Department of Applied Physics, Stanford University, Stanford, CA, 94305, USA.
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
Adv Mater. 2023 Apr;35(17):e2210562. doi: 10.1002/adma.202210562. Epub 2023 Mar 19.
Despite extensive studies on size effects in ferroelectrics, how structures and properties evolve in antiferroelectrics with reduced dimensions still remains elusive. Given the enormous potential of utilizing antiferroelectrics for high-energy-density storage applications, understanding their size effects will provide key information for optimizing device performances at small scales. Here, the fundamental intrinsic size dependence of antiferroelectricity in lead-free NaNbO membranes is investigated. Via a wide range of experimental and theoretical approaches, an intriguing antiferroelectric-to-ferroelectric transition upon reducing membrane thickness is probed. This size effect leads to a ferroelectric single-phase below 40 nm, as well as a mixed-phase state with ferroelectric and antiferroelectric orders coexisting above this critical thickness. Furthermore, it is shown that the antiferroelectric and ferroelectric orders are electrically switchable. First-principle calculations further reveal that the observed transition is driven by the structural distortion arising from the membrane surface. This work provides direct experimental evidence for intrinsic size-driven scaling in antiferroelectrics and demonstrates enormous potential of utilizing size effects to drive emergent properties in environmentally benign lead-free oxides with the membrane platform.
尽管在铁电体的尺寸效应方面进行了广泛的研究，但在尺寸减小的反铁电体中，结构和性能如何演变仍然难以捉摸。鉴于反铁电体在高能量密度存储应用中的巨大潜力，了解它们的尺寸效应将为在小尺寸下优化器件性能提供关键信息。在这里，研究了无铅 NaNbO 薄膜中反铁电性的基本内在尺寸依赖性。通过广泛的实验和理论方法，研究了在减小膜厚度时反铁电-铁电转变的有趣现象。这种尺寸效应导致在低于 40nm 的厚度下出现铁电单相，以及在高于此临界厚度时存在铁电和反铁电序共存的混合相状态。此外，结果表明，反铁电和铁电序是可电切换的。第一性原理计算进一步表明，观察到的转变是由膜表面引起的结构变形驱动的。这项工作为反铁电体中内在尺寸驱动的缩尺提供了直接的实验证据，并展示了利用尺寸效应在环境友好的无铅氧化物膜平台上驱动新兴特性的巨大潜力。
