钛酸铋钠基无铅压电陶瓷的缺陷偶极效应和电致应变调控研究

(Bi0.5Na0.5)TiO3 (BNT) is one of the most promising materials as an alternative to toxic lead-based system for the applications of piezoelectric actuators due to its large strain (S) under applied electric field (E). However, the large strain usually requires relatively large electric field excitation, resulting in a low S/E. Moreover, fatigue and hysteresis of strain in these materials have also been a bottleneck impeding the applications. In this project, the defect is introduced in BNT based materials by the donor/acceptor doping in A/B site or annealing under different atmospheres. The formation, switching and drift-diffusion of defect dipoles will be investigated in various phase under different dynamic load, such as electric field, temperature and time. BNT-based materials with high strain and low hysteresis will be achieved by optimizing the volume effect, domain effect, grain boundary effect and the phase structure (average structure and local structure) that induced by defect dipoles. And the interaction mechanism of defect dipoles, structure and strain will be disclosed. Furthermore, the fatigue-free behaviors are to be enhanced by study the different contribution of defect dipoles between ferroelectric phase and nonergodic relaxor phase of BNT during electric cyclings. These will provide fundamental principle and technology supports for the application of BNT based lead-free materials with excellent electric-field-induced strain properties.

钛酸铋钠（BNT）基材料具有大的电致应变，是替代铅基材料用作压电驱动器最具有前途的无铅压电材料体系之一。但是，BNT材料的电致应变需要大电场的触发，使其压电系数（S/E）有待提高，而且存在滞后大、易疲劳等问题，限制了其实际应用。本项目拟通过对BNT基材料进行异价施主/受主掺杂或气氛处理等手段引入缺陷，分析在不同相区内动态负载（电场、温度、时间）对缺陷偶极子形成、翻转及迁移-扩散特征的作用，通过缺陷偶极子的体效应、畴效应、晶界效应以及其对相结构（平均结构和局域结构）的改变协同调控，得到滞后小应变系数大的BNT基材料，揭示缺陷偶极子、结构和应变特性之间的相互作用机理。进一步，研究缺陷偶极子在BNT材料铁电相和遍历弛豫相疲劳过程中的不同行为，优化材料的疲劳特性，为BNT基无铅电致应变材料的应用奠定理论和技术基础。

钛酸铋钠Bi0.5Na0.5TiO3（BNT）是一类重要的无铅钙钛矿压电材料，其特殊弛豫相的结构带来了大的极化和应变。然而，目前缺陷对BNT基材料弛豫相的结构、形成和演化等作用的认识并不充分，极大地影响了其介电、铁电、压电等性能的可调控性。本项目以BNT基材料为研究目标，通过施主、受主及等价掺杂等组分设计，结合气氛烧结等制备手段，研究材料的缺陷结构，揭示了缺陷结构对材料宏观和微观结构的影响，获得了优异的电学性能指标，解析了缺陷-结构-性能之间的关系。取得的主要成果如下：1）通过组分设计和工艺调控，在BNT基材料中引入不同缺陷，分析缺陷及缺陷偶极行为对BNT晶格结构、微观形貌和相结构的影响；2）缺陷引入会使随机场增加，分析了由此带来的材料本征畴结构及在弱场和强场下畴结构的演变，及其对电学特性的影响；3）揭示了缺陷在不同BNT相中调控结构和性能的基本机理，在高弛豫度的相中，获得了在较宽温度范围内具有稳定介电常数的大电致伸缩材料，同时获得了低剩余极化的延迟电滞回线，从而得到了具有优异储能特性的材料体系；在低弛豫相中，缺陷的引入改变了其电致铁电相的结构，得到了低滞后的大应变材料；在铁电相中，缺陷偶极子的形成减小了缺陷的自由移动，使材料的疲劳性能进一步改善。本课题获得的结果对BNT基及其他钙钛矿材料的性能优化及开发设计提供借鉴。