无电滞后钛酸铋钠基电致伸缩陶瓷的结构调控及其机理研究

Environmental-friendly (Na0.5Bi0.5)TiO3 (BNT)-based electrostrictors generally exhibit good electrostrictive properties comparable with that of traditional Pb-based electrostrictors near the morphotropic phase boundary (MPB). However, the materials suffer from large strain hysteresis, which will greatly limit the application of the materials using in mechatronic field. Therefore, special attention should be paid to reduce the hysteresis of BNT-based electrostrictors for their applications. In this project, BNT-based ternary systems with the other pervoskite structured components or metallic oxides are prepared. Through changing the compositions of the BNT-based ternary system, the MPB of the ternary system will be determined. Based on the MPB composition, high-performance BNT-based electrostrictors without hysteresis will be achieved by further phase structure adjustment and the engineering of the microstructural design, which includes enhancement of crystal symmetry of MPB composition, and control of grain size via two-step sintering approach, spark plasma sintering method, and so on. Moreover, through the systemic study of the influences of phase structure, grain size and domain structure on the electrostrictive properties, and the interaction mechanism of all kinds of structural factors influencing the electrostrictive effect, the origin of purely electrostrictive behavior in the compositions based on the MPB will be disclosed. This application is to present the theoretical and experimental support for the exploration of high-performance BNT-based lead-free electrostrictors, and lay the foundation for the practical direction of these materials.

(Bi0.5Na0.5)TiO3(BNT)基无铅电致伸缩陶瓷在准同型相界(MPB)附近具有与铅基材料相媲美的电致应变和电致伸缩响应，但其电滞后现象严重，限制了这类环境友好型材料在精密机械电子等领域上的应用。因此，解决BNT基电致伸缩陶瓷的电滞后问题，对促进其应用具有重要的意义。本申请拟以BNT基三元陶瓷体系为研究对象，通过调整所添加钙钛矿结构组元或金属氧化物的种类和含量，构筑三元陶瓷体系的MPB，提高MPB附近材料的晶体结构对称性；再结合两步烧结、放电等离子体烧结等工艺控制陶瓷晶粒尺寸，设计和开发出高性能、无电滞后BNT基电致伸缩陶瓷材料。在此基础上，研究不同组成BNT基陶瓷的晶体结构、晶粒尺寸和电畴结构等对电致伸缩性能的影响；探索影响材料电滞后行为各种结构因素之间的相互作用规律，揭示基于MPB组成高性能、无滞后电致伸缩行为产生的机理，为BNT基无铅电致伸缩陶瓷的应用奠定理论与技术基础。

本项目针对(Bi0.5Na0.5)TiO3 (BNT)基无铅电致伸缩陶瓷在准同型相界(MPB)附近电滞后现象严重的研究现状，提出通过相结构和显微形貌的协同调控，设计和开发高性能、无滞后BNT基电致伸缩材料的思路。通过本项目的实施，我们得到了如下结论：1）以准同型相界MPB组分0.80Bi0.5Na0.5TiO3-0.20Bi0.5K0.5TiO3 (简写为BNKT20) 和0.94Bi0.5Na0.5TiO3-0.06BaTiO3 (简写为BNBT6)作为基础配方，以金属氧化物或ABO3钙钛矿型化合物作为外加组元，对基体材料实施相结构调控，进而获得电致应变性能（Smax/Emax > 450pm/V）可以与传统铅基材料相媲美的BNT基材料。更为重要的是，所获得材料的抗疲劳特性非常优异：当电场循环106次时，材料的电致应变性能几乎无改变，相比于其他含铅材料以及其他类无铅压电材料，材料的耐疲劳特性明显提高。2）在上述高电致应变BNT基组成的基础上，沿着MPB线，通过进一步增大所添加组元的含量，获得晶体结构高度对称的“立方”相，进而制备出无电滞后现象的BNT基电致伸缩材料。实验结果显示，所制备出的无电滞后行为的BNT基电致伸缩材料室温附近的电致伸缩系数Q33 > 0.02m4/C2，同时材料兼具温度稳定优(20oC~160oC)和耐疲劳特性好(106次)的特点。通过对上述材料进行精细结构研究，发现无滞后电致伸缩行为产生源于高度对称的“立方相”结构、细小的晶粒尺寸以及极性纳米微区，它们共同抑制电场作用下畴的转向，进而实现“无滞后”行为。该类材料的研制及机理方面的探索将为其在精密机械电子等领域上的应用奠定基础，并一定程度上推动电子元件“无铅化”的实施。3）此外，本项目在设计BNT基电致伸缩材料的同时，尝试引入稀土离子获取BNT基电致伸缩材料的荧光效应，并重点研究电致伸缩和荧光效应之间的耦合作用，实现了电致伸缩材料的多功能化，这对于研发新型光电器件起到一定的推动作用。