Dholabhai Pratik P, Martínez Enrique, Brown Nicholas T, Uberuaga Blas Pedro
Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, USA.
Phys Chem Chem Phys. 2017 Aug 30;19(34):23122-23130. doi: 10.1039/c7cp04884j.
In the quest to develop new materials with enhanced ionic conductivity for battery and fuel cell applications, nano-structured oxides have attracted attention. Experimental reports indicate that oxide heterointerfaces can lead to enhanced ionic conductivity, but these same reports cannot elucidate the origin of this enhancement, often vaguely referring to pipe diffusion at misfit dislocations as a potential explanation. However, this highlights the need to understand the role of misfit dislocation structure at semi-coherent oxide heterointerfaces in modifying carrier mobilities. Here, we use atomistic and kinetic Monte Carlo (KMC) simulations to develop a model of oxygen vacancy migration at SrTiO/MgO interfaces, chosen because the misfit dislocation structure can be modified by changing the termination chemistry. We use atomistic simulations to determine the energetics of oxygen vacancies at both SrO and TiO terminated interfaces, which are then used as the basis of the KMC simulations. While this model is approximate (as revealed by select nudged elastic band calculations), it highlights the role of the misfit dislocation structure in modifying the oxygen vacancy dynamics. We find that oxygen vacancy mobility is significantly reduced at either interface, with slight differences at each interface due to the differing misfit dislocation structure. We conclude that if such semi-coherent oxide heterointerfaces induce enhanced ionic conductivity, it is not a consequence of higher carrier mobility.
在开发用于电池和燃料电池应用的具有增强离子电导率的新材料的过程中，纳米结构氧化物受到了关注。实验报告表明，氧化物异质界面可导致离子电导率增强，但这些报告同样无法阐明这种增强的起源，往往含糊地将错配位错处的管道扩散作为一种可能的解释。然而，这凸显了理解半共格氧化物异质界面处错配位错结构在改变载流子迁移率方面所起作用的必要性。在此，我们使用原子和动力学蒙特卡罗（KMC）模拟来建立SrTiO/MgO界面处氧空位迁移的模型，选择该体系是因为错配位错结构可通过改变终止化学来进行调控。我们使用原子模拟来确定SrO和TiO终止界面处氧空位的能量学，然后将其用作KMC模拟的基础。虽然该模型是近似的（如通过选定的推挤弹性带计算所揭示），但它突出了错配位错结构在改变氧空位动力学方面的作用。我们发现，在任一界面处氧空位迁移率均显著降低，由于错配位错结构不同，各界面存在细微差异。我们得出结论，如果此类半共格氧化物异质界面诱导出增强的离子电导率，那并非是载流子迁移率提高的结果。
