LiTaO3压电陶瓷结构缺陷的多角度调控机制及其压电性研究

Lithium metatantalate (LiTaO3) is a widely piezoelectric and ferroelectric crystal, but the LiTaO3 ceramic was rare reported. Some oxides can promote the sintering process, but the lower piezoelectric properties of LiTaO3 matrix ceramics is attributed to non-ferroelectic phase and the pinning of domain walls caused by point defect due to ion doped. In this study, multi-valence manganese were added to LiTaO3 ceramic matrix in order to improve the piezoelectric and sintering properties of LiTaO3 ceramics with multi-angle, such as reduce lattice distortion, consume point defects, formation neutral defect complex and promote the sintering process. The influence of composition, phase structure and sintering process on piezoelctric properties will be studied, and structure regulation mechanisms of defect and ferroelectric domain will be revealed. The purpose of this project is to establish the relationship between defect, domain structure and electrical properties. A ferroelectric domain switching model was created by introducing the defect and impurity ions and to develop the novel way to obtain the good sintering and piezoelectric properties. The objective of this project is to pioneering new research and application areas of LiTaO3 matrix piezoelectric ceramic. It has important scientific significance and potential engineering application and be expected to get a new lead-free piezoelectric ceramics.

LiTaO3是应用很普遍的铁电和压电晶体，因其烧结性差很少作为压电陶瓷材料来研究。一些氧化物虽然能促进其烧结成型，但非铁电相的存在以及LiTaO3压电陶瓷内的点缺陷钉扎畴壁现象使其压电性能不高。本项目采用多变价Mn元素从晶格畸变、消耗点缺陷、形成中性缺陷复合体、促进烧结多角度同时改善其烧结性与压电性能；通过改变组成、相结构和烧结工艺，研究不同组成和制备工艺对压电性能的影响规律，揭示结构缺陷与铁电畴结构调控机制；研究外场下各种结构缺陷和铁电畴的响应行为，建立该材料缺陷结构、电畴结构与电学性能的本质关联，创建引入缺陷和杂质离子后铁电畴翻转模型，发展出获得良好烧结性和压电性的LiTaO3压电陶瓷的新方法。本项目的实施对开拓LiTaO3基压电陶瓷新的研究和应用领域具有重要的科学意义及潜在的工程应用价值，并有望获得一种新的无铅压电陶瓷材料。

LiTaO3晶体很少作为陶瓷材料来研究，因其颗粒难烧结且介电压电性能不高。本项目制备了LiTaO3基MnO2/LiTaO3复合陶瓷，系统研究了烧结工艺和LiTaO3晶粒内的电畴结构、力学性能和电学性能，并对以往制备的Al2O3/LiTaO3复合陶瓷压电性能进行了研究，揭示了电畴形成机理并构建其结构模型。主要结果如下：(1) 无压烧结制备的LiTaO3基陶瓷烧结致密度最大值达到93.1%。热压烧结制备的LiTaO3基陶瓷致密度最大值达到98.6%。LiTaO3基陶瓷的致密度和硬度都随MnO2含量的增加先增加后减小。(2) LiTaO3晶粒内部电畴结构清晰可见，其SEM形貌为台阶式特征。基体LiTaO3颗粒均匀，第二相均匀地分布于基体的晶界上。(3) 周围颗粒或第二相颗粒的强烈约束使得MLT和ALT陶瓷复合材料中出现了LiTaO3单晶中不可能形成的非180o电畴结构。这种非180o电畴结构属于孪晶面为( 02)的孪晶结构，电畴畴界两边的自发极化夹角为67o。(4) 在不同的频率下随着MnO2含量的增加材料的介电常数和介电损耗都增加，但是少量MnO2(3wt.%)的添加既能增加材料的介电常数同时又降低了材料的介电损耗。随着MnO2含量的增加MLT陶瓷复合材料的介电损耗在一定温度范围内也是逐渐增加的。(5) ALT压电复合陶瓷的压电常数大约为LiTaO3晶体的20%-30%，最大值为5×10-12C/N，达到LiTaO3单晶的50%。MLT复合陶瓷的压电性能因极化处理过程中发生击穿现象无法测出。对LiTaO3基压电陶瓷的研究对开拓陶瓷材料新的研究和应用领域，具有重要的科学意义并有望获得一种新的无铅压电陶瓷材料。本项目添加可变价的锰元素采用传统的无压烧结掺杂制备LiTaO3基陶瓷材料，使制备工艺简化、成本降低，在工业上将有良好的应用前景。