Quenching enhanced lattice polarizability in lead-free ferroelectrics

压电材料约占世界电瓷市场的25%，由于其小型化的潜力，预计将进一步增长。虽然大多数这些应用使用钙钛矿Pb（Zr，Ti）O3（PZT），但由于对毒性和环境破坏的担忧不断升级，正在采取措施用无铅替代品取代它。在过去的二十年里，对无铅铁电体的广泛研究已经达成了一个普遍的共识，即没有任何一类无铅材料可以取代用途广泛的PZT。在逐步淘汰铅基铁电体的过程中，无铅材料有望取代PZT，首先是在要求相对较低的严格要求的高功率超声应用中。在几种无铅材料中，铋（Bi）基材料具有显著的优势。与PZT相比，（1-x）Na 1/2Bi 1/2 TiO 3-xBaTiO 3（NBT-BT）组合物是有益的，因为它们具有特别好的高功率特性。BiFeO 3（BF）具有与Pb 2+类似的孤对效应，是另一种有望取代PZT用于高温应用的材料。 然而，这些材料必须进行微调，以适应特定条件下的设备operation.It最近被证明，淬火提高Bi基铁电体的热稳定性和铁电性能。在本项目中，将研究淬火Bi基材料的作用，以（a）优化淬火条件以避免微裂纹并获得所需的材料性能，（B）了解增强的晶格畸变的结构起源，这归因于增加的热稳定性和改善的铁电性能，以及（c）确立淬火作为定制功能材料的材料性质的替代加工路线。这将通过研究代表性的弛豫NBT-BT和铁电BF-BT组合物来实现。该提案中讨论的初步工作为优化淬火条件提供了基础，结合电气和机械性能测量将建立加工路线。平均（同步辐射衍射）和本地（对分布函数分析和透射电子显微镜）的结构分析将探测阳离子排序，Bi 3+偏心和淬火引起的相移的细节。在弛豫体的特定情况下，淬火诱导的铁电秩序将从极性纳米区域的详细表征和定量研究。从这项研究中建立的全面的结构-微观结构-加工-性能相关性有望促进淬火作为一种通用工具来定制功能材料的性能。

Piezoelectric materials constitute about 25% of the world’s market of electroceramics and is expected to grow further due to their potential for miniaturization. While majority of these applications employ the perovskite Pb(Zr,Ti)O3 (PZT), steps are being taken to replace it with lead-free alternatives due to escalating concerns of toxicity and environmental damage. Extensive research on lead-free ferroelectrics in the past two decades has resulted in a general consensus that, there is no single class of lead-free material that can replace the versatile PZT. In the phasing out of lead-based ferroelectrics, the lead-free materials are foreseen to replace PZT, firstly in high power ultrasonic applications that demand relatively lower stringent requirements. Of the several lead-free classes of materials, bismuth (Bi) based materials offer significant advantages. The (1-x)Na1/2Bi1/2TiO3-xBaTiO3 (NBT-BT) compositions are beneficial due to their exceptionally good high power characteristics, in comparison to PZT. BiFeO3 (BF) with Bi3+ exhibiting lone-pair effect similar to Pb2+, is another promising material foreseen to replace PZT for high temperature applications, in future. Yet, these materials have to be fine-tuned to suit specific conditions under device operation.It was recently demonstrated that quenching enhances the thermal stability and ferroelectric properties of Bi based ferroelectrics. In this project, the role of quenching Bi-based materials will be investigated to (a) optimize the quenching conditions to evade microcracking and obtain desired material properties, (b) understand the structural origin of the enhanced lattice distortion, which is attributed to the increased thermal stability and improved ferroelectric properties and (c) establish quenching as an alternate processing route to tailor material properties of functional materials. This will be achieved by studying the representative relaxor NBT-BT and ferroelectric BF-BT compositions. The preliminary work discussed in the proposal provides the basis for optimizing the quenching conditions, which combined with electrical and mechanical property measurements will establish the processing routes. The average (synchrotron diffraction) and local (pair-distribution function analysis and transmission electron microscopy) structural analysis will probe the details of cation ordering, Bi3+ off-centering and quenching induced phase shifts. In the specific case of relaxors, quenching induced ferroelectric order will be investigated from the detailed characterization and quantification of polar nano regions. The comprehensive structure-microstructure-processing-property correlation established from this study is expected to promote quenching as a generic tool to tailor properties of functional materials.