1. 报告题目: Structural origin of electric properties of BiFeO3-BaTiO3 solid solutions
报告人：陈建国 教授
单位：上海大学
报告时间：2023年11月11日星期六下午 14:00
报告地点：知新楼C1104
邀请人：王春明 教授
报告摘要：The chemical distribution, local phase constitutions and domain configurations of BiFeO3-BaTiO3 ceramics with different overall phases (pseduo-cubic PC, rhombohedral R and coexistence of PC and R) were carefully studied to understand structural mechanisms of the piezoelectric properties. Universal cores (inner core and outer core)-rim structures in grains are detected in all the compositions, its concentration decrease with BF content. The inner cores in all compositions show the dominant R phase, and their domain size increases with the BF content. The rims change from dominant PC phase with polymorphic polar nanoregions (PNRs) (x=0.64) to coexistence of R and PC with PNRs and nanodomain (x=0.7) and then to dominant R phase with PNRs+macrodomain (x=0.75). The inner core with R phase and rim with higher domain wall density and the coexistence of local rhombohedral and tetragonal symmetries are responsible for the high and thermal-stable electric-field induced strain in the PC phase, and furthermore the small domain sizes as well as high clamping stress at the core-rim interfaces result in a flexible and reversible phase transition from PNRs to macrodomains under electric field. Our results evidence the decisive contribution of the composition-modulated hierarchical microstructures to the high and thermal stable electric-field induced strain, and are anticipated to provide the necessary foundation for the effective modulation of the piezoelectricity from structural perspectives.
2. 报告题目：Understanding the strain mechanisms in BiFeO3-BaTiO3 piezoelectric ceramics near the morphotropic phase boundary
报告人：陈建国 教授
单位：上海大学
报告时间：2023年11月12日星期日上午 10:00
报告地点：知新楼C1104
邀请人：王春明 教授
报告摘要：BiFeO3-BaTiO3 (BF-BT) solid solution is one of the most interesting lead-free candidates for piezoelectric actuator applications. However, the underlying strain mechanism remains unclear. In this work, the origins of the unipolar strain, strain hysteresis and remnant strain of Mn-modified BF-BT ceramics near the pseudo-cubic and rhombohedral (PC-R) phase boundary, before and after poling treatments, were investigated by high-energy synchrotron X-ray diffraction. The largest unipolar strain of BF-BT ceramics was found to occur at the composition with single pseudo-cubic phase, rather than the phase boundary composition, owing to the synergetic contributions from the reversible phase transition of PC-R phase, non-180o domain switching and lattice distortion. It is interesting to find that the phase boundary composition exhibit an irreversible PC-R phase transition, where its unipolar strain after poling is attributed to the lattice distortion. The lowest strain hysteresis and remnant strain were observed in BF-BT ceramics with rhombohedral phase, due to the fact that the reversible lattice distortion dominates the strain level. These new findings in BF-BT solid solutions are expected to provide a new sight on strain mechanisms of perovskite-structured ferroelectric materials.
报告人介绍：陈建国，上海大学材料科学与工程学院教授，博士生导师，澳洲伍伦贡大学高级访问学者，Journal of Advanced Dielectrics和Crystals期刊青年编委。主持国家自然科学基金面上项目1项，青年项目1项，上海市自然基金面上项目1项，重点实验室开放基金2项，横向课题3项；作为研究骨干参与国家自然科学基金面上项目、上海市地方高校重大项目及等项目。从事铁电、压电材料组分设计、制备及器件开发领域的基础研究，在Acta materialia, Nano energy、Energy conversion and management、Journal of the European ceramics society、Journal of the American ceramics society、Applied physics Letters、Journal of Applied Physics等学术刊物发表学术论文140余篇，SCI引用2400余次，H因子27。授权国家发明专利8项。
