铌酸钾钠基压电陶瓷铁电畴的纳米结构调控及其与相界协同作用对陶瓷压电性能的增强机制

In order to further improve properties of potassium-sodium niobate lead-free piezoelectric ceramics, the project would tightly center on relations between microstructure (nano domain and phase boundary) and macro physical properties and methods based on the combination of experimental research and theoretical simulation are employed to carry on following study: deep discussion of indispensable factors to influence domain’s structure so as to illuminate formation mechanism of nano domain which is closely related to grain size, dopants and types of ferroelectric phase; deep discussion of domain motion and interactive coupling both of which are tightly associated with domain structure, and effects of the interaction on related macro physical properties of the ceramics so as to clarify the mechanism of property strengthen of the ceramics which is closely connected with essential laws of domain motion; deep discussion of relations between nano domians and phase boundary so as to elaborate the mechanism of enhanced properties of the ceramics in the view of the cooperation effects of them in the case of considering comprehensive influences of each of them on piezoelectric properties. Based on research results of the project, the aim of significant property improvement of potassium-sodium niobate lead-free piezoelectric ceramics through microstructure modification, would be expected to be realized, and some valuable theoretical basis would also be provided for property design of KNN-based ceramics. Meanwhile, the project provides helpful reference for mechanism researches and design as well as development of other perovskite-type lead-free systems.

为了进一步提升铌酸钾钠基无铅压电陶瓷的性能，本项目拟围绕陶瓷微结构（纳米铁电畴与相界）与宏观物理性能之间的关联，采用实验研究与理论计算相结合的手段，系统地展开以下研究：深入研究决定电畴结构的主要因素，阐明与晶粒尺寸、掺杂离子及铁电晶型有关的纳米铁电畴形成机理；深入研究与电畴结构密切相关的畴壁运动及其耦合机制、畴间交互作用对陶瓷关联物性的影响，阐明畴壁运动的基本规律及其对陶瓷性能的增强作用；建立纳米铁电畴和多晶相界的关联，并综合考虑二者对陶瓷宏观压电性能的影响，阐明其协同作用对KNN基无铅压电陶瓷压电性能的增强作用。基于本项目的研究结果，实现通过微结构的调整，有效提升铌酸钾钠基无铅压电陶瓷性能的目标，并为有针对性地实现铌酸钾钠基无铅压电陶瓷的性能设计提供一定的理论基础。同时，为其他钙钛矿结构无铅体系的机理研究和材料设计及开发，提供有价值的参考。

铌酸钾钠基无铅压电陶瓷被认为是有望取代铅基压电陶瓷的重要候选材料之一，但性能的提升正经历一个瓶颈期。本项目以铌酸钾钠基陶瓷为研究对象，针对该类陶瓷的“纳米结构调控及其与相界协同作用”及与之相关的“陶瓷压电性能的增强机制”两个关键科学问题开展一系列研究，并取得了一些有价值的研究成果。通过四年的努力，取得的主要成果如下：.(1)铌酸钾钠基压电陶瓷铁电畴的纳米结构调控.首先从理论的角度验证了纳米铁电畴的偏转较为容易，源于较小的纳米铁电畴壁和畴壁能，称之为铁电畴的尺寸效应，并根据铁电畴的形成及畴壁能的起源，综合考虑电畴表面电荷的极性和纳米铁电畴的尺寸，对纳米铁电畴的尺寸效应进行了定量描述。然后采用掺杂改性的手段，构建多晶相界的同时，采用“冻结”晶粒的生长的方式，获得具有纳米铁电畴结构的铌酸钾钠基陶瓷，并基于密度泛函理论（DFT）计算了不同掺杂元素的特征能带结构及其导致的KNN晶格形变过程，初步阐明了铌酸钾钠基压电陶瓷纳米铁电畴的形成机理，并将以上研究结果反馈于材料设计及制备工艺的调整，基本实现了铌酸钾钠基压电陶瓷铁电畴的纳米结构调控。.(2)纳米铁电畴与相界协同作用对陶瓷压电性能的增强机制.通过微结构表征或分析软件模拟纳米铁电畴应力场或电场分布情况，了解了不同类型纳米铁电畴的产生过程及可能的偏转方式，并研究了纳米铁电畴在外场下的畴变过程及电畴纳米尺度的耦合机制、纳米铁电畴及其畴壁运动对电畴关联物性（陶瓷应变及矫顽场）的影响、陶瓷性能的增强机理等。.经过四年的系统研究，以上两个研究要点基本按计划执行完成。本项目获得了一系列性能优良的KNN基压电陶瓷（最佳性能：d33 ~570 pC/N，kp ~60%）和一些新型的材料设计理念，有望5-10年应用于压电传感器、压电滤波器等领域。