Defect structures in doped CeO2 studied by using XAFS spectrometry

Yamazaki, Satoshi; Matsui, Tsuneo; Ohashi, Toyo; Arita, Yuji

doi:10.1016/s0167-2738(00)00569-5

Cited by 89 publications

(96 citation statements)

References 13 publications

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“…Beyond the second coordination shell, the relaxations are rather small. The relaxation patterns that we have calculated are consistent with recent extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) spectroscopy measurements, which show that upon doping with trivalent ions, the CeOO interatomic distances decrease (18). In agreement with experiments, we also predict the size of this decrease to be smaller for an increasing atomic number of the lanthanide elements (18).…”

Section: Resultssupporting

confidence: 90%

Optimization of ionic conductivity in doped ceria

Andersson

Simak

Skorodumova

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

481

392

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Oxides with the cubic fluorite structure, e.g., ceria (CeO2), are known to be good solid electrolytes when they are doped with cations of lower valence than the host cations. The high ionic conductivity of doped ceria makes it an attractive electrolyte for solid oxide fuel cells, whose prospects as an environmentally friendly power source are very promising. In these electrolytes, the current is carried by oxygen ions that are transported by oxygen vacancies, present to compensate for the lower charge of the dopant cations. Ionic conductivity in ceria is closely related to oxygen-vacancy formation and migration properties. A clear physical picture of the connection between the choice of a dopant and the improvement of ionic conductivity in ceria is still lacking. Here we present a quantum-mechanical first-principles study of the influence of different trivalent impurities on these properties. Our results reveal a remarkable correspondence between vacancy properties at the atomic level and the macroscopic ionic conductivity. The key parameters comprise migration barriers for bulk diffusion and vacancy-dopant interactions, represented by association (binding) energies of vacancy-dopant clusters. The interactions can be divided into repulsive elastic and attractive electronic parts. In the optimal electrolyte, these parts should balance. This finding offers a simple and clear way to narrow the search for superior dopants and combinations of dopants. The ideal dopant should have an effective atomic number between 61 (Pm) and 62 (Sm), and we elaborate that combinations of Nd͞Sm and Pr͞Gd show enhanced ionic conductivity, as compared with that for each element separately. density functional theory ͉ diffusion ͉ point defects ͉ solid oxide fuel cells ͉ CeO 2 M aterials providing high conductivity of oxygen ions are urged by a number of important technological applications, such as oxygen sensors and solid oxide fuel cells (1). The latter are expected to become high-efficiency electrical power generators that enable clean energy production and support sustainable development (2-4). A standard electrolyte for solid oxide fuel cell applications is yttria-stabilized zirconia (YSZ) (1, 5). To increase the ionic conductivity of YSZ to a technologically useful level, high operating temperatures (Ϸ1,000°C) are required. Lowering of the operating temperatures would considerably increase the applicability and competitiveness of solid oxide fuel cells. The ionic conductivity ( ) can be expressed as an exponential function of the activation energy for oxygen vacancy diffusion (E a ),where T stands for temperature, k B for the Boltzman constant, and 0 for a temperature-independent prefactor. Materials with lower E a will facilitate ionic conductivity at lower temperatures, and here rare-earth doped ceria is one of the main candidates (1, 4). The basic principle for the choice of a dopant, advocated by many researchers, is the ability of the dopant to minimize the internal strain of the lattice (6-8). Clear understanding of the phys...

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Section: Resultssupporting

confidence: 90%

Optimization of ionic conductivity in doped ceria

Andersson

Simak

Skorodumova

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

481

392

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“…The local structural environment of fluorite-based ionic conductors has been evaluated for different authors by using EXAFS spectroscopy. Fortunately for our purposes, most of these studies were focused on YSZ [40][41][42] and CGO [9][10][11]. Figure 4(a) and (b) shows the comparison between our simulations (high temperature regime) and the reported EXAFS experiments (all of them obtained at room temperature).…”

Section: Oxygen Diffusion and Cation-oxygen Average Distancesmentioning

confidence: 99%

“…Only few measurement techniques can be employed to study the required local environments or distortions and relaxations of the lattice. Techniques such as diffuse scattering [7,8], extended X-ray absorption fine structure (EXAFS) spectroscopy [9][10][11] conductivity relaxation measurements [12,13], nuclear magnetic resonance (NMR) spectroscopy [14,15], quasi-elastic light scattering [12,16], europium fluorescence spectroscopy [17,18] or tracer diffusion experiments [19,20] have been employed but the yielded data are not sufficient and difficult to interpret, particularly at high temperatures. It is for these reasons that computer modelling has become a popular way to understand the disorder associated with fast ionic conductors [21].…”

Section: Introductionmentioning

confidence: 99%

A Molecular Dynamics Study on the Oxygen Diffusion in Doped Fluorites: The Effect of the Dopant Distribution

et al. 2011

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The effect of the dopant distribution on the oxygen diffusion in doped fluorites typically used for solid oxide fuel cells electrolyte applications has been analysed by using molecular dynamics simulations. The oxygen mass transport in both yttria‐stabilized zirconia (YSZ) and gadolinia‐doped ceria has been studied and compared in the range of temperatures between 1,159 and 1,959 K. A new methodology based on the analysis of local environments is used to describe the diffusion process at an atomic scale. Preferred vacancy migration pathways, most suitable conduction models, energy landscapes and jump efficiency have been detailed for each material. Finally, a particular case of non‐random distribution of dopants in YSZ is presented in order to quantitatively evaluate the effect of the dopant pattern on the mass transport properties and the potential of the methodology developed here for understanding and foreseeing real configurations at the nanoscale.

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“…One way to confirm the defect cluster configurations is to use localized probes such as the synchrotron-based extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopic analyses to examine the local cation coordination [29,30]. Alternatively, electron beam-based techniques such as high-resolution electron energy loss spectroscopy (EELS) and selected-area electron diffraction (SAED) can be used [31].…”

Section: ð9:1þmentioning

confidence: 99%

Oxygen Ion‐Conducting Materials

Хартон

Marques

Kilner

et al. 2009

Solid State Electrochemistry I

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Oxygen ionic and mixed ionic-electronic conductors find important applications in solid-state electrochemical devices, including sensors, solid oxide fuel cells, hightemperature electrolyzers, and oxygen separation membranes. This chapter presents a brief overview of oxide phases with high diffusivity of O 2À anions, providing an introduction to this fascinating topic. Particular emphasis is centered on the comparative analysis of ionic and electronic conductivity variations in the major groups of solid oxide electrolytes and mixed conductors, such as perovskite-and fluorite-related compounds, apatite-type silicates, and derivatives of g-Bi 4 V 2 O 11 and b-La 2 Mo 2 O 9 . The defect chemistry mechanisms relevant to the oxygen ion migration processes are briefly discussed. IntroductionTechnologies based on the use of high-temperature electrochemical cells with oxygen anion-or mixed-conducting ceramics provide important advantages with respect to the conventional industrial processes [1][2][3][4][5][6][7][8]. In particular, solid oxide fuel cells (SOFCs) are considered as alternative electric power generation systems due to high energy-conversion efficiency, fuel flexibility, and environmental safety [1][2][3]. Dense ceramic membranes with mixed oxygen-ionic and electronic conductivity have an infinite theoretical separation factor with respect to oxygen, and can be used for gas separation and the partial oxidation of light hydrocarbons [4,5,7,8] (these and other applications are reviewed in Chapters 12 and 13). For all types of electrochemical cells, the key properties which determine the use of a material are the partial ionic and electronic conductivities. As an example, solid electrolytes for SOFCs, oxygen pumps and electrochemical sensors should exhibit a maximum oxygen ionic conductivity, while the electronic transport should be minimal. In contrast, for SOFC electrodes Solid State Electrochemistry I: Fundamentals, Materials and their Applications. Edited by Vladislav V. Kharton

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Defect structures in doped CeO2 studied by using XAFS spectrometry

Cited by 89 publications

References 13 publications

Optimization of ionic conductivity in doped ceria

Optimization of ionic conductivity in doped ceria

A Molecular Dynamics Study on the Oxygen Diffusion in Doped Fluorites: The Effect of the Dopant Distribution

Oxygen Ion‐Conducting Materials

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