Jeong Jeehun, Hwang Jaejin, Xing Yaolong, Wang Zhipeng, Lee Jaekwang, Oh Sang Ho
Department of Energy Engineering, KENTECH Institute for Energy Materials and Devices, Korea Institute of Energy Technology (KENTECH), Naju, 58330, Republic of Korea.
Department of Physics, Pusan National University, Busan, 46241, Republic of Korea.
Adv Sci (Weinh). 2025 Apr;12(16):e2412781. doi: 10.1002/advs.202412781. Epub 2025 Feb 13.
The interplay between surface reconstruction and depolarization of ferroelectric oxide surfaces is strongly influenced by oxygen vacancies (V). Using in-situ atomic-resolution electron microscopy imaging and spectroscopy techniques, it is directly observed that a clean BaTiO (001) surface stabilizes into (2 × 1) BaO-terminated reconstruction during vacuum annealing. This surface reconstruction is achieved with accommodating BaO deficiency and incorporates TiO adunits. The cooperative atomic rumpling in both the surface and subsurface layers, arranged in a tail-to-tail configuration, is stabilized by planar accumulation of V in the subsurface TiO layer. This reduces the net polarization of surface unit cells, contributing to overall depolarization. Under this atomic rumpling, the polarization-down (P↓) state is energetically favored over the polarization-up (P↑) state, as the P↓ state requires less atomic relaxation in the bulk layers to achieve dipole inversion at the subsurface. The energetic preference for V in the subsurface TiO layer of the P↓ state is confirmed through calculations of V formation energy and the energy barrier for surface-to-subsurface migration. These findings reveal that the presence of V in the subsurface layer lifts the degeneracy in the double-well potential between the P↓ and P↑ states in BaTiO (001).
铁电氧化物表面的表面重构与去极化之间的相互作用受到氧空位（V）的强烈影响。使用原位原子分辨率电子显微镜成像和光谱技术，直接观察到清洁的BaTiO（001）表面在真空退火过程中稳定为（2×1）BaO端接重构。这种表面重构是通过容纳BaO缺陷并结合TiO亚单元来实现的。表面层和次表面层中以尾对尾构型排列的协同原子起伏，通过次表面TiO层中V的平面堆积而稳定。这降低了表面晶胞的净极化，导致整体去极化。在这种原子起伏下，极化向下（P↓）状态在能量上比极化向上（P↑）状态更有利，因为P↓状态在体层中需要较少的原子弛豫来实现次表面的偶极反转。通过计算V形成能和表面到次表面迁移的能垒，证实了P↓状态下次表面TiO层中V的能量偏好。这些发现表明，次表面层中V的存在消除了BaTiO（001）中P↓和P↑状态之间双阱势的简并性。
