无铅铁电单晶的压电活性与结构本质

The origin of piezoelectric response is investigated to their hierarchical structure in lead-free ferroelectric single crystals, such as NBT- and KNN-based solid sulution ferroelectrics. The project aims at to design and fabricate new ferroelectric single crystals with high piezoelectric response, low dielectric loss and high temperature stability, and the mechanism how to control the hierarchical structure and optimize their intrinsic and extrinsic piezoelectric performances. The hierarchical structure (lattice distortion→dipole→polar nano regions→nano-domains→macro-domains→phase structure) will be investigated multidimensionally by different techniques such as synchrotron X-ray radiation, transmission electron microscopy (TEM), raman spectrum, piezoelectric force microscope(PFM), polarized light microscopy (PLM) etc. The piezoelectric response will be investigated systematically in chemical composition, order and disorder of solid-solution and external field (such as temperature, strain and electric field) related to their hierarchical structure. Ionic-doping and post-process by atmosphere annealing and poling will be investigatd to optimize the piezoelectric properties of lead-free piezoelectric single crystals. We hope to have better understanding of the mechanism of piezoelectric response to find the fundamental difference between the lead-based MPB and lead-free MPB to design and fabricate novel high performance lead-free piezoelectric materials, and to make the contribution to eliminating lead-based piezoelectric materials eventually in the world.

围绕以钛酸铋钠（NBT）基、铌酸钾钠（KNN）基为代表的钙钛矿型铁电固溶体单晶高压电活性及其结构本质研究，包括高压电性能、低介电损耗、高温度稳定性无铅铁电材料的设计、制备、结构与性能调控机理，开展铁电单晶生长，与单晶材料多层次多尺度结构对本征压电性能和非本征压电性能的影响规律研究；结合同步辐射、透射电镜、拉曼光谱、压力电学显微镜、偏光显微镜等不同手段，研究无铅压电单晶的多层次多尺度（晶格畸变→偶极子→极化团簇→微畴→宏畴→相结构）结构特征与相变规律，揭示无铅压电单晶在外场（温度、电场、应力）作用下压电响应机理与结构本质；以及通过离子掺杂、气氛退火与极化后处理来调控材料多层次结构与压电性能。在此基础上，指导新型高性能无铅压电材料的设计和制备，以及现有无铅压电材料的改性研究，促进尽早实现压电材料无铅化的发展目标。

五年来本重点基金项目，围绕以钛酸铋钠(NBT)基、铌酸钾钠(KNN)基为代表的钙钛矿型铁电固溶体单晶高压电活性及其结构本质进行了研究，开展了铁电单晶生长，与单晶材料多层次多尺度结构对本征压电性能和非本征压电性能的影响规律研究；结合不同实验手段，研究了无铅压电单晶的多层次多尺度结构特征与相变规律，揭示无铅压电单晶在外场(温度、电场、应力)作用下压电响应机理与结构本质。具体研究结果包括，发展了几种无铅铁电单晶生长生长方法，成功生长出了多种大尺寸、高均匀性、高质量的无铅压电单晶NBT-BT、KNN以及NBT-KBT-BT材料，其中NBT-6BT单晶压电常数达到了d33=844 pC/N，d*（εmax/Emax）=1360 pm/V；发现了A位复合钙钛矿型NBT-BT晶格结构特征：（a）从Tm到550 ℃ ，存在着P4bm铁弹相；（b）二种非本征铁电畸变模式的超晶格斑点（P4bm和R3C）共存现象；发现了极性纳米微区（PNRs）沿[001]分布的特征，阐明了八面体顶点相连的NBT-BT晶体存在偏离平均点阵结构的面缺陷；并揭示了Td附近形成双电滞回线的场致诱导相变机制，在Td附近二种不同超晶格斑点数量之间转化所形成介电峰的频率色散机制；揭示了NBT-BT的准同型相界的结构特点，及其在电场激励下的结构变化规律；发现了NBT-BT在准同型相界附近具有超高压电响应与特殊声子的能量交换通道密切联系，（a）存在着二种超晶格斑点（M和R）共存的晶格结构，（b）二种极性纳米微区M和R之间，以及极性纳米微区与晶格格点之间存在着不同的能量交换通道。.本项目已在Advanced Materials, Scripta Materialia, Physcial Review B, Journal of Material Chemistry C等期刊发表SCI收录论文58篇。

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