Zhang Ningbin, Zhu Yinlian, Li Da, Pan Desheng, Tang Yunlong, Han Mengjiao, Ma Jinyuan, Wu Bo, Zhang Zhidong, Ma Xiuliang
Shenyang National Laboratory for Materials Science, Institute of Metal Research , Chinese Academy of Sciences , Wenhua Road 72 , 110016 Shenyang , China.
School of Material Science and Engineering , University of Science and Technology of China , 230026 Hefei , China.
ACS Appl Mater Interfaces. 2018 Nov 7;10(44):38230-38238. doi: 10.1021/acsami.8b13674. Epub 2018 Oct 29.
Oxygen vacancy configurations and concentration are coupled with the magnetic, electronic, and transport properties of perovskite oxides, and manipulating the physical properties by tuning the vacancy structures of thin films is crucial for applications in many functional devices. In this study, we report a direct atomic resolution observation of the preferred orientation of vacancy ordering structure in the epitaxial LaCoO (LCO) thin films under various strains from large compressive to large tensile strain utilizing scanning transmission electron microscopy (STEM). Under compressive strains, the oxygen vacancy ordering prefers to be along the planes parallel to the heterointerface. Changing the strains from compressive to tensile, the oxygen vacancy planes turn to be perpendicular to the heterointerface. Aberration-corrected STEM images, electron diffractions, and X-ray diffraction combined with X-ray photoelectron spectroscopy demonstrate that the vacancy concentration increases with increasing misfit strains and vacancy distribution is more ordered and homogeneous. The temperature-dependent magnetization curves show the Curie temperature increases, displaying a positive correlation with the misfit strains. With change in the strain from compressive to tensile, anisotropy fields vary and show large values under tensile strains. It is proposed that oxygen vacancy concentration and preferred ordering planes are responsible for the enhanced magnetic properties of LCO films. Our results have realized a controllable preparation of oxygen vacancy ordering structures via strains and thus provide an effective method to regulate and optimize the physical properties such as magnetic properties by strain engineering.
氧空位构型和浓度与钙钛矿氧化物的磁性、电子性质及输运性质相关联，通过调控薄膜的空位结构来操纵其物理性质对于许多功能器件的应用至关重要。在本研究中，我们利用扫描透射电子显微镜（STEM）报道了在从大压缩应变到拉伸应变的各种应变条件下，外延LaCoO（LCO）薄膜中空位有序结构择优取向的直接原子分辨率观察结果。在压缩应变下，氧空位有序排列倾向于沿着与异质界面平行的平面。将应变从压缩应变改变为拉伸应变时，氧空位平面变为垂直于异质界面。像差校正STEM图像、电子衍射以及结合X射线光电子能谱的X射线衍射表明，空位浓度随着错配应变的增加而增加，并且空位分布更有序且均匀。温度依赖的磁化曲线表明居里温度升高，与错配应变呈正相关。随着应变从压缩应变变为拉伸应变，各向异性场发生变化，并且在拉伸应变下显示出较大的值。有人提出氧空位浓度和择优有序平面是LCO薄膜磁性能增强的原因。我们的结果通过应变实现了氧空位有序结构的可控制备，从而提供了一种通过应变工程来调节和优化诸如磁性能等物理性质的有效方法。
