Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200062, People's Republic of China.
J Phys Condens Matter. 2013 Apr 24;25(16):165901. doi: 10.1088/0953-8984/25/16/165901. Epub 2013 Apr 3.
We report a systematic theoretical study on the ferroelectric behavior of ultrathin three-component ferroelectric films, e.g., CaTiO3-BaTiO3-SrTiO3, sandwiched between electrodes. Using first-principles calculations we demonstrate that such structures have intrinsic asymmetric ferroelectricity which is robust even at the nanoscale. In addition, there exists a certain relationship between the polarization directions and geometric stacking sequences of the superlattices. Specifically, the lowest energy states always have polarizations pointing from CaTiO3 via BaTiO3 to SrTiO3, while the sequence in the metastable states is SrTiO3-BaTiO3-CaTiO3. Therefore we were able to distinguish one ferroelectric state from its opposite state by means of their geometric stackings along the polarization directions. Besides this, band alignment analysis reveals that such structures are well behaved at the metal/ferroelectric interface, confirming the credibility and reliability of our first-principles calculation. Our finding may suggest a controllable and unambiguous way to build ferroelectric and multiferroic tunnel junctions.
我们对夹在电极之间的超薄三组分铁电薄膜（例如 CaTiO3-BaTiO3-SrTiO3）的铁电行为进行了系统的理论研究。通过第一性原理计算，我们证明了这些结构具有内在的非对称铁电性，即使在纳米尺度上也是如此。此外，超晶格的极化方向和几何堆积序列之间存在一定的关系。具体而言，最低能量状态始终具有从 CaTiO3 通过 BaTiO3 指向 SrTiO3 的极化，而亚稳态的顺序是 SrTiO3-BaTiO3-CaTiO3。因此，我们能够通过沿极化方向的几何堆积来区分铁电状态与其相反状态。除此之外，能带排列分析表明，此类结构在金属/铁电界面处表现良好，证实了我们第一性原理计算的可信度和可靠性。我们的发现可能为构建铁电和多铁隧道结提供了一种可控且明确的方法。
