柔性云母/钙钛矿氧化物体系界面与缺陷的原子尺度研究

Perovskite functional oxides have attracted extensive attentions of research due to their various appealing physical properties. Preparation of epitaxial thin films of perovskite oxides on layered material such as mica is one of the methods to realize flexibility of the film, and has become one of the hot topics in materials research for application in future flexible electron devices. Due to the lack of the detailed research on the interfacial microstructural features, including strain state, atomic structure and defects of the mica/perovskite oxides system, the mechanism for film epitaxy is still veiled. In order to reveal the structural characteristics of the flexible heterostructure system, which is different from conventional rigid film/substrate system, the present project is planned to intensively study series of mica/SrTiO3 films prepared under different growth conditions, by means of aberration-corrected transmission electron microscopy. The efforts of the research will be focused at the crystallographic relationships between the film and the substrate, atomic structure and strain state of the interfaces and domain structure in the films. Based on the experimental results the structure model of the interface will be established, which is the basis for understanding the mechanism for the film epitaxy in the heterostructure system. It is expected that the research results also provide insight into the effect of the microstructures on the properties of the films, and thus provide experimental basis for controlling and tailoring microstructure and thus tuning properties of the flexible films.

钙钛矿功能氧化物具有许多引人注目的物理性质，将其外延生长在层状材料云母基片上从而实现柔性化是目前材料研究的热点之一。然而，对于云母/钙钛矿氧化物体系的微观结构，例如界面的应力状态、原子构型和缺陷类型等，尚知之甚少。因此，对于该系统的外延机理的理解还缺乏实验的支持。为揭示这种有别于传统刚性薄膜/基片结构的柔性异质界面的晶体学特性以及云母/钙钛矿氧化物界面的原子结构，本项目拟以典型的云母/SrTiO3体系作为研究对象，利用球差校正透射电镜的表征手段研究不同生长条件下制备的系列样品。重点研究晶体学取向和畴结构、界面应力状态和原子构型、缺陷类型和分布规律，全方位认知该体系的微观结构。建立界面和缺陷的局域原子构型，理解薄膜初期的形核过程和外延机制。揭示该体系的结构特征与生长条件的关联，阐明结构对物性的影响，为相关柔性薄膜的可控制备、结构裁剪以及性能调控奠定实验基础。

本项目利用先进电子显微学表征手段，对柔性云母外延生长SrTiO3薄膜体系界面的微观结构特性进行了深入研究。该体系存在两种界面结构对应两种晶体学取向关系。低温成长的STO/云母体系界面相对干净敏锐，没有第二相存在，其界面结构由SrTiO3的(111)Sr-O3面和云母基片的(001)(SiAl)2-O3面组成，且二者之间具有较强的相互作用。这两个原子面的氧原子排列具有极高相似性，保证了在特定取向关系下薄膜外延的原子键合环境。界面处的失配位错以及第一性原理计算均表明，这种界面具有较强的原子键合。此外，我们系统研究了自组装PbO结构包裹的PbTiO3纳米复合薄膜。PbTiO3纳米柱状晶粒沿c轴方向承受了巨大的拉应变（13%），导致其晶格四方性达到了c/a = 1.22，远大于相应块体材料数值。实验测得钛—氧原子位移平均值大约为0.052 nm。第一性原理计算证实了实验结果，由此得到的极化值为122 μC/cm2。这有助于理解大应力状态下位移型铁电氧化物的极化增强效应。