†Laboratory for Electrochemical Interfaces, Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
‡Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
J Am Chem Soc. 2015 Apr 15;137(14):4735-48. doi: 10.1021/ja513176u. Epub 2015 Apr 3.
The effect of dislocations on the chemical, electrical and transport properties in oxide materials is important for electrochemical devices, such as fuel cells and resistive switches, but these effects have remained largely unexplored at the atomic level. In this work, by using large-scale atomistic simulations, we uncover how a ⟨100⟩{011} edge dislocation in SrTiO3, a prototypical perovskite oxide, impacts the local defect chemistry and oxide ion transport. We find that, in the dilute limit, oxygen vacancy formation energy in SrTiO3 is lower at sites close to the dislocation core, by as much as 2 eV compared to that in the bulk. We show that the formation of a space-charge zone based on the redistribution of charged oxygen vacancies can be captured quantitatively at atomistic level by mapping the vacancy formation energies around the dislocation. Oxide-ion diffusion was studied for a low vacancy concentration regime (ppm level) and a high vacancy concentration regime (up to 2.5%). In both cases, no evidence of pipe-diffusion, i.e., significantly enhanced mobility of oxide ions, was found as determined from the calculated migration barriers, contrary to the case in metals. However, in the low vacancy concentration regime, the vacancy accumulation at the dislocation core gives rise to a higher diffusion coefficient, even though the oxide-ion mobility itself is lower than that in the bulk. Our findings have important implications for applications of perovskite oxides for information and energy technologies. The observed lower oxygen vacancy formation energy at the dislocation core provides a quantitative and direct explanation for the electronic conductivity of dislocations in SrTiO3 and related oxides studied for red-ox based resistive switching. Reducibility and electronic transport at dislocations can also be quantitatively engineered into active materials for fuel cells, catalysis, and electronics.
位错对氧化物材料的化学、电学和输运性质的影响对于电化学器件（如燃料电池和电阻开关）非常重要，但这些影响在原子水平上仍然很大程度上未被探索。在这项工作中，我们通过使用大规模原子模拟，揭示了 SrTiO3 中 ⟨100⟩{011} 刃型位错如何影响局部缺陷化学和氧离子输运。我们发现，在稀溶液极限下，SrTiO3 中氧空位形成能在离位错核较近的位置更低，与体相相比低 2 eV。我们表明，通过映射位错周围的空位形成能，可以在原子水平上定量捕获基于带电氧空位再分布的空间电荷区的形成。我们研究了低空位浓度（ppm 级）和高空位浓度（高达 2.5%）两种情况下的氧离子扩散。在这两种情况下，根据计算的迁移势垒，都没有发现管道扩散（即氧离子迁移率显著提高）的证据，这与金属中的情况相反。然而，在低空位浓度下，由于空位在位错核的积累，导致扩散系数增加，尽管氧离子迁移率本身低于体相。我们的发现对于信息和能源技术中钙钛矿氧化物的应用具有重要意义。在 SrTiO3 及相关氧化物中，观察到的位错核处较低的氧空位形成能为基于氧化还原的电阻开关研究中观察到的位错电子导电性提供了定量和直接的解释。位错的可还原性和电子输运也可以定量设计到燃料电池、催化和电子学等活性材料中。
