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The Concentration and Diffusivity of Oxygen Interstitials in Niobia-Doped Ceria

Waldow, Stephan and Wardenga, Hans and Beschnitt, Stefan and Klein, Andreas and De Souza, Roger A. (2019):
The Concentration and Diffusivity of Oxygen Interstitials in Niobia-Doped Ceria.
In: The Journal of Physical Chemistry C, ACS Publications, pp. 6340-6350, 123, (11), ISSN 1932-7447,
DOI: 10.1021/acs.jpcc.8b10613,
[Online-Edition: https://doi.org/10.1021/acs.jpcc.8b10613],
[Article]

Abstract

We studied the behaviour of oxygen interstitials in donor-doped ceria using equilibrium conductivity measurements, conductivity relaxation experiments and (18O2 / 16O2) isotope exchange experiments. Equilibrium conductivities and conductivity relaxation experiments were performed in the oxygen activity range 10-6 ≤ aO2 ≤ 10-1 at temperatures of 923 K, 973 K and 1023 K. Oxygen isotope exchanges were carried out at 673 ≤ T / K ≤ 1073 at an oxygen activity of aO2 = 0.2, and oxygen isotope profiles in the solid were obtained by Secondary Ion Mass Spectrometry (SIMS). Analysis of the measured equilibrium conductivities with a defect-chemical model yielded the incorporation enthalpy and entropy of oxygen interstitials. Values of the chemical diffusion coefficient of oxygen (from relaxation experiments) and of the tracer diffusion coefficient of oxygen (from isotope exchange experiments) were converted into diffusion coefficients of oxygen interstitials using the defect-chemical model. Based on these data, the activation enthalpy of oxygen-interstitial migration in Ce0.99Nb0.01O2+δ was found to be (1.28 ± 0.13) eV. Strong enrichment of Si, Ca and Al at the surfaces of the ceramic samples prevented the determination of surface exchange coefficients that refer to donor-doped ceria.

Item Type: Article
Erschienen: 2019
Creators: Waldow, Stephan and Wardenga, Hans and Beschnitt, Stefan and Klein, Andreas and De Souza, Roger A.
Title: The Concentration and Diffusivity of Oxygen Interstitials in Niobia-Doped Ceria
Language: English
Abstract:

We studied the behaviour of oxygen interstitials in donor-doped ceria using equilibrium conductivity measurements, conductivity relaxation experiments and (18O2 / 16O2) isotope exchange experiments. Equilibrium conductivities and conductivity relaxation experiments were performed in the oxygen activity range 10-6 ≤ aO2 ≤ 10-1 at temperatures of 923 K, 973 K and 1023 K. Oxygen isotope exchanges were carried out at 673 ≤ T / K ≤ 1073 at an oxygen activity of aO2 = 0.2, and oxygen isotope profiles in the solid were obtained by Secondary Ion Mass Spectrometry (SIMS). Analysis of the measured equilibrium conductivities with a defect-chemical model yielded the incorporation enthalpy and entropy of oxygen interstitials. Values of the chemical diffusion coefficient of oxygen (from relaxation experiments) and of the tracer diffusion coefficient of oxygen (from isotope exchange experiments) were converted into diffusion coefficients of oxygen interstitials using the defect-chemical model. Based on these data, the activation enthalpy of oxygen-interstitial migration in Ce0.99Nb0.01O2+δ was found to be (1.28 ± 0.13) eV. Strong enrichment of Si, Ca and Al at the surfaces of the ceramic samples prevented the determination of surface exchange coefficients that refer to donor-doped ceria.

Journal or Publication Title: The Journal of Physical Chemistry C
Volume: 123
Number: 11
Publisher: ACS Publications
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Electronic Structure of Materials (ESM)
Date Deposited: 01 Mar 2019 07:26
DOI: 10.1021/acs.jpcc.8b10613
Official URL: https://doi.org/10.1021/acs.jpcc.8b10613
Funders: The authors acknowledge funding from the Deutsche Forschungsgemeinschaft (DFG) from projects SO 499/7-1 and KL 1225/7-1.
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