清華大學材料科學與工程研究院《材料科學論壇》學術報告

報告時間：2023年9月26日上午10:30-12:00

報告人：卓芳平博士（德國達姆施塔特工業大學, 材料與地球科學系）

報告地點：清華大學逸夫技術科學樓B213

邀請人：王轲老師

Dislocation-mediated functionality in bulk ferroelectrics

報告簡介：

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.

報告人簡介：

卓芳平博士， 2018年獲清華大學理學博士學位，2017年在瑞士洛桑聯邦理工學院Dragan Damjanovic教授課題組訪學，2019年至2020年在韓國科學技術研究所(KAIST)物理系Chan-Ho Yang教授課題組擔任博士後研究員，2020年至今在德國達姆斯塔特工業大學材料和地球科學系Jürgen Rödel教授課題組從事研究工作。主要研究興趣包括鐵性材料的缺陷工程和基于機器學習的壓電力顯微鏡技術。主持德國洪堡博士後基金、達姆施塔特工業大學種子基金和德國自然科學基金(Deutsche Forschungsgemeinschaft， DFG)各一項。