多层压电致动器用铁电-弛豫复合陶瓷性能调控与电致大应变机理

Multilayer piezoelectric actuator has a wide application due to the advantages of high-precise displacement, high-speed response and large blocking force. BNT based ergodic relaxors exhibiting giant electric-field-induced strains are promising candidates for application in high-strain actuators. However, this giant strain requires very high electric field and exhibits very large strain-hysteresis. Ferroelectric-relaxor ceramic composites are proposed to reduce this electric field and hysteresis, the ferroelectric grains will be added to relaxor matrix to increase the electric field distribution in relaxor matrix, facilitate the phase transition from PNRs to ferroelectric state as well as stabilize the induced ferroelectric domains. Moreover, the texturing will also be employed to reduce the driving field and strain hysteresis. The distributions and ratio of ferroelectric/relaxor grains, grain orientation as well as the sintering process are designed and well controlled to optimize the microstructures of composite ceramics. The effects of inhomogeneous electric-field, local field, fine phase structures and interfacial stress on lattice strain, phase transition and domain switching will also be systematically studied. Furthermore, by using PFM, in-situ TEM, in-situ high-energy XRD and in-situ neutron diffraction, the planned project will investigate the polarization-coupling and strain-coupling effects between ferroelectric and relaxor phases to reveal the mechanisms for field-induced phase transition. The models and empirical formulas for electric-field-induced phase transition, domain switching, and the field-induced strain will be proposed for the composite ceramics with various inhomogeneous electric-field and local field. The proposed project will provide a new insight for designing and preparing of a new generation high-performance lead-free piezoceramics and multilayer actuators.

多层压电致动器因精度高、响应快、驱动力大而广泛应用，BNT基弛豫铁电体具有极高的电致应变，是制造致动器的绝佳选择，但是应变所需驱动电场太高、迟滞过大。项目提出在弛豫体中加入铁电相制备铁电-弛豫陶瓷基复合材料，由于介电和成分的不均匀使外加电场在复合陶瓷中非均匀分布，铁电相也促进和稳定了弛豫相中生成的铁电畴，使相变在更低电场下完成，结合织构化工艺，有效减小驱动电场和迟滞。通过调控两相几何分布、配比、晶粒取向和互扩散以优化复合陶瓷微结构，揭示非均匀电场、局域电场、相结构和晶界应力对晶格应变、相转变和电畴翻转的影响机制。结合PFM、原位TEM、高能XRD和中子衍射等技术，深入研究铁电相和弛豫相之间的力电耦合效应，揭示极化耦合和应变耦合效应增强的低电场下大电致应变机理，建立不同非均匀场和局域电场下电致相变、电畴翻转与电致应变的理论模型与经验公式。为设计和制备高性能无铅压电材料和器件提供实验理论依据。

钛酸铋钠（BNT）基弛豫铁电陶瓷是一类很有应用前景的材料。它的商业化主要面临两个难题：一是需要非常高的驱动电场（>6kV/mm）才能激发出大的应变，商用要求是低于3kV/mm；二是存在较大的应变迟滞（>50%），会降低器件的使用精度。本项目首先采用了离子取代和弛豫/铁电复合的手段，在BNT基无铅陶瓷中获得了低驱动电场大应变无铅陶瓷体系，特别是将BNT-25ST陶瓷的驱动电场降低到了3kV/mm，达到了市场对材料驱动电场的要求。接着利用织构化方法进一步提高了体系的性能，而且对已有的大电致应变BNT基陶瓷的烧结特性做出了重要改进。然后设计并制备出了BNT基无铅多层压电致动器，该器件在680V的驱动电压下可产生0.3%的大应变和5μm的位移，并且表现出良好的循环稳定性，在工业应用中具有广阔的应用前景。最后结合原位技术，揭示了弛豫/铁电复合陶瓷中极化耦合和应变耦合效应的物理机制。本项目的成功实施对无铅压电陶瓷材料及其在多层致动器方面的应用起到了积极推进作用，并且丰富了铁电、压电学科相关的物理理论知识。