铌酸钾钠基无铅压电陶瓷抗还原性调控及机理研究

As the piezoelectric devices are developed towards environmental friendly and cost efficiency, lead-free piezoelectric materials and base mental electrodes have become a necessary choice, non-reducible potassium sodium niobate (KNN) based lead-free piezoelectric ceramics are promising to be co-fired with base mental electrodes, which will promote the application of lead-free piezoelectric materials. To solve the problems coming with in co-firing KNN based lead-free piezoelectric materials and nickel electrodes in reduced atmosphere, such as piezoelectric property degradation, toxicity of sintering aids and poor temperature stability, this project proposed to regulate the non-reducibility of KNN piezoelectric materials via doping with rare earth oxides based on material design and to improve the temperature stability based on calculating the energy barrier between orthorhombic and tetragonal phases. The morphotropic phase boundary, oxygen vacancy concentration, vacancy mobility and ferroelectric domains of KNN lead-free piezoelectric materials will be regulated through rare earth doping to improve their non-reducibility and piezoelectric properties. The mechanism of non-reducibility of the rare earth modified KNN will be illustrated using defect chemistry and domain growth models. The energy barrier between orthorhombic and tetragonal phases of KNN lead-free piezoelectric materials will be calculated. The temperature stability will be improved though the optimization of the KNN compositions. The co-firing of non-reducibility of KNN piezoelectric materials and nickel electrodes will be explored. The achievements of this project will provide important principle and mechanism for developing multilayer lead-free piezoelectric devices with base metal electrodes.

随着压电器件向着环境友好和低成本方向发展，压电材料无铅化和电极材料贱金属化成为必然趋势，抗还原性铌酸钾钠（KNN）基无铅压电陶瓷有望实现与贱金属电极共烧，使无铅压电材料走向应用。针对还原气氛下KNN基无铅压电陶瓷与Ni电极共烧中存在的压电性能劣化、助烧剂毒性和温度稳定性差等问题，本项目从材料设计出发，提出了稀土氧化物掺杂调控KNN基无铅压电陶瓷抗还原性、基于KNN两相间势垒计算提升温度稳定性。主要开展KNN晶体结构和缺陷结构的第一性原理计算，通过稀土氧化物掺杂协同调控准同型相界、氧空位浓度及其迁移率和铁电畴，获得具有抗还原性和高压电活性的KNN基无铅压电陶瓷，结合缺陷化学分析和铁电畴生长模型，揭示其抗还原机理；通过计算KNN正交相和四方相之间的势垒指导组分优化进而提升其温度稳定性；探索抗还原性KNN基无铅压电材料与Ni电极匹配共烧，为开发贱金属电极多层无铅压电器件奠定理论和技术基础。

随着压电器件向着环境友好和低成本方向发展，压电材料无铅化和电极材料贱金属化成为必然趋势，抗还原性铌酸钾钠（KNN）基无铅压电陶瓷有望实现与贱金属电极共烧，使无铅压电材料走向应用。针对还原气氛下KNN基无铅压电陶瓷与Ni电极共烧中存在的压电性能劣化、助烧剂毒性和温度稳定性差等问题，本项目进行了KNN无铅压电陶瓷抗还原性研究，KNN基及含KNN体系无铅压电陶瓷组分优化及性能提升，抗还原性KNN基多层压电陶瓷及器件研究。主要结果如下：.（1）还原气氛下烧结的KNN陶瓷中含有较多氧空位和弱束缚电子，表现出异常高的介电常数和损耗。随着后退火温度的升高，陶瓷中的氧空位逐渐得到补偿，弱束缚电子浓度降低，陶瓷介电性能逐渐恢复正常。经过900 ℃后退火后，集中在陶瓷晶界氧空位基本补偿完全，陶瓷的压电系数d33为112 pC/N，平面机电耦合系数kp为0.37，逆压电系数d33*为149 pm/V，与普通空气烧结的KNN陶瓷性能相近。 .（2）通过加入CTN烧结助剂，促进在烧结过程中液相的产生，使陶瓷晶粒尺寸分布更加均匀，其中Cu以Cu+离子的形式存在于陶瓷内部。当CTN含量为1 wt%时，陶瓷的压电系数d33为131 pC/N，平面机电耦合系数kp为0.43，逆压电系数d33*为307 pm/V，实现了抗还原性KNN基无铅压电陶瓷性能提升。采用高通量制备方法，揭示BNT-BT-KNN三元体系中三方铁电(I)、弛豫铁电(II)和四方铁电(III)的相区分布特征，并获得了该体系的三元性能相图。.（3）相对于压片成型，流延成型的生坯微观结构疏松，烧结过程中碱金属挥发更明显，陶瓷在高温段的介电损耗较高，但不同成型工艺的陶瓷压电性能相差不大；制备出Ni电极KNN基多层压电陶瓷器件，陶瓷基体与电极之间结合紧密，两者之间无元素扩散或反应，当外加400 V电压时，多层器件的应变为0.05%。.综上所述，本项目揭示了KNN无铅压电陶瓷的抗还原性机理，开发了性能提升的抗还原性KNN基以及含KNN的无铅压电陶瓷材料，实现了抗还原性KNN基无铅压电陶瓷与Ni电极匹配共烧，为贱金属电极多层无铅压电器件的开发和生产奠定了理论和技术基础。 .