铌酸钾钠基无铅压电薄膜的相结构与压电性能增强机理研究

Owing to the clamping effect, potassium-sodium niobate (KNN) based lead-free piezoelectric thin films typically demonstrate degraded piezoelectric response in comparison with the corresponding ceramics. Thus, it is needed to improve the piezoelectric response in KNN-based thin films. The current proposal tries to enhance the piezoelectricity of KNN-based thin films by creating phase boundaries. Our early results indicate that Li and BaZrO3 doping in KNN-based thin films are effective to modify the monoclinic MC-MA and rhombohedral-MC phase transition temperatures, respectively. The current proposal suggests to adjust the monoclinic MC-MA phase transition temperature to room temperature by Li doping, and tries to realize the phase transition from monoclinic MC to monoclinic MA and the creation of MC-MA phase boundaries at room temperature in KNN-based thin films, which will eventually result in the enhancement of piezoelectric response. Additionally, Li and BaZrO3 co-doping will also been applied in KNN-based thin films to simultaneously adjust the MC-MA and rhombohedral-MC phase transitions, and the rhombohedral-MA phase boundary will be created and the piezoelectric response will be improved as well. The effects of chemical modifications on phase symmetries and the piezoelectricity will be investigated, and we will also try to reveal the relationships between phase symmetries and the piezoelectricity as well as the mechanism to improve the piezoelectric response. This proposal will provide an experimental and theoretical guideline for designing high-performance KNN-based lead-free piezoelectric thin films.

由于受到衬底的束缚，铌酸钾钠(KNN)基无铅压电薄膜的压电常数远小于其块体材料，因此亟需增强KNN基薄膜的压电常数。本项目旨在通过构建相界的方法来实现压电响应的增强。我们前期的研究表明Li元素和BaZrO3掺杂能分别调控KNN基薄膜的单斜MC-MA和菱方-MC相转变温度。本项目提出通过改变Li元素的掺杂量调节单斜MC-MA相转变温度，以实现KNN基薄膜在室温下从单斜MC相转变到单斜MA相，并在室温构建单斜MC-MA相界，提高其压电常数。同时，本项目拟通过Li元素和BaZrO3的共掺同时调控单斜MC-MA和菱方-MC相转变温度，实现在室温构建菱方-MA相界，以进一步提高KNN基薄膜的压电常数。此外，本项目还将研究元素掺杂量对相结构和压电性能的影响，并绘制相图，探究KNN基薄膜的相结构和压电响应之间的相关性，探索压电性能增强机理，为高性能KNN基无铅压电薄膜的组分和结构设计提供实验和理论依据。

压电薄膜是各种微型传感器和驱动器中不可替代的一个重要组成部分，它在微机电系统方面的应用备受关注。铌酸钾钠(KNN)基薄膜是一种前景广阔的无铅压电材料，但是其压电性能有待进一步提高。本项目提出通过多元素掺杂取代及制备工艺优化，探究KNN基薄膜的相结构和畴结构的形成机制，实现KNN基薄膜压电性能的提升。通过BaZrO3和(Bi0.5Li0.5)TiO3的共同掺杂取代和调控薄膜的择优取向实现了KNN基薄膜的压电响应的提升，(100)择优取向的KNN基薄膜的压电响应的增强主要是由于在室温下菱方-正交相界的构建以及非本征压电响应的贡献。在SrTiO3单晶衬底上的KNN外延薄膜具有不同于陶瓷块体材料的单斜MC相，这主要是由于在衬底的束缚下，界面处的KNN外延薄膜发生了显著的A/B位晶格扭曲、氧八面体的倾转和扭曲。以GdScO3为单晶衬底，改变KNN外延薄膜的应变状态，KNN外延薄膜依然为单斜MC相，但是由于KNN外延薄膜在面内的[100]和[010]方向分别受到压应力和拉应力，观察到稳定的头对头和尾对尾的带电畴壁。这些结果有望加深对KNN基材料的理解，同时为KNN基薄膜的实际应用提供一定的实验基础和理论指导。