Understanding the chemistry at twin boundaries (TB) is a well-recognized challenge, which could enable the capabilities to manipulate the functional properties in complex oxides. The study of this atomic imperfection becomes even more important, as the presence of twin boundaries has been widely observed in materials, regardless of the dimensionalities, due to the complexities in growth methods. In the present study, we provide atomic-scale insights into a ∑3(111̅) ⟨11̅0⟩ twin boundary present in pyrochlore-structured Gd₂Ti₂O₇ using atomic-resolution electron microscopy and atomistic modeling. The formation of the observed TB occurs along (111̅) with a 71° angle between two symmetrically arranged crystals. We observe distortions (∼3 to 5% strain) in the atomic structure at the TB with an increase in Gd–Gd (0.66 ± 0.03 nm) and Ti–Ti (0.65 ± 0.02 nm) bond lengths in the (11̅0) plane, as compared to 0.63 nm in the ordered structure. Using atomistic modeling, we further calculate the oxygen migration barrier for vacancy hopping at 48f–48f sites in the pyrochlore structure, which is the primary diffusion pathway for fast oxygen transport. The mean migration barrier is lowered by ∼25% to 0.9 eV at the TB as compared to 1.23 eV in the bulk, suggesting the ease in oxygen transport through the ∑3 twin boundaries. Overall, these results offer a critical understanding of the atomic arrangement at the twin boundaries in pyrochlores, leading to control of the interplay between defects and properties.

中文翻译：

---

Ʃ3 Gd2Ti2O7烧绿石中的双边界：氧迁移的途径。

理解双边界（TB）处的化学是一个公认的挑战，它可以使人们能够操纵复杂氧化物的功能特性。由于生长方法的复杂性，对原子缺陷的研究变得更加重要，因为在材料中无论尺寸如何，都广泛观察到孪晶边界的存在。在本研究中，我们提供了对烧绿石结构的Gd ₂ Ti ₂ O _7中存在的∑3（111̅）⟨11̅0⟩双晶界的原子尺度见解。使用原子分辨率电子显微镜和原子建模。观察到的TB的形成是沿着（111°）以两个对称排列的晶体之间的71°角发生的。我们观察到，随着（11̅0）平面中Gd–Gd（0.66±0.03 nm）和Ti–Ti（0.65±0.02 nm）键长的增加，TB原子结构的扭曲（约3至5％应变），与有序结构中的0.63 nm相比。使用原子模型，我们进一步计算了烧绿石结构中48f-48f处空位跃迁的氧迁移势垒，这是快速氧气传输的主要扩散途径。与大体积的1.23 eV相比，TB处的平均迁移势垒降低了约25％至0.9 eV，这表明通过∑3双晶界的氧气传输更加容易。总体，