Kim Jeong Rae, Jang Jinhyuk, Go Kyoung-June, Park Se Young, Roh Chang Jae, Bonini John, Kim Jinkwon, Lee Han Gyeol, Rabe Karin M, Lee Jong Seok, Choi Si-Young, Noh Tae Won, Lee Daesu
Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 08826, Korea.
Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Korea.
Nat Commun. 2020 Oct 2;11(1):4944. doi: 10.1038/s41467-020-18741-w.
Nonequilibrium atomic structures can host exotic and technologically relevant properties in otherwise conventional materials. Oxygen octahedral rotation forms a fundamental atomic distortion in perovskite oxides, but only a few patterns are predominantly present at equilibrium. This has restricted the range of possible properties and functions of perovskite oxides, necessitating the utilization of nonequilibrium patterns of octahedral rotation. Here, we report that a designed metastable pattern of octahedral rotation leads to robust room-temperature ferroelectricity in CaTiO, which is otherwise nonpolar down to 0 K. Guided by density-functional theory, we selectively stabilize the metastable pattern, distinct from the equilibrium pattern and cooperative with ferroelectricity, in heteroepitaxial films of CaTiO. Atomic-scale imaging combined with deep neural network analysis confirms a close correlation between the metastable pattern and ferroelectricity. This work reveals a hidden but functional pattern of oxygen octahedral rotation and opens avenues for designing multifunctional materials.
非平衡原子结构能够在其他方面均为常规的材料中呈现出奇异且与技术相关的特性。氧八面体旋转在钙钛矿氧化物中形成了一种基本的原子畸变，但在平衡状态下主要仅存在少数几种模式。这限制了钙钛矿氧化物可能具备的特性和功能范围，因此有必要利用八面体旋转的非平衡模式。在此，我们报告称，一种设计出的八面体旋转亚稳模式在CaTiO₃中导致了稳健的室温铁电性，而CaTiO₃在其他情况下直至0 K都是非极性的。在密度泛函理论的指导下，我们在CaTiO₃的异质外延薄膜中选择性地稳定了这种与平衡模式不同且与铁电性协同的亚稳模式。原子尺度成像结合深度神经网络分析证实了亚稳模式与铁电性之间存在紧密关联。这项工作揭示了氧八面体旋转一种隐藏但具有功能性的模式，并为设计多功能材料开辟了道路。
