报告摘要：

Dislocations are 1D topological defects  that exert control over composition, strain, and charge at extended  length scales. They offer an additional means to tailor thermal and  electrical conductivity beyond the limitations imposed by traditional  bulk doping. In contrast to atomistic doping, the dislocation  structure is stable to several hundred degree Celsius. In the case of  ferroelectrics, dislocations act as nucleation sites for domain  formation and serve as pinning centers for the motion of domain walls,  which are 2D topological defects. However, the potential of extended  dislocations in bulk ferroelectrics has been widely underestimated.  Furthermore, uniaxial plastic deformation can induce irreversible and  elastic strain fields in ferroelectrics, allowing for the permanent  tailoring of elastic energy. This means that dislocations possess the  capability to impart strain modifications to bulk ferroelectrics.

In this talk, my focus will be on a  novel approach to manipulate the mobility of ferroelectric domain  walls and piezoelectricity of single-crystal BaTiO3. Specifically, we  achieved a 19-fold increase in the converse piezoelectric coefficient  by imprinting dislocations via high-temperature creep along the [001]  direction. By employing controlled high-temperature plastic  deformation along the [110] direction, we successfully optimized the  dielectric and electromechanical properties of the material. This  optimization was achieved by leveraging the anisotropic interactions  between 1D dislocations and 2D domain walls. Time permitting, we will  discuss the domain instability and extrinsic degradation processes  that can both be mitigated during the aging and fatigue with a careful  strain tuning of the ratio of in-plane and out-of-plane domain  variants. Intrinsic strain engineering in bulk ferroelectrics  highlights the potential of plastic deformation as a means to tailor  the microstructure and functionality of ferroelectrics. Texture will  be quantified using nuclear paramagnetic resonance (Dr. Pedro  Grosczewicz) and temperature dependent domain evolution will be  revealed using in-situ transmission electron microscopy (group of  Xiaoli Tan). If accessible, I may report on options to introduce  dislocations into polycrystalline oxides in general and ferroelectrics specifically.

报告人简介：

卓芳平博士，2018年获清华大学理学博士学位，2017年在瑞士洛桑联邦理工学院Dragan Damjanovic教授课题组访学，2019年至2020年在韩国科学技术研究所(KAIST)物理系 Chan-Ho Yang教授课题组担任博士后研究员，2020年至今在德国达姆斯塔特工业大学材料和地球科学系Jürgen R?del教授课题组从事研究工作。主要研究兴趣包括铁性材料的缺陷工程和基于机器学习的压电力显微镜技术。主持德国洪堡博士后基金、达姆施塔特工业大学种子基金和德国自然科学基金(Deutsche  Forschungsgemeinschaft，DFG)各一项。