Guo Haizhong, Zhao Ruiqiang, Jin Kui-Juan, Gu Lin, Xiao Dongdong, Yang Zhenzhong, Li Xiaolong, Wang Le, He Xu, Gu Junxing, Wan Qian, Wang Can, Lu Huibin, Ge Chen, He Meng, Yang Guozhen
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China.
ACS Appl Mater Interfaces. 2015 Feb 4;7(4):2944-51. doi: 10.1021/am508511y. Epub 2015 Jan 23.
Varying the film thickness is a precise route to tune the interfacial strain to manipulate the properties of the multiferroic materials. Here, to explore the effects of the interfacial strain on the properties of the multiferroic BiFeO3 films, we investigated thickness-dependent structural and polarization evolutions of the BiFeO3 films. The epitaxial growth with an atomic stacking sequence of BiO/TiO2 at the interface was confirmed by scanning transmission electron microscopy. Combining X-ray diffraction experiments and first-principles calculations, a thickness-dependent structural evolution was observed from a fully strained tetragonality to a partially relaxed one without any structural phase transition or rotated twins. The tetragonality (c/a) of the BiFeO3 films increases as the film thickness decreases, while the polarization is in contrast with this trend, and the size effect including the depolarization field plays a crucial role in this contradiction in thinner films. These findings offer an alternative strategy to manipulate structural and polarization properties by tuning the interfacial strain in epitaxial multiferroic thin films.
改变薄膜厚度是精确调节界面应变以操控多铁性材料性能的途径。在此，为探究界面应变对多铁性BiFeO₃薄膜性能的影响，我们研究了BiFeO₃薄膜厚度依赖的结构和极化演变。通过扫描透射电子显微镜证实了在界面处具有BiO/TiO₂原子堆积序列的外延生长。结合X射线衍射实验和第一性原理计算，观察到从完全应变的四方性到部分弛豫的四方性的厚度依赖结构演变，且无任何结构相变或旋转孪晶。BiFeO₃薄膜的四方性（c/a）随薄膜厚度减小而增加，而极化则与该趋势相反，并且包括去极化场在内的尺寸效应在较薄薄膜的这种矛盾中起关键作用。这些发现为通过调节外延多铁性薄膜中的界面应变来操控结构和极化性能提供了一种替代策略。
