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Understanding Chemical Expansion in Non-Stoichiometric Oxides: Ceria and Zirconia Case Studies

Authors

  • Dario Marrocchelli,

    Corresponding author
    1. Laboratory for Electrochemical Interfaces, Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
    Current affiliation:
    1. School of Chemistry Trinity College Dublin, Dublin 2, Ireland
    • Laboratory for Electrochemical Interfaces, Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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  • Sean R. Bishop,

    Corresponding author
    1. International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, Nishi-ku Fukuoka 819-0395, Japan
    2. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
    • International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, Nishi-ku Fukuoka 819-0395, Japan
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  • Harry L. Tuller,

    Corresponding author
    1. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
    • Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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  • Bilge Yildiz

    Corresponding author
    1. Laboratory for Electrochemical Interfaces, Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
    • Laboratory for Electrochemical Interfaces, Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Abstract

Atomic scale computer simulations, validated with experimental data, are used to uncover the factors responsible for defect-induced chemical expansion observed in non-stoichiometric oxides, exemplified by CeO2 and ZrO2. It is found that chemical expansion is the result of two competing processes: the formation of a vacancy (leading to a lattice contraction primarily due to electrostatic interactions) and the cation radius change (leading to a lattice expansion primarily due to steric effects). The chemical expansion coefficient is modeled as the summation of two terms that are proportional to the cation and oxygen radius change. This model introduces an empirical parameter, the vacancy radius, which can be reliably predicted from computer simulations, as well as from experimental data. This model is used to predict material compositions that minimize chemical expansion in fluorite structured solid oxide fuel cell electrolyte materials under typical operating conditions.

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