高电致应变BNT基三元复合无铅压电陶瓷的相变行为与容忍因子关系的研究

(Na0.5Bi0.5)NbO3 (BNT)-based ceramics with giant strain have been received much attention and considered to be a promising environmental-friendly material for lead-free piezoelectric ceramics using as piezoelectric actuators. This application will study the BNT-based ternary system with BaTiO3 and (Bi0.5K0.5)TiO3 as the second composites, and those pervoskite structured components will be used as the third composites. Through changing the compositions of the BNT-based ternary system, morphotropic phase boundary (MPB) of the ternary system will be determined, phase transition behavior at morphotropic phase boundary, and the relationship between the phase structure and electrostrictive properties in the ternary system will be disclosed. Moreover, through the systemic study of the fine structure and domain structure of the compositions in the vicinity of MPB, the structural nature of the MPB will be distinguished, and the correlation between the fine structure, tolerance factor and electrical properties will be discovered. Furthermore, the lattice distortion-field induced strain model will be set up. This application will present the theoretical and experimental support for the exploration of new high-performance lead-free ceramics systems. In addition, compositions lie in MPB regions of the BNT-based ternary system will be further investigated through the approach of texturing. By the composition optimization and the engineering of the microstructural design, samples with the compositions at MPB regions are expected to provide enhanced electrostrictive properties. This application is to find the promising piezoelectric material candidates for practical applications, and lay the foundation for the practical direction of lead-free piezoelectric ceramic.

高电致应变(Bi0.5Na0.5)TiO3(BNT)基无铅压电陶瓷是很有希望在压电驱动器等领域获得应用的环境友好型材料。本项目以BNT基三元复合陶瓷体系为研究对象，选择BaTiO3和(Bi0.5K0.5)TiO3为第二组元，以钙钛矿ABO3型化合物为第三组元，通过改变第二、三组元的种类和含量，寻找三元复合体系的准同型相界(MPB)和新型高电致应变BNT基三元复合陶瓷体系，确定MPB附近组成的相变行为和性能特征，揭示三元体系MPB的组成-容忍因子-电性能之间的内在联系。通过研究BNT基三元复合陶瓷体系的电畴和精细结构，建立精细结构-电致应变关系模型，为探索新型高电致应变BNT基复合体系提供理论和实验支持；同时辅以晶粒定向技术，获得具有相变-晶粒定向双重特征的三元复合陶瓷材料。通过优化材料组分、显微结构和电致应变性能，获得高性能、高可靠性的BNT基材料，为这类无铅压电陶瓷实用化奠定基础。

(Bi0.5Na0.5)TiO3（BNT）基无铅压电陶瓷具有高电致应变和电致伸缩性能，在压电驱动器、高精度位移器等领域具有广泛应用前景，是目前最有希望取代PZT陶瓷的环境友好型材料之一。本项目以BNT基三元系陶瓷为研究对象，以BaTiO3和(Bi0.5K0.5)TiO3为第二组元，以ABO3型钙钛矿为第三组元，通过对材料容忍因子的计算，确立了BNT基陶瓷MPB组分与容忍因子间的半定量关系，MPB组分处材料的容忍因子主要集中在0.980-0.983与0.975-0.976两个范围内，范围的选择与所引入组元的容忍因子相关，揭示了MPB组成-容忍因子-高电致应变之间的内在机理。研究结果表明可从容忍因子预测BNT基材料的MPB组分，为系统快速寻找高电致应变BNT基材料提供全面有效的指导。.对高性能BNT基陶瓷辅以晶粒定向技术，获得较大的[001]取向织构度（>80 %），相比随机取向的陶瓷，织构陶瓷的应变和电致伸缩响应均得到大幅提高。研究了不同钙钛矿模板对BNT-BKT（BT，ST，NN模板）和BNT-KN-ST（BNT，ST模板）陶瓷取向度、相结构、微结构和应变的影响，获得具有相变-晶粒定向双重特征的新型无铅压电陶瓷。在1 mol% BT掺杂的BNT-BKT陶瓷材料中，在45 kV/cm低电场下获得高达0.36 %（Smax/Emax~800 pm/V）的大应变响应。.在BNT-BKT-xST体系中，通过一系列结构和电学性能表征，创新性地构建了电场-温度相图。研究表明，外加电场可在弛豫基质中诱导形成长程铁电序列，且该过程包括两个步骤，即在弛豫相中先形成短程极性团簇，然后极性团簇在外场下进一步形成长程铁电畴。弛豫相与铁电相之间相互转变的临界电场与温度、组分密切相关，该相图为进一步探索BNT基材料的相转变机理提供理论支持。在该体系中，通过调控A位化学计量比获得了高电致应变。研究发现，K、Na元素缺位和Bi元素过量的情况下，可产生~0.4 %的高可逆电致应变。这两种情况下产生的高应变均与组分不均匀性产生的局域无规场有关。基于组分调控的理念，在B位引入(Fe0.5Me0.5)4+（Me=Nb，Sb，Ta）复合离子对，创造性地通过B位组分调控的方式获得了优异温度稳定性的大应变，为BNT基无铅陶瓷的实用化奠定基础。