Xu Xianghan, Huang Fei-Ting, Qi Yubo, Singh Sobhit, Rabe Karin M, Obeysekera Dimuthu, Yang Junjie, Chu Ming-Wen, Cheong Sang-Wook
Rutgers Center for Emergent Materials, Rutgers University, Piscataway, NJ, USA.
Department of Physics & Astronomy, Rutgers University, Piscataway, NJ, USA.
Nat Mater. 2021 Jun;20(6):826-832. doi: 10.1038/s41563-020-00897-x. Epub 2021 Jan 25.
HfO, a simple binary oxide, exhibits ultra-scalable ferroelectricity integrable into silicon technology. This material has a polymorphic nature, with the polar orthorhombic (Pbc2) form in ultrathin films regarded as the plausible cause of ferroelectricity but thought not to be attainable in bulk crystals. Here, using a state-of-the-art laser-diode-heated floating zone technique, we report the Pbc2 phase and ferroelectricity in bulk single-crystalline HfO:Y as well as the presence of the antipolar Pbca phase at different Y concentrations. Neutron diffraction and atomic imaging demonstrate (anti)polar crystallographic signatures and abundant 90°/180° ferroelectric domains in addition to switchable polarization with negligible wake-up effects. Density-functional-theory calculations indicate that the yttrium doping and rapid cooling are the key factors for stabilization of the desired phase in bulk. Our observations provide insights into the polymorphic nature and phase control of HfO, remove the upper size limit for ferroelectricity and suggest directions towards next-generation ferroelectric devices.
氧化铪是一种简单的二元氧化物，具有可超大规模集成到硅技术中的铁电性。这种材料具有多晶型性质，超薄薄膜中的极性正交（Pbc2）形式被认为是铁电性的可能原因，但人们认为在块状晶体中无法实现。在这里，我们使用先进的激光二极管加热浮区技术，报告了块状单晶HfO:Y中的Pbc2相和铁电性，以及不同Y浓度下反极性Pbca相的存在。中子衍射和原子成像表明存在（反）极性晶体学特征以及丰富的90°/180°铁电畴，此外还有可切换的极化，且唤醒效应可忽略不计。密度泛函理论计算表明，钇掺杂和快速冷却对于在块状材料中稳定所需相是关键因素。我们的观察结果为氧化铪的多晶型性质和相控制提供了见解，消除了铁电性的尺寸上限，并为下一代铁电器件指明了方向。
