) exhibits a bending in Arrhenius' plots which is frequently discussed in terms of free and associated oxygen vacancies. However, the very high doping concentration in YSZ leads to such a strong defect interaction that the concept of free vacancies becomes highly questionable. Therefore, the temperature dependent conductivity of YSZ is reconsidered. The conductivity of YSZ with different doping concentration was measured in a broad temperature range. The data are analyzed in terms of two different barrier heights that have to be passed along an average path of an oxygen vacancy in YSZ (two barrier model). For 8-10 mol% yttria, the two barriers are in the range of 0.6 eV and 1.1-1.2 eV, respectively. The conductivity and thus the barrier heights also depend on the cooling rate after a high temperature pre-treatment. This indicates that different frozen-in distributions of dopants affect the vacancy motion by different energy landscapes. Temporarily existing defect configurations, possibly with a strong effect of repulsive oxygen vacancy interaction, are suggested as the reason of high barriers. Future dynamic ab-initio calculations may reveal whether this modified model of the YSZ conductivity is mechanistically meaningful. Yttria stabilized zirconia (YSZ) is among the most important ion conducting solids and acts as a kind of model material representing fast oxide ion conductors. Owing to this model character of YSZ, but also due to its application in solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs) and oxygen sensors, a vast amount of papers can be found dealing with its oxide ion conduction. The ionic conductivity is based on the motion of oxygen vacancies, introduced by Y 3+ ions replacing Zr 4+ . For concentrations above ca. 8 mol%, yttria doping also stabilizes the cubic structure down to room temperature. A detailed review of the science of YSZ and related materials is far beyond the scope of this paper but a few important facts regarding the ionic conductivity of zirconia-based solid electrolytes can be briefly summarized as follows:1-9 i) Doping concentrations above ca. 8 mol% Y 2 O 3 lead to a decrease of the conductivity, despite increasing oxygen vacancy concentration. ii) The conductivity not only depends on the vacancy concentration but also on the kind of dopant. For example, Sc-doped zirconia shows significantly higher conductivity than YSZ. iii) The temperature dependence of the conductivity cannot be described by a single activation energy (E act ) but shows higher E act values at lower temperatures.Numerous theoretical studies were performed in order to understand these experimental observations and to get a deeper insight into defect thermodynamics and kinetics of doped zirconia and of the closely related ceria-based ion conductors, see e.g. Refs. 10-29. Those model studies employed different simulation approaches such as molecular dynamics (MD), density functional theory (DFT) and kinetic Monte Carl...

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A combined DFT + U and Monte Carlo study on rare earth doped ceria

Cited by 117 publications

References 84 publications

Edge dislocation slows down oxide ion diffusion in doped CeO2 by segregation of charged defects

Edge dislocation slows down oxide ion diffusion in doped CeO2 by segregation of charged defects

The grain‐boundary resistance of CeO₂ ceramics: A combined microscopy‐spectroscopy‐simulation study of a dilute solution

Revisiting the Temperature Dependent Ionic Conductivity of Yttria Stabilized Zirconia (YSZ)

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A combined DFT + U and Monte Carlo study on rare earth doped ceria

Cited by 117 publications

References 84 publications

Edge dislocation slows down oxide ion diffusion in doped CeO2 by segregation of charged defects

Edge dislocation slows down oxide ion diffusion in doped CeO2 by segregation of charged defects

The grain‐boundary resistance of CeO2 ceramics: A combined microscopy‐spectroscopy‐simulation study of a dilute solution

Revisiting the Temperature Dependent Ionic Conductivity of Yttria Stabilized Zirconia (YSZ)

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The grain‐boundary resistance of CeO₂ ceramics: A combined microscopy‐spectroscopy‐simulation study of a dilute solution