不同气氛烧结KNN基无铅压电陶瓷材料的结构控调与性能的研究

Perovskite Na0.5K0.5NbO3(KNN) based lead-free piezoelectric ceramic materials have been very promising candidates for actuator applications to replace current PZT ceramics due to their good piezoelectric properties and high Curie temperature. However, there are still many unclear fundamental issues in KNN based piezoelectric ceramics such as temperature stable, grain size effect, different atmosphere firing effect and so on. Specially, very few studies were reported on reducing atmosphere fired KNN ceramics, and the effects of low PO2 firing on piezoelectric properties and defects structures in this system are not understood yet. Therefore, deep and systematic fundamental study and comparative investigation will be carried out in this project. On the basis of the applicants’ previous work, we will firstly improve piezoelectric temperature stablility by appropriate modification; Secondly, we will study grain size effect by nanotechnology and using our unique two-step sintering method to accurately control ceramic grain size, exploring the interrelation between the microstructural evolution (fine phase structure, domain structure and local structure) and macroscopic electrical properties (ferroelectric, piezoelectric and strain properties) and relative mechanism. Thirdly, we will study the effects of low PO2 firing in KNN ceramics in terms of composition, microstructures，piezoelectric properties, defects, and reliability. Our aim is to develop high performance KNN ceramic materials which can be sintered in reducing atmosphere in order to cofired with Ni inner electrode, and to design and make a prototype multilayer actuator. The establishment and execution of this project will be expected to provide a solid theoretical and experimental basis for further designing and manufacturing novel lead-free multilayer actuators.

铌酸钾钠（KNN）基无铅压电陶瓷以其较好的压电特性、较高的居里温度，最有希望成为一类新型的无铅压电位移驱动器用陶瓷材料取代现有的PZT陶瓷。针对目前KNN基压电陶瓷材料体系中有关温度特性、晶粒尺寸效应、不同气氛烧结等尚存在的诸多关键科学问题，尤其还原气氛烧结对陶瓷微结构与电学性能影响规律及机理尚不清楚，本项目拟对KNN基压电陶瓷材料进行系统的基础性研究。在前期工作基础上，通过掺杂改性提高该体系的温度稳定特性；通过纳米技术以及独特的两段式无压烧结技术研究晶粒尺寸对微观结构、畴结构影响规律，以及对宏观压电性能的调控机理；通过对还原气氛烧结KNN基压电陶瓷组成、微结构及性能的系统研究，开发出还原气氛烧结高性能KNN基压电陶瓷材料，并设计制备出Ni为内电极的驱动器原型器件。本项目的研究具有重大的科学价值和实际应用的意义，为新型无铅压电陶瓷驱动器的设计及制备提供坚实的科学依据和实验指导。

本项目以不同气氛烧结KNN基无铅压电陶瓷材料的结构调控和性能的研究为内容。系统研究了MnO、ZrO2、CaZrO3等掺杂对不同气氛烧结的KNN基陶瓷结构和性能的影响机制，探讨了改善温度稳定性和提高压电性能的解决方案，并制备具有高位移量和高温度性的多层KNN 基原型器件。设计出四方(T)相和正交(O)相共存的0.96K0.46Na0.54Nb0.98Ta0.02O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3+0.2%mol MnO陶瓷体系，进一步添加CaZrO3来调控该体系的压电性能和温度稳定性。当加入1%CaZrO3时体系获得了最佳的压电性能(d33=300pC/N和25kV/cm下d*33=500pm/V)。CaZrO3含量增加晶粒尺寸减小，导致d*33的温度稳定性由110oC提高到200oC。 研究了不同晶粒尺寸和构成对0.985(0.96K0.46Na0.54Nb0.98Ta0.02O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3)-0.015CaZrO3 +0.2%molMnO体系的结构、压电性能和温度稳定性的影响机制。发现陶瓷(在1180oC和1190oC烧结温度下)的异常长大区域为大量小晶粒包围着大晶粒的模式。这些区域在提高压电性能的同时，有利于缓解d*33温度稳定性恶化。 研究了还原气氛烧结MnO和ZrO2掺杂协调调控0.945K0.48Na0.52Nb0.96Ta0.04O3-0.055BaZrO3+6mol%MnO体系的抗还原特性、耐疲劳、电学性能和温度稳定性机制。1% ZrO2获得了最佳的室温压电性能(20kV/cm下d*33=465pm/V)。材料经过1M次单极应变循环后，d*33劣化程度小于10%。ZrO2可以提高晶界的激活能，改善材料的耐疲劳特性。制备了多层压电器件(尺寸：8.3mm×8.26mm×0.6mm，10层，单层厚度27µm)，其具有高位移输出量(690nm)和高温度稳定性(175oC)。