压电陶瓷基复合材料热错配应力-准同型相变耦合行为及其对压电性能的影响

Piezoelectric matrix composites are the candidate materials in many fields, and the main purpose of the previous studies on the composites have been focused on the improvement of the mechanical properties of the composite to satisfy the requests of applications in the combination properties for the composite. However,the piezoelectric properties of the composite decreases with the inclusion content increasing. The present study is put forward on the basis of following reasons: on the one hand, thermal mismatch stress is the intrinsic feature of compoites. On the other hand, the morphotropic transition of some ABO3 type piezoelectric ceramics is very sensitive to stress, which is the key factor to obtain excellent piezoelectric response of the ceramics. The main aims of the present study are to optimize the piezoelectric properties of piezoelectric ceramic matrix composite and design new type piezoelectric composites on the basis of the coupling model of thermal mismatch stress and morphotropic transition. The materials studied in the present project are oxide particle reinforced Pb(Zr,Ti)O3 or doped BiFeO3 composites. Based on the physical and mathematical models, the critical conditions of morphotropic transition and the coupling behaviors of thermal mismatch stress-morphotropic transition will be investigated. The effect of thermal mismatch stress on the morphotropic transition will be revealed in the view points of both microstructure and mechanics. And the influence roles of thermal mismatch stress and morphotropic phase contents on the piezoelectric properties of the composites will be obtained. Finally, we expect that the results provided in the present study are significant for the enhancement of piezoelectric properties of the composite, and helpful for the designs of new type lead-free piezoelectric materials.

压电陶瓷基复合材料具有广泛的应用背景，以往研究的主要目的是改善其力学性能以适应器件对其综合性能的要求，但其代价是压电性能的劣化。本项目主要依据以下两点，其一是热错配应力是复合材料的内禀属性；其二是某些ABO3钙钛矿型压电陶瓷的准同型相变对应力敏感，而准同型相变是获得优异压电效应的关键。本项目拟通过热错配应力-准同型相变耦合模型的研究，探讨如何利用热错配应力优化复合材料的压电性能，及设计新型压电材料。本项目将以氧化物陶瓷颗粒增强Pb(Zr,Ti)O3和掺杂BiFeO3两类陶瓷基复合材料为对象，通过物理、力学模型的建立，研究复合材料基体准同形相变的条件，探讨热错配应力-准同型相变的耦合行为与机制，从力学和微观两个层面上揭示热错错配应力对准同型相变的影响机理，阐明热错配应力、准同型相含量等对复合材料压电性能的影响规律。最终为提高陶瓷基压电复合材料的压电性能、设计新型无铅压电材料提供依据。

铁电、压电陶瓷与薄膜的制备和性能优化是铁电与压电理论领域的研究重点，如何利用铁电体与压电体特殊电性能在功能器件中发挥重要的作用是该领域科学家最关心的问题，大压电效应的发现与机理的研究是推动压电陶瓷材料发展的核心理论支撑，现有的可获得大压电效应的内在机制都是基于温度(PPT)与组分(MPB)提出的，本项目在特殊掺杂获特殊应力的基础上，极大的提高了压电陶(PZT与BaTiO3)的相关压电性能与温度稳定性，并利用Landau-Ginzburg-Devonshire理论计算获得应力诱导自由能曲面平坦化的程度，设计实验证实了该平坦化的发生，通过物理、力学模型的建立，提供了一种获得大压电效应的掺杂路线，提出了一种获得大压电效应的机制；此外，对BiFeO3基复合薄膜中自极化现象、负电容与大储能密度等铁电性诱发产生的特殊性能进行细致研究，研究自极化现象产生的原因，总结自极化产生的条件。通过理论计算与结构设计，探讨了在BiFeO3基复合薄膜中获得负电容的条件，提出了一种直流偏压辅助模型，并通过实验验证了理论与模型的正确性。同时，探讨多层膜在外场下的电压分配情况，阐明了多层膜的结构对大储能密度的影响规律，本项目在铁电、压电陶瓷与薄膜的理论研究、性能优化与应用拓展等领域开展了一系列的工作，研究结果受到国内外同行认可，目前发表25篇SCI论文，2篇授权专利。