NSF: Materials World Network: Nanoscale Structure-Property Relationships in Lead Free Morphotropic Phase Boundary Piezoelectrics

世界上许多地方的生态限制要求从所有消费品中消除铅，这是本研究计划的一个重要环境背景。这种令人望而却步的趋势使陶瓷工业处于不稳定的地位，因为它完全依赖铅基材料用于压电应用。压电材料广泛应用于传感器、执行器和其他电子器件中。迄今为止，最受欢迎的材料是基于钙钛矿PbZrxTi1-xO3 （PZT）的材料，在超过90%的压电市场中使用。在压电应用中，迫切需要寻找PZT的替代品，近年来，许多材料如Na0.5Bi0.5TiO3 （NBT）及其与BaTiO3的固溶体（NBT- bt）或K0.5Bi0.5TiO3 (NBT- kbt), K0.5Na0.5NbO3 （KNN）及其与LiTaO3的固溶体（KNN- lt）被研究作为可能的替代品。较新的无铅材料与PZT的统一之处在于，它们在相图中表现出晶体结构突然变化的区域，通常从菱形相转变为四边形相。这一区域被称为嗜形相边界（MPB），似乎与这些材料的最大压电响应一致。本项目以Na0.5Bi0.5TiO3 - BaTiO3 （NBT-BT）固溶体为例，旨在对无铅压电材料中嗜形相边界（MPB）区域及其对压电性能的影响有一个统一的科学认识。我们的目标是从纳米尺度的科学到宏观物理性质来研究NBT-BT中的MPB，从而探索这种材料作为功能无铅替代品的全部潜力，并提供迄今为止无铅系统中MPB最彻底的描述和理解。为了将这一目标置于上下文中，目前世界范围内有许多研究解决了原型MPB系统PZT本身的完整和适当描述，其中几个关键问题仍未得到解答。特别是，MPB区域是否真的是一个新的单斜晶相（自1999年Noheda等人的晶体学研究取得突破性进展以来，人们普遍接受了这一点）？还是由自适应的四边形/菱形对称纳米结构域组成？还是应该通过相关原子位移驱动的短程序的增长和减少来解释？这些以及关于MPB性质的进一步问题必须在无铅MPB系统本身中得到迫切和直接的回答，这既是为了对促进高压电性能的过程的基本理解，也是为了设计有效的新功能材料。在这个材料全球网络（MWN）项目中，我们将结合来自三大洲的领先研究人员，将已经开发出来的用于解决MPB纳米科学的新先进实验方法应用于无铅材料NBT/BT，这是本提案的最终目标。主要目的可以概括为：1 .确定纳米级畴结构并表征其压电响应；2 .确定在非pb材料中实现高压电性的结构机制（转换序列），并确定非pb和pb基体系中MPBs的异同；利用这一认识来改善NBT-BT和非pb体系的压电性能通过英美合作和交流，为博士和早期职业科学家提供更好的研究教育和经验。每个组织的总资源请求：华威大学489,758 (EPSRC贡献403,174)：牛津大学65,183 （EPSRC贡献52,147）英国总资源：554,941 （455,321 EPSRC贡献）

Ecological restrictions in many parts of the world are demanding the elimination of lead (Pb) from all consumer items, an important environmental context that underlies this research programme. This prohibitive trend places the ceramics industry in a precarious position as it is entirely dependent on Pb-based materials for piezoelectric applications. Piezoelectric materials are widely used in sensors, actuators and other electronic devices. The most popular materials to date are those based on the perovskite PbZrxTi1-xO3 (PZT), in use in over 90% of the piezoelectricity market. There is an urgent need to find alternatives to PZT for piezoelectric applications and in recent years, a number of materials such as Na0.5Bi0.5TiO3 (NBT) and its solid-solutions with BaTiO3 (NBT-BT) or K0.5Bi0.5TiO3 (NBT-KBT), K0.5Na0.5NbO3 (KNN) and its solid solution with LiTaO3 (KNN-LT) have been researched as possible replacements. The newer lead-free materials are united with PZT in that they exhibit a region in their phase diagrams where there appears to be a sudden change in crystal structure, typically from a rhombohedral to a tetragonal phase. This region has been termed the Morphotropic Phase Boundary (MPB) and appears to coincide with the maximum piezo-response of these materials. It is the aim of this programme to obtain a unified scientific understanding of the morphotropic phase boundary (MPB) region and its impact upon piezoelectric properties in lead-free piezoelectric materials, taking as our example the Na0.5Bi0.5TiO3 - BaTiO3 (NBT-BT) solid solution. We aim to investigate the MPB in NBT-BT from the nano-scale science to the macroscopic physical properties thus exploring this material's full potential as a functioning lead-free alternative and providing the most thorough description and understanding of an MPB in a lead-free system to date. To put this aim in context, there is currently much research world-wide addressing the full and proper description of the archetypal MPB system PZT itself, for which several key questions remain unanswered. In particular, is the MPB region truly a new monoclinic crystalline phase (as has generally accepted since the breakthrough crystallographic studies of of Noheda et al in 1999)? Or does it consist of adaptive nano-domains of tetragonal/rhombohedral symmetry? Or should it be explained through the growth and diminution of short-range order driven by correlated atomic displacements? These and further questions about the nature of the MPB must be answered URGENTLY and DIRECTLY in lead-free MPB systems themselves both for a fundamental understanding of the processes that promote high piezoelectric properties and to engineer effective new functional materials. In this materials-worldwide-network (MWN) programme, which combines leading researchers from three continents, we will apply the new and advanced experimental methodologies that have been developed to address the nano-science of the MPB to the lead-free material, NBT/BT, which is the ultimate goal of this proposal. The principal aims can be summarised as:1 To identify the nanoscale domain structure and characterize its piezoelectric response; 2 To determine the structural mechanism (transformational sequences) by which high piezoelectricity is achieved in non-Pb materials, and identify similarities and differences between MPBs in non-Pb and Pb-based systems; 3 To use this understanding to improve piezoelectric properties in NBT-BT and non-Pb systems.4 To provide an enhanced research education/experience for PhD and early-career scientists via UK/US collaborations and exchanges.Total Resource Request by each Organisation: Warwick 489,758 (EPSRC contribution 403,174): Oxford 65,183 (EPSRC contribution 52,147)Total UK resources: 554,941 (455,321 EPSRC contribution)