片状KNN模板晶粒的可控制备、形成机理及织构化陶瓷研究

Potassium sodium niobate (KNN) lead-free piezoceramics have been attracted much attention in recent years. The template crystal growth texturing technology is the most effective way to improve the piezoelectric properties and temperature stability of the KNN ceramics. The existing heterogeneous template crystals have become drawback of the piezoelectric properties improvement of textured KNN-based ceramics. Therefore, the preparation of homogeneous KNN template crystal with plate-like structure is the key technology for the fabrication of high performance textured KNN-based piezoceramics. This project will adopt two kinds of method, namely direct molten salt method for one-step synthesis and proton substitution multi-step reaction method, to prepare the plate-like KNN powder. The related forming mechanism is studied by means of modern testing and analysis, trying to find out the scientific method to overcome the cubic growth habit for KNN crystal. Using plate-like KNN template crystal as homogeneous templates, the slurry with high solid content and good stability is prepared through optimizing dispersing agent and binder. Tape-casting method is used to prepare textured KNN-based lead-free piezoceramics. Based on the study of interrelationship among tape-casting technology, microstructure and electrical properties, the textured KNN-based lead-free piezoceramics with high performance and good temperature stability are optimally prepared. This study will enrich the theory system of textured KNN-based piezoceramics research, and expand their value in practical applications.

铌酸钾钠(KNN)是近年来无铅压电陶瓷材料的研究热点。模板晶粒生长织构化技术是提高KNN陶瓷压电性能及其温度稳定性最有效的方法，现有的异质模板晶粒已经成为制约织构化KNN基陶瓷压电性能提高的瓶颈。因此，制备出具有片状结构的KNN同质模板晶粒是制备高性能织构化KNN基压电陶瓷的关键技术。本项目拟采用直接熔盐法一步合成和质子取代多步反应法两种方法实现片状KNN晶粒的制备，采用现代测试分析手段研究其形成机理，寻找出克服KNN晶粒立方块状结构生长习性的科学方法。以此片状KNN晶粒为同质模板，优选分散剂和粘结剂，制备出固相含量高且稳定均匀分散的流延浆料。采用流延成型技术制备织构化KNN基无铅压电陶瓷，研究流延成型工艺、微观结构、电学性能之间的相互关联性，优化制备出高性能且温度稳定性好的织构化KNN基无铅压电陶瓷。本研究可望丰富织构化KNN基压电陶瓷研究的理论体系，拓展KNN基无铅压电陶瓷的应用价值。

铌酸钾钠（KNN）无铅压电陶瓷因其环境友好而得到广泛研究，为了提高其压电性能，采用（反应）模板晶粒生长技术制备织构化压电陶瓷是提高性能的重要技术，合适的模板晶粒则是制备织构化压电陶瓷的关键。本项目围绕片状KNN和Nb2O5模板晶粒的制备及相关机理、织构化制备技术、高性能KNN基无铅压电陶瓷等展开科学研究，主要研究内容和成果如下：.(1) 片状KNN和Nb2O5模板晶粒的制备及其形成机理的研究。以分析纯的K2CO3和Nb2O5为原料，加入一定量的KCl作为熔盐，合成出片状前驱物K4Nb6O17 (K4N6)颗粒。首先将片状K4N6和K2CO3 混合，以KCl和NaCl为混合熔盐，熔盐法可将K4N6完全转换为KNN片状粉体。其次是将片状K4N6粉体置于6 M 的质子取代剂(HCl)溶液中反应，可获得厚度为1～4μm、长度30～50μm的Nb2O5片状粉体。 .（2）织构化KNN基无铅压电陶瓷的制备及机理的研究。首先以片状Nb2O5为模板晶粒，在固相法合成的KNN 基体粉体中加入15 wt%的Nb2O5模板晶粒与分散剂三乙醇胺，粘结剂苯丙乳液、塑性剂丙三醇以及成膜助剂磷酸三正丁酯混合制备出可流延的浆料，经过流延、干燥、切片、叠片、热压成型、排胶后在一定的温度下烧结，得到织构度0.78织构化KNN陶瓷，其压电性能平行方向d33=141pC /N，kp=39.7%，垂直方向d33=112pC /N，kp=37.5%。此外，采用KNN为基料粉体和片状KNN为模板晶粒，制备出粉体固含量55wt%（其中模板剂15%），溶剂水20.5wt%，分散剂PVP 5.5wt%，粘结剂苯丙乳液13.5wt%，增塑剂丙三醇5.5wt%的水系流延浆料，流延后的膜片表面光滑、均匀、塑性好。.其次以片状KNN为模板晶粒，以掺杂改性后的KNNLST-BZ为基料粉体，流延获得的织构化压电陶瓷具有以下性能d33=248pC/N，k31=32.54%。 . (3) 高性能KNN基无铅压电陶瓷的掺杂改性研究。分别研究了A位离子如Li+和B位离子如Ta3+、Sb3+等对KNN的掺杂改性，或通过添加第二组元，研究获得准同型相界或多型相界组成，大幅度提高压电性能。其中研究获得性能最好的组成是：KNNLST-BZ组成的d33=372 pC/N， kp=47.2%，tanδ=3.1%，ε T 33 /ε0=1470。