多铁性织构陶瓷的微观电、热输运机制研究

Multiferroic ceramics, which can exhibit ferroelectric and magnetic parameter orders simultaneously, have many potential applications because of the multi-controlling characteristic of parameter orders. However, random orientation distributions of composed crystals and the existence of defects in the ceramics impede their excellent ferroic properties. These impedimenta are directly relative to the transportation processes of electricity and heat in nature. Therefore, we will fabricate single-phase and two-phase multiferroic ceramics with textured structures to improve the multiferroic properties and reduce the defects, and then to investigate the micro transportation mechanisms of electricity and heat from the view point of mulitiferroicity dynamics. Four basic aspects are focused in detail on this proposed project. First, we will observe and analyze the microstructure and intrinsic defects, especially focus on the physical and chemical properties of domain (phase) boundaries. Second, we intend to study the dynamic relationship between the microstructure & intrinsic defects and macro multiferroic properties including ferroelectric, magnetic and thermal properties. Third, with help of focused ion beam cutting and piezoresponse force microscopy technics, the characteristics and transportation behaviors of the domain walls and phase boundaries will be observed and detected in situ, respectively, revealing the micro transportation mechanisms of electricity and heat. Fourth, such transportation mechanisms in textured multiferroic ceramics are also planned to be qualitatively or semi-quantitatively described by phenomenological theory and first-principles study. Based on these fundamental studies, it is expected to improve the development multiferroic ceramics in physics and to provide the technic help for the application of multiferroic ceramics.

多铁性陶瓷可以同时具有铁电与铁磁序参量，其独特的多重调控性质在很多领域有广泛的应用前景，但陶瓷的随机晶粒取向及缺陷限制了这些优异性质的发挥。本质上，这些限制与微观电、热输运过程直接相关。因此，拟制备织构化多铁性陶瓷来提高多铁性能并减少缺陷，然后从铁性动力学研究视角出发，研究它们的微观电、热输运机制。具体从几个基本科学问题展开：观察和分析多铁性织构陶瓷的微观结构及缺陷，着重考察畴(相)界面的物理和化学特性；研究这些微观结构及缺陷与宏观铁电铁磁性能及热学性质之间的动力学关联；借助聚焦离子束和压电原子力显微镜等技术手段原位观察和测试畴(相)界面的电、热输运行为，揭示微观电、热输运机理；热力学唯象理论和第一性原理计算从理论上进一步定性或半定量研究多铁性织构陶瓷的微观电、热输运机制。基于对这几个科学问题的研究与探索，期望在丰富多铁性陶瓷研究内涵的同时，为多铁性陶瓷的应用提供技术储备。

多铁性陶瓷因可同时拥有铁电、铁磁、铁弹和铁涡序及多重调控特性而具有广泛的应用前景，但陶瓷中随机取向晶粒抑制了应变及畴的翻转。本项目通过将多铁性陶瓷织构化来提升其铁电、铁磁性能，并借助织构多铁性陶瓷的结构与性能各向异性开展微观电、热输运机制与调控研究。项目团队设计并合成了织构方向平行于自发极化方向的四方钙钛矿和垂直于自发极化方向的铋层状两类织构多铁性陶瓷，在最高织构度大于98%的多铁性陶瓷中完成了如下研究内容：（1）完善了片状模板晶粒的拓扑化学合成技术，阐明了织构多铁性陶瓷的织构化和致密化过程；（2）通过调控织构工艺、掺杂和气氛热处理等手段研究了织构度、应变和缺陷等对织构多铁性陶瓷电、磁、热性能的影响；（3）分析了织构多铁性陶瓷电、磁、热性能的变温演变，提出了铋层状陶瓷中温度场释放应变并增强极化的机制；（4）完成了织构陶瓷热导率的电场调控，发现BaTiO3织构陶瓷在20kV/cm电场下热导率减小28.1%，随机取向陶瓷则仅减小2.5%，通过结构表征和理论分析给出了电畴重取向的热导率调控机制；（5）建立了基于第一性原理、蒙特-卡罗和分子动力学的多尺度变温电、磁、热性能模拟方法，在模型材料BaTiO3和PbTiO3中实现了宽温区内应变、相变、铁电、磁比热和热导率的计算。本项目的工作拓宽了多铁性陶瓷中电、热调控的理论基础，发展了织构化技术使其能广泛应用于多种结构的陶瓷中并显著增强其性能，对促进织构陶瓷的应用具有推动作用。