权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Analysis of Polar Nanostructures in High Temperature Relaxor Dielectrics: a Framework for Materials Discovery

高温弛豫电介质中极性纳米结构的分析：材料发现的框架

基本信息

批准号：
EP/P015514/1
负责人：
Steven Milne
金额：
$ 59.18万
依托单位：
University of Leeds
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FP015514%2F1
关键词：
Analysis Polar Nanostructures Temperature Relaxor

项目摘要

Existing commercial high temperature, high charge storage dielectrics fail to operate successfully above 200 C - but for emerging power and harsh environment electronics which are important in renewable energy, aerospace and automotive industries, capacitor materials are required with stable, robust dielectric performance to temperatures of 300 C and higher. Against this background, we propose a fundamental study of local crystal structure to discover the scientific principles behind a non-conventional type of polar oxide ceramic which could offer a breakthrough in high temperature capacitor technology. The materials are derived from relaxor ferroelectrics, so called because of a wide frequency relaxation in their dielectric properties. The motivation is to permit the UK capacitor manufacturing industry to create new products and to bring about advances in power and harsh environment electronics. Relaxor ferroelectrics, such as those based on lead magnesium niobate, differ from normal ferroelectrics as they exhibit polar order over length scales of only a few nanometers (as opposed to microns in a normal ferroelectric). A strong peak in the relative permittivity-temperature response is due to the interplay of increased polar length scales and changes to the dynamics of polar coupling on cooling. Conventional relaxors show a large temperature dependence, making them unsuitable for use in capacitors. By empirical compositional engineering, it has been shown that the relative permittivity peak can be supressed and temperature-stable charge storage induced over wide temperature ranges, with ceiling temperatures > 300 C. These new temperature-stable, high temperature relaxors show promise for creating next-generation high-temperature capacitors but existing materials fail to meet industry needs: (a) stable relative permittivity does not extend to industry standard lower temperatures of -55 C; (b) relative permittivity is less than 50% of commercial sub-200 C capacitors; (c) dielectric losses are too high, especially at the extremes of temperature. A lack of any scientific understanding of how the polar nanostructure of a relaxor ferroelectric is changed by increasing levels of crystal lattice substitution to create temperature stable performance is the major obstacle to device-standard breakthroughs. We will remove this barrier, and so facilitate the design of innovative high-temperature dielectrics by discovering the nanostructural and nanochemical factors responsible for converting a normal to a temperature-stable relaxor. Currently, no one knows why certain chemical modifications flatten the dielectric response. We shall reveal the underpinning scientific principles by studying one of the best existing temperature-stable relaxor solid solution systems: Ca modified BaTiO3-Bi(Mg0.5Ti0.5)O3. This changes from a ferroelectric to a conventional relaxor ferroelectric to a temperature-stable relaxor with increasing levels of substitution of Bi and Mg for Ba/Ca and Ti in the formulation. Structures will be studied using advanced nanoscale analysis techniques: atomic image resolution scanning electron microscopy for direct imaging of nanostructure over 10's-100's of nm; shorter range analysis to yield details of average local co-ordination environments, bond lengths and electronic structure using X-ray absorption techniques; and with atomistic computer modelling to support data interpretation. In conjunction with electrical property measurements, this multi-disciplinary approach will elucidate structure-performance criteria. The aim is to apply the new knowledge to design high temperature dielectric materials specified from -55 to 300 C that will revolutionise high-temperature capacitor technology, bringing economic and environmental benefits to the UK.

现有的商用高温、高电荷存储电容器无法在200 ℃以上成功运行，但对于新兴的电力和恶劣环境电子产品（在可再生能源、航空航天和汽车工业中非常重要），电容器材料需要在300 ℃及更高温度下具有稳定、稳健的介电性能。在此背景下，我们提出了一个本地晶体结构的基础研究，以发现背后的非传统类型的极性氧化物陶瓷，可以提供一个突破高温电容器技术的科学原理。这些材料来自弛豫铁电体，之所以这样称呼是因为它们的介电性质具有宽频率弛豫。其动机是允许英国电容器制造业创造新产品，并带来电力和恶劣环境电子产品的进步。弛豫铁电体，例如基于铅镁铁电体的那些，与正常铁电体不同，因为它们在仅几纳米的长度尺度上表现出极序（与正常铁电体中的微米相反）。一个强大的峰值，在相对磁导率的温度响应是由于增加的极性长度尺度和变化的相互作用的动力学极性耦合冷却。传统的弛豫器显示出很大的温度依赖性，使得它们不适合用于电容器。通过经验组成工程，已经表明，相对介电常数峰值可以被抑制，并且在宽的温度范围内诱导温度稳定的电荷存储，其中上限温度> 300 ℃。这些新的温度稳定的高温弛豫剂显示出用于制造下一代高温电容器的前景，但是现有材料不能满足工业需要：（a）稳定的相对介电常数不能扩展到工业标准的-55 ℃的较低温度;（B）相对介电常数小于商业低于200 ℃的电容器的50%;（c）介电损耗太高，特别是在极端温度下。缺乏对弛豫铁电体的极性纳米结构如何通过增加晶格取代水平来改变以创造温度稳定性能的任何科学理解是器件标准突破的主要障碍。我们将消除这一障碍，并通过发现负责将正常转换为温度稳定的弛豫子的纳米结构和纳米化学因素，从而促进创新的高温弛豫子的设计。目前，没有人知道为什么某些化学修饰会使介电响应变平。我们将通过研究现有最好的温度稳定的弛豫固溶体系统之一：Ca改性的BaTiO 3-Bi（Mg 0.5Ti 0.5）O3来揭示其基础科学原理。随着配方中Bi和Mg对Ba/Ca和Ti的取代水平的增加，这从铁电体变为常规弛豫铁电体，再变为温度稳定的弛豫体。将使用先进的纳米级分析技术研究结构：原子图像分辨率扫描电子显微镜，用于直接成像超过10 -100纳米的纳米结构;使用X射线吸收技术进行短程分析，以获得平均局部配位环境，键长和电子结构的细节;以及原子计算机建模，以支持数据解释。结合电性能测量，这种多学科的方法将阐明结构性能标准。其目的是将新知识应用于设计-55至300 C的高温介电材料，这将彻底改变高温电容器技术，为英国带来经济和环境效益。