Department of Materials Science and Engineering and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Nat Commun. 2016 Aug 31;7:12572. doi: 10.1038/ncomms12572.
Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden-Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure.
层状复合氧化物通过多种内置设计旋钮（如拓扑结构、化学有序方案和结构的几何调整）提供了一个异常丰富的材料平台，用于涌现现象。通过调整层尺寸（n）和应变，可以预测在 Ruddlesden-Popper（RP）、An+1BnO3n+1 薄膜中存在多种极性相竞争；然而，目前还没有这种竞争状态的直接原子尺度证据。在 Sr n+1Ti nO3n+1 薄膜中使用具有亚埃分辨率的校正像差扫描透射电子显微镜，我们证明了反铁电、铁电和新的有序和低对称相的共存。我们还直接观察到了岩盐层的原子起伏，这是 RP 结构中导致竞争相的关键特征；电子显微镜和密度泛函理论之间表现出了极好的定量一致性。该研究表明，通过具有不同现象的高度竞争相，层状拓扑结构可以实现多功能性。
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