钙钛矿碱金属铌酸盐铁电体缺陷特性与宏观电学性质关联性研究

The correlation between defects and macroscopic electrical properties of ferroelectrics is one of the most interesting topics in the field of ferroelectric and piezoelectric materials. Our previous results show that Cu-doping imposes a strong hardening effect on the KNN ceramics, making them exhibit an extra-ordinary high mechanical quality factor, double-loop-like characteristics and special aging effects. However, the understanding of the origin of special electrical properties in Cu-doped KNN is still very incomplete. In this work, we will apply the electron paramagnetic resonance spectroscopy, positron annihilation technique and PFM/TEM using the combination of static and dynamic methods as well as the first principles calculations based on density functional theory to study the valance, concentration, site of incorporation, state of existence, distribution of the acceptor dopant ions in the KNN-based ceramics. The structural defects, defect dipoles, mechanism of charge compensation, chemical driving force of defect structure will also be studied so as to investigate the mechanism of the remarkable effects and to provide experimental evidence for the theoretical work. The comprehensive understanding of the effects of dopants on the microscopic structure as well as the connection to macroscopic electrical properties will be obtained by the comparative study on the similarities and deferences of defect characteristics and electrical properties between perovskite A1+B5+O3-type alkali niobate and A2+B4+O3-type titanate ferroelectrics. In conclusion, this study will promote the research and development of lead-free ceramics and extend the basic research of piezoelectric and ferroelectric materials.

受主掺杂钙钛矿铁电体的缺陷结构/特性及其与宏观电学性质的关联性是铁电压电物理的重要基础研究主题。申请人前期研究发现，Cu改性碱金属铌酸盐KNN具有特异铁电行为、超优硬性压电性质及特殊时效效应，但是产生这些奇特现象的机理尚不清楚。本项目借助电子顺磁共振、正电子湮没技术、PFM/TEM等实验手段并结合第一性原理理论计算，将静态法与动态法结合，重点研究受主改性铌酸盐铁电体中局域缺陷结构、电荷补偿机理、缺陷偶极子形成的化学驱动力、缺陷偶极矩与自发极化的相互作用，阐明KNN基铁电体具有奇特电学性质的微观机制与理论基础；比较研究受主掺杂的钙钛矿铌酸盐和钛酸盐铁电体微观结构及电学行为的异同，揭示并综合理解铁电体中缺陷特性与宏观电学性质的本质联系。研究成果有助于从“材料设计”的角度研发高性能铁电压电材料，深化“缺陷-宏观电学性质”关系的认识，可望丰富铁电压电材料的基础研究内涵，为高技术陶瓷研发提供支撑。

缺陷结构与特性对压电陶瓷的微观结构、介电性、压电性与铁电性等起着至关重要的作用。碱金属铌酸盐陶瓷被认为是最有前景的无铅候选材料之一，但其研究的焦点是如何提高压电常数和机电耦合系数；而对受主离子掺杂的硬性碱金属铌酸盐陶瓷较少涉及。我们的前期研究已经显示出，Cu及含Cu化合物改性的碱金属铌酸盐基陶瓷具有特异铁电行为、超优硬性压电性质及特殊老化效应，但是这些奇特现象所蕴含的机理尚有待深入研究；并且，其它受主离子改性的碱金属铌酸盐陶瓷难以展现出硬性压电行为。基于此，本项目主要开展了下列研究以阐明缺陷结构/特性与Cu改性的碱金属铌酸盐陶瓷的宏观电学性质的关联性：以K0.5Na0.5NbO3+1mol%CuO压电陶瓷为研究对象，系统研究了P-E测试频率/温度、循环、淬火和老化对其缺陷结构/特性和宏观电学性质的影响，阐明了相应的钉扎与退钉扎效应；以Fe2O3、MnO2及CuO掺杂K0.5Na0.5NbO3为研究对象，研究了掺杂离子种类对材料的缺陷结构/特性及宏观电学性质的影响；将含铜化合物KCuTa3O9及CuSb2O6引入K0.5Na0.5NbO3陶瓷，研究了缺陷结构/特性对陶瓷铁电性和压电性的影响；以Cu-Nb及F-O双位取代策略构建了K0.5Na0.5NbO3 + x mol% CuF2无铅压电陶瓷，研究了Cu-Nb及F-O的竞争效应诱导的缺陷特性及宏观电学性能的演化历程；构建了 CuO掺杂的K0.5Na0.5Nb1-xSbxO3无铅压电陶瓷，研究了Sb-Nb取代导致的压电铁电性质的“硬性-软性”演变及其微观缺陷机制；构建了K0.5Na0.5Nb0.996Cu0.01O3−xFx (KNCNF-x)陶瓷，研究了F-O取代对氧空位和缺陷的抑制效应，及其相应的“硬性-软性”演化历程。通过上述系列研究，阐明了Cu及含Cu化合物改性的碱金属铌酸盐基陶瓷具有优异硬性压电性质、奇特铁电行为及特殊老化效应的微观机制，深化了对“铁电体微观结构与宏观电学性质关系”这一铁电物理学重要研究主题的理解。