Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 20, Issue 22, Pages 15293-15299Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c8cp01219a
Keywords
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Funding
- National Science Foundation [DMR-1410946, DMR-1410850]
- NSF CAREER Award [CBET-1254453]
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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-delta), has only been described by a scalar chemical strain assuming isotropic deformation. However, 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-delta. 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-delta. 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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