还原气氛烧结对KNN基无铅陶瓷缺陷结构及电学性能影响的研究

The high-performance lead-free piezoelectric materials sintered in reducing atmosphere is very important for preparing the multi-layer piezoelectric devices co-fired with base metal inner electrode. Recently, (K,Na)NbO3 (KNN)-based lead-free piezoelectric ceramics have attracted considerable attention due to their relatively high Curie temperature and piezoelectric properties. However, few researchers could prepare high-performance (K,Na)NbO3 (KNN)-based piezoelectric ceramics in reducing atmosphere until now. This project aims to change the defect structure from oxygen vacancy into relatively stable associated defect by adding the non-equivalent elements and controlling the sintering atmosphere, which could enhance the piezoelectric properties of the ceramics sintered in reducing atmosphere. Microscopic analysis techniques and defect chemistry theory are employed to explore deeply the formation mechanism and migration rule of the defects. Subsequently, the influences of the doping elements, including their coordination number, valence, and ionic radius, as well as sintering atmosphere on the electrical properties of the ceramics are investigated systematically. Based on this, adjust the defect structure and electric properties by controlling the doping elements and sintering atmosphere. And then prepare the KNN-based ceramics with insulation resistivity higher than 1×10^9Ω•m and converse piezoelectric coefficient higher than 400pm/V in reducing atmosphere. The achievements of this project will provide the excellent lead-free piezoelectric materials for the application of the environment-friendly multi-layer piezoelectric devices co-fired with base metal inner electrode.

制备高性能无铅压电抗还原瓷料是贱金属内电极共烧多层陶瓷器件应用的基础和前提，但目前国内外对具有相对较高压电性能和居里温度的铌酸钾钠（KNN）基无铅压电陶瓷体系的还原气氛烧结研究甚少。因此本课题拟通过向KNN体系中添加非等价掺杂元素，同时调控烧结气氛，将陶瓷中容易迁移的氧空位缺陷转变成相对稳定的缔和缺陷，使还原烧结的陶瓷仍具有较高的绝缘电阻和压电活性。借助微观缺陷分析技术和缺陷化学理论，研究缺陷的形成机理和迁移规律，阐释掺杂元素的配位数、化合价、离子半径及烧结气氛等对陶瓷电学性能影响的规律。在此基础上，精细调控陶瓷电学性能和缺陷结构，在还原气氛下烧结出电阻率高于1×10^9Ω•m、2kV/mm电场下的逆压电常数d*33大于400pm/V的KNN基无铅压电陶瓷。为下一步贱金属内电极共烧多层无铅压电陶瓷器件应用提供材料基础。

制备高性能无铅压电抗还原瓷料是贱金属内电极共烧多层陶瓷器件应用的基础和前提。本课题选取具有相对较高压电性能和居里温度的铌酸钾钠（KNN）基无铅压电陶瓷体系为研究对象。主要研究内容和结论如下：（1）等价元素掺杂的KNN基陶瓷在低氧或还原气氛烧结时，氧空位和电子浓度会急剧上升，导致电学性能迅速劣化；（2）当KNN基陶瓷中添加等价掺杂元素，如果陶瓷展示n型导电机制，陶瓷中主要的载流子为电子，随着环境氧分压的降低，陶瓷的电子浓度会随之升高，导致电学性能劣化，因而n型KNN基陶瓷在高氧气氛下性能更优；当KNN基陶瓷中主要载流子为空穴时（即p型KNN基陶瓷），随着环境氧分压的降低，陶瓷的空穴浓度会随之降低，提高陶瓷的绝缘电阻率，进而提高其极化效率和压电性能，因而p型KNN基陶瓷在低氧气氛下性能更优。（3）通过向KNN体系中添加适量的非等价掺杂元素（如Mn、Cu、Sn、Zr、Ba、Ca），使陶瓷呈现p型导电机制，调控陶瓷内部缺陷结构和迁移率，使陶瓷在还原气氛或惰性气氛下仍保持较高的绝缘电阻（高于1×109Ω·m）和压电活性（高于300pC/N）。这为下一步贱金属内电极共烧多层无铅压电陶瓷器件应用提供材料基础。（4）建立一套通过XPS元素价态分析、XRD结构精修、高温阻抗谱、变气氛阻抗谱、霍尔效应测试、TSDC测试、缺陷化学理论等阐释KNN基无铅压电陶瓷中缺陷结构的理论方法，为研究其他功能陶瓷缺陷结构提供更为广泛和深刻的思路。