Anisotropic chemical strain in cubic ceria due to oxygen-vacancy-induced elastic dipoles
Anisotropic chemical strain in cubic ceria due to oxygen-vacancy-induced elastic dipoles
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DOI：
10.1039/c8cp01219a
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发表时间：
2018-06-14
影响因子：
3.3
通讯作者：
Qi, Yue
中科院分区：
文献类型：
--
作者：
Das, Tridip;Nicholas, Jason D.;Qi, Yue
化学应变的准确表征是研究广泛的化学-力学耦合现象所必需的。研究最多的机械化学活性氧化物之一，非化学计量铈（CeO2-delta），只能用假设各向同性变形的标量化学应变来描述。然而，密度泛函理论（DFT）和弹性偶极张量理论的联合计算表明，在立方ceo2 - δ中，围绕氧空位的短程键畸变和远程化学应变都是各向异性的。这种各向异性的起源是当中性氧空位形成时，每个氧空位周围的四个铈原子（两个变成Ce3+，两个变成Ce4+）之间的电荷歧化。在氧空位周围，6个Ce3+-O键拉长，1个Ce3+-O键缩短，7个Ce4+-O键全部缩短。此外，通过张量分析得到的化学应变平均值和最大值成功地结合了各种实验数据。最后，各向异性、氧空位-弹性-偶极子诱导的化学应变是极化的，这为最近在掺杂和未掺杂CeO2-delta中发现的巨电致伸缩提供了一个物理模型。总之，这项工作强调了在计算所有材料中由稀释点缺陷引起的化学应变时，无论其对称性如何，都需要考虑各向异性张量。
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.