Mechanisms of Ferroelasticity and Ferroelastic Transformations in Ceramics

陶瓷中的铁弹性和铁弹性转变机制

• 批准号: 9972114
• 负责人: Waltraud Kriven
• 金额: $ 31.5万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-07-15 至 2003-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9972114&HistoricalAwards=false
• 关键词: Mechanisms; Ferroelasticity; Ferroelastic; Transformations; Ceramics

9972114KrivenThe objective of this project is to investigate mechanisms of ferroelasticity in ceramics in the context of ferroelastic phase transformations producing domains and their mutual arrangements in resulting microstructures. The current generation of actuators are based on inducing a mechanical response in ferroelectric materials by a variety of electrical, pyro-, piezo- or optical stimuli. These stimuli initiate phase transformations in structures that are usually orthorhombic perovskites. Normally the accompanying volume and/or unit cell shape changes are extremely small (much less than 1%) so that the strains delivered for actuation are of the order of 10E-4. This small strain is usually of little concern and often beneficial in sensor-actuator systems that are cycled extremely rapidly. However, there are applications where there is a need for actuators that are capable of delivering large mechanical forces, both at ambient and at high temperatures. One approach to achieving this goal is through the phenomena of ferroelasticity and ferroelastic transformations. An understanding of the domain rearrangement mechanisms and their limitations will enable us to address the feasibility of mechanical poling of ferroelastic domains in non-perovskites, so as to produce textured or crystallographically aligned thick films of large force-generating actuator materials. The use of non--perovskite crystal structures that are accompanied by significant volume and unit cell shape changes is the key to the large forces generated. In this project, single crystals as well as polycrystalline specimens will be prepared and examined. The crystal structures, lattice parameters and thermal expansion coefficients of phases in a ferroelastic transformation sequence will be determined. Where possible, the high temperature crystal structures will be analyzed in situ, in air, at temperatures up to 2,000 deg C, using X-ray diffraction and synchrotron radiation, with some collaborative neutron diffraction studies. Once armed with the basic crystallographic data, the investigation will be quantitative in studying mechanisms of ferroelastic domain rearrangements and deformation twinning as seen by a range of electron microscopy techniques (TEM, CBED, HREM and SEM, EBSP). The experimental observations will be compared with the theoretical mechanisms proposed in the literature and by the PI. In choosing materials, primarily oxides materials are considered because of their prolific phase transformations, that are presumably due to the mixed ionic-covalent type bonding comprising their crystal structures. Initially some known or suspected ferroelastic transformations will be examined as model systems to understand the phenomena of ferroelasticity and ferroelastic transformations. Later the search will be expanded to the forefront of knowledge in this field, and a choice will be made from known displacive transformations that have potential technological applicability. %%%A comprehensive investigation of ferroelasticity and ferroelastic transformation mechanisms, using a variety of complementary techniques is planned. This promising approach may lead to large force, ambient and high temperature actuation for use in advanced technological applications. The PI will be collaborating with researchers at various national laboratories and at other US and international institutions in this project that will also involve undergraduate students.***

9972114 kriven这个项目的目的是在铁弹性相变的背景下研究陶瓷中的铁弹性机制，产生畴和它们在由此产生的微观结构中的相互排列。当前一代的致动器是基于通过各种电、热、压电或光学刺激在铁电材料中诱导机械响应。这些刺激在通常为正交钙钛矿的结构中引发相变。通常伴随的体积和/或单元胞形状变化非常小（远小于1%），因此用于驱动的应变为10E-4量级。这种小的应变通常是很少关注的，并且在循环极快的传感器-执行器系统中通常是有益的。然而，有些应用需要能够在环境和高温下提供大机械力的执行器。实现这一目标的一种方法是通过铁弹性和铁弹性变换现象。对畴重排机制及其局限性的理解将使我们能够解决非钙钛矿中铁弹性畴机械极化的可行性，从而产生有织构或晶体排列的大型力致动器材料厚膜。非钙钛矿晶体结构的使用伴随着显著的体积和单元胞形状变化，这是产生巨大力的关键。在这个项目中，将制备和检测单晶和多晶样品。确定铁弹性相变序列中相的晶体结构、晶格参数和热膨胀系数。在可能的情况下，高温晶体结构将在空气中，在高达2000摄氏度的温度下进行原位分析，使用x射线衍射和同步辐射，以及一些协同中子衍射研究。一旦有了基本的晶体学数据，研究将定量研究铁弹性畴重排和变形孪晶的机制，通过一系列电子显微镜技术（TEM， CBED， HREM和SEM， EBSP）。实验观测结果将与文献和PI提出的理论机制进行比较。在选择材料时，主要考虑氧化物材料，因为它们具有丰富的相变，这可能是由于混合离子-共价键构成了它们的晶体结构。最初，一些已知或怀疑的铁弹性变换将作为模型系统来研究，以理解铁弹性和铁弹性变换的现象。随后，搜索将扩展到该领域知识的前沿，并将从已知的具有潜在技术适用性的替代转换中做出选择。计划使用各种互补技术对铁弹性和铁弹性转换机制进行全面研究。这种有前途的方法可能会导致大力，环境和高温驱动，用于先进的技术应用。该项目将与多个国家实验室以及其他美国和国际机构的研究人员合作，本科生也将参与其中