钙钛矿氧化物的氧八面体旋转与物性关系的原位应变调控研究

The strongly coupling of multi-freedoms in perovskite oxide introduces numerous novel physical phenomena. Strain engineering on the fine structure and properties of epitaxial perovskite films is of great significance for better understanding the structure-property relationship and exploiting new film devices. In the last round of NSF, we have investigated quantitatively the coupling between lattice constants and properties using synchrotron radiation in situ charactering techniques for the heterojunctions consist of epitaxial films and piezoelectric substrates. Meanwhile, we note that a technical breakthrough for quantitatively measuring the octahedra rotation in perovskite oxide were reported recently, from which people were granted the ability to reveal the important role of bond angle in such materials. Based on above progresses, we intend to do two things for further research: One, studying the oxygen octahedra rotations evolved with external electric field and temperature in typical perovskite manganites and nickelates, thus to disclose the correlation between bond angle, length and transition in electric and magnetic properties at atomic scale. Two, quantitatively analyzing the dependences of in-plane lattice constants of PMNPT substrate on external electric field and orientations, thus to build the microscopic picture of in situ dynamic strain engineering. Our studies will benefit for further understanding of the couplings of intrinsic freedoms in the strongly correlated electron systems as well as the strain engineering technique.

钙钛矿氧化物薄膜中各自由度间的强关联耦合产生了诸多奇异物理效应，研究外延应变对薄膜原子级微观结构及物性的调控，对于深入理解这类材料的结构-物性关系和开发薄膜器件而言非常重要。前期，青年基金项目采用薄膜/压电异质结、同步辐射原位表征等手段系统可靠定量地研究了晶格参数与电磁性质间的关联，取得重要进展；同期，国际上氧八面体旋转角定量测量技术取得突破，人们有能力研究键角等微观结构在物性中扮演的重要角色。基于此，本项目拟在青年基金基础上深入开展两方面工作：以典型钙钛矿锰氧化物和镍氧化物为范例，定量表征异质结中薄膜氧八面体旋转随外电场、温度的变化，探讨键长键角等原子级微观结构与物性上的金属-绝缘体、磁性转变间的关联；定量分析PMNPT衬底面内晶格随外电场的变化及其取向依赖性，构建薄膜/PMNPT异质结原位动态应变调控的微观图像。该研究将加深对强关联电子材料各内禀属性间耦合作用及原位应变调控技术的理解。

钙钛矿氧化物薄膜中各自由度间的强关联耦合产生了诸多奇异物理效应，研究外延应变对薄膜原子级微观结构及物性的调控，对于深入理解这类材料的结构-物性关系和开发薄膜器件而言非常重要。在原青年基金项目(“NSFC11004178:外延(110)钙钛矿锰氧化物膜应变的原位调控及结构-物性关系研究”)的工作基础上，本项目继续开展与原位动态应变调控有关的两方面工作：“PMN-PT原位应变调控的微观机制”、“典型过渡金属氧化物的金属绝缘体转变等宏观性质与微观结构的关联”。. 主要研究内容和重要结果如下：. 发展了同步辐射衍射倒易空间扫描成像技术；运用该技术，定量研究了不同组分、不同取向的PMN-PT单晶在变温和电场作用下的铁弹畴演化，包括极化翻转路径等等，给出PMN-PT原位动态调控异质结中薄膜应变的微观机制；进而设计出更优的原位应变调控路径；证实原位应变调控氧八面体旋转的可行性低。 . 选择含有金属绝缘体转变的典型过渡金属氧化物，包括锰酸盐LaPrCaMnO3，镍酸盐NdNiO3，钒酸盐VO2等，定量研究其晶格应变、氧八面体旋转等微观结构与其宏观电学转变间的关联；研究了SrRuO3氧八面体旋转与其磁易化轴取向的关联。. 这些工作取得了一批学术成果，发表SCI/EI研究论文26篇，培养硕士2名，海内外合作交流20余次，申请国家发明专利1项。