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

世界许多地方的生态限制要求消除所有消费品中的铅（Pb），这是本研究计划的重要环境背景。这种禁止性的趋势使陶瓷工业处于不稳定的地位，因为它完全依赖于用于压电应用的铅基材料。压电材料广泛应用于传感器、执行器等电子器件中。迄今为止，最受欢迎的材料是基于钙钛矿PbZrxTi 1-xO 3（PZT）的材料，其应用于90%以上的压电市场。目前迫切需要找到PZT的替代品用于压电应用，并且近年来，已经研究了许多材料，例如Na 0.5Bi 0.5TiO 3（NBT）及其与BaTiO 3的固溶体（NBT-BT）或K 0.5Bi 0.5TiO 3（NBT-KBT）、K 0.5Na 0.5NbO 3（KNN）及其与LiTaO 3的固溶体（KNN-LT）作为可能的替代品。较新的无铅材料与PZT结合在一起，因为它们在其相图中显示出晶体结构突然变化的区域，通常从菱面体相到四面体相。该区域被称为准同型相界（MPB），似乎与这些材料的最大压电响应相一致。这是该计划的目的是获得一个统一的科学认识的准同型相界（MPB）区域及其对无铅压电材料的压电性能的影响，作为我们的例子Na0.5Bi0.5TiO3 -BaTiO 3（NBT-BT）固溶体。我们的目标是研究NBT-BT中的MPB，从纳米尺度的科学到宏观的物理性质，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的最全面的描述和理解。为了实现这一目标，目前世界范围内有许多研究致力于对原型MPB系统PZT本身进行完整和适当的描述，其中几个关键问题仍未得到解答。特别是，MPB区域真的是一个新的单斜晶相吗（自从1999年Noheda等人的突破性晶体学研究以来，人们普遍接受了这一点）？或者它是由四面体/菱形对称的自适应纳米畴组成的？还是应该通过相关原子位移驱动的短程有序的增长和减少来解释？这些和更多关于MPB性质的问题必须在无铅MPB系统中得到紧急和直接的回答，以便从根本上理解促进高压电性能的过程，并设计有效的新功能材料。在这个材料全球网络（MWN）计划中，我们将把来自三大洲的领先研究人员结合起来，我们将把为解决MPB纳米科学而开发的新的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。本文的主要目的可以概括为：1.识别纳米畴结构并表征其压电响应; 2.确定结构机制（转换序列），通过该转换序列在非Pb材料中实现高压电性，并识别非Pb和Pb基系统中MPB之间的相似性和差异; 3利用这种理解来提高NBT-BT和非铅系统的压电性能。4通过英国/每个组织要求的资源总额：沃里克489，758（EPSRC捐款403，174）：牛津65，183（EPSRC捐款52，147）联合王国资源总额：554，941（EPSRC捐款455，321）

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)