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Anisotropic Chemical Strain in Cubic Ceria due to Oxygen-Vacancy-Induced Elastic Dipoles

Abstract

Accurate characterization of chemical strain is required to study a broad range of chemical-mechanical coupling phenomena. One of the most studied mechano-chemically active oxides, nonstoichiometric ceria (CeO2-δ), has only been described by a scalar chemical strain assuming isotropic deformation. However, the combined Density Functional Theory (DFT) calculations and elastic dipole tensor theory reveal that both the short-range bond distortions surrounding an oxygen-vacancy and the long-range chemical strain are anisotropic in cubic CeO2-δ. The origin of this anisotropy is the charge disproportionation between the four cerium atoms around each oxygen-vacancy (two become Ce3+ and two become Ce4+) when a neutral oxygen-vacancy is formed. Around the oxygen-vacancy, six of the Ce3+-O bonds elongate, one of the Ce3+-O bond shorten, and all seven of the Ce4+-O bonds shorten. Further, the average and maximum chemical strain values obtained through tensor analysis successfully bound the various experimental data. Lastly, the anisotropic, oxygen-vacancy-elastic-dipole induced chemical strain is polarizable, which provides a physical model for the giant electrostriction recently discovered in doped and non-doped CeO2-δ. Together, this work highlights the need to consider anisotropic tensors when calculating the chemical strain induced by dilute point defects in all materials, regardless of their symmetry.

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Publication details

The article was received on 23 Feb 2018, accepted on 14 May 2018 and first published on 14 May 2018


Article type: Paper
DOI: 10.1039/C8CP01219A
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Anisotropic Chemical Strain in Cubic Ceria due to Oxygen-Vacancy-Induced Elastic Dipoles

    T. Das, J. D. Nicholas, B. Sheldon and Y. Qi, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP01219A

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