钨青铜结构碱土碱金属铌酸盐铁电陶瓷的A位离子设计、结构分析和电性能研究

Tungsten bronze alkaline earth-alkali metal niobates are considered as key functional materials with broad application prospects owing to their superior dielectric, ferroelectric, piezoelectric, pyroelectric and electro-optic properties. However, the compositional diversity and structural complexity make its performance difficult to control, which limits its application. In this project, we intend to prepare densitified (Ca,Sr,Ba)2(Li,Na,K)xNb5O15 ceramics using two-step sintering process. The relation among A-site-cation design, crystal structure and electrical properties are studied systematically. The accurate microstructure information (such as cell parameters, crystal space group, atomic coordinates, bond lengths and angles) is obtained by using the high-resolution XRD measurement and Rietveld refinement method. By exploring the relation between microstructure factors and electrical properties, the intrinsic structure causes of electrical properties will be revealed. In terms of mesoscopic structure, the morphotropic phase boundary can be determined through analyzing the phase structure transition with composition and temperature. Effects of phase structure evolution behavior, ferroelectric domain structure and domain shifts on the electrical properties are studied in detail to clarify the corresponding mechanisms for high performance. It can be expected to obtain the ion-selective principle for high-performance and regulate the electrical properties from the perspective of structural design and analysis in this project. This study will not only provide theoretical basis on regulation of performance for tungsten bronze niobates, but also provide new high-performance materials for lead-free piezo-ferroelectric devices.

钨青铜结构碱土碱金属铌酸盐具有奇特的介电、铁电、压电、热释电和光电效应等，是一类具有广阔应用前景的关键功能材料。然而其组成多变性和晶体结构复杂性使性能难以调控，限制了其应用。本项目选择(Ca,Sr,Ba)2(Li,Na,K)xNb5O15作为材料基元，通过调节A位碱土、碱金属离子进行组成设计，采用二步烧结技术制备致密陶瓷。通过高分辨率XRD等表征手段结合Rietveld晶体结构精修方法，获取晶胞参数、晶体空间群、原子坐标、键长和键角等重要的微观结构信息，探讨微观结构因素与电性能的关联性，揭示电性能的结构根源；通过晶相结构分析确定准同型相界MPB，阐明晶相结构演变行为、电畴结构和畴转变等介观结构因素对陶瓷宏观电性能的影响机制，获取与高性能相关的离子选择原则，以期从结构设计和分析的角度实现电性能的调控。本项目不仅为钨青铜结构材料的性能调控提供理论依据，而且为无铅压铁电器件开发提供高性能新材料。

针对钨青铜结构铁电体具有灵活多变的晶体结构优势和丰富的物理性能特征， 本项目主要从研究四方钨青铜结构陶瓷(TTB)“组成-结构-性能”之间的关联性角度出发，分别以钨青铜结构碱土-碱金属铌酸盐铁电陶瓷Ca0.28Ba0.72Nb2O6 (CBN28)、Sr0.53Ba0.47Nb2O6 (SBN53)和Sr0.85Ca0.15Nb2O6 (SCN85)材料体系作为研究对象，通过不同种类和含量的碱土、碱金属离子进行A位组成设计，研究A位离子取代和空穴位置的占据情况对陶瓷相结构、显微形貌、介电及铁电性能的影响，着重阐明了结构因素与电性能之间的关联性。首先，采用传统固相法，结合二步烧结过程，通过调整工艺参数获得了不同体系的致密陶瓷样品。其次，系统研究了A位离子取代对样品相结构、微观晶胞参数、Nb-O八面体畸变程度和晶粒各向异性生长行为等显微结构的影响规律。并进一步结合组成变化对介电和铁电性能的影响情况，在获得电性能较为优越的材料体系的同时，探索研究了电性能的结构机制。.①通过对Ca0.28Ba0.72Nb2O6 (CBN28)体系进行三种不同A位离子取代的组成设计，研究了组成-结构-性能之间的关联性，获得了Na取代最有利于提高Nb-O八面体畸变程度、促进陶瓷致密化和相结构的稳定性、从而优化电性能的重要结果。.②通过对Sr0.53Ba0.47Nb2O6 (SBN53)体系进行A位Na取代的含量变化研究，设计其结构从钨青铜未充满型到充满型，并进一步到完全充满型的转变，获得了充满型结构中其A-NbO6 振动模式最强，Nb-O八面体的畸变程度最大且介电和铁电性能最为优越的重要结果。.③通过对Sr0.85Ca0.15Nb2O6 (SCN85)体系进行A位Na取代以及Sr/Ca比含量变化的组成设计，研究了组成-结构-性能之间的关联性，在探讨组成设计对结构和性能变化影响规律的同时，进一步获得了在钨青铜结构碱土碱金属铌酸盐材料体系中电性能最为突出的材料体系：(Sr0.925Ca0.075)2.1Na0.8Nb5O15因其在室温附近存在铁电-铁弹相变从而表现出优越的压铁电性能。. 以上结果可为碱金属铌酸盐钨青铜结构材料电性能调控提供重要的理论依据，而且其获得的高性能材料体系也具有一定的应用前景。本项目无论从执行过程，成果产出，还是从人才培养来看，项目组都顺利完成了预定计划。