Lattice dynamics of strong negative thermal expansion materials

强负热膨胀材料的晶格动力学

• 批准号: 1506825
• 负责人: Jason Hancock
• 金额: $ 38.2万
• 依托单位: University of Connecticut
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-05-01 至 2018-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1506825&HistoricalAwards=false
• 关键词: Lattice; dynamics; strong; negative; thermal

Non-technical abstract: Thermal expansion is a property that all materials possess and most commonly occurs as a volume increase in response to a temperature increase. However, recent new materials discoveries have revealed instances of negative thermal expansion (NTE), a peculiar phenomenon of heat-induced volume contraction. NTE materials are not currently used in industrial contexts, but hold strong application potential in stabilizing telecommunication components, as elements of electronic devices benefiting from thermally controlled stresses, and the potential to form rigid composite structural materials with engineered thermal properties. This project uses light- and X-ray-based spectroscopy to study excitations driving the NTE effect in a representative set of materials with the goal of achieving an understanding capable of leading new material discovery efforts. Training of the next generation's high-tech workforce through both graduate and undergraduate participants performing experimental activities at Connecticut's flagship state university and national user facilities is an integrated component of the project. In addition, a novel curricular effort offers junior and senior science majors the opportunity to develop demonstrations suitable for presentation on a document camera platform in large lecture halls for use in introductory physics classes serving science and engineering freshmen and sophomore students. Educational development for students and by students, guided by departmental faculty and staff, is a central theme of the Doc-cam demos project.Technical abstract: The past 10 years has seen an accelerated rate of discovery of materials with robust and sizable negative thermal expansion (NTE). The goal is to advance our understanding of NTE associated with dynamics of tightly bound, stiff molecular units and local atomic arrangements allowing for strong nuclear lattice fluctuations in a direction transverse to a structural linkage defining the unit cell. Because thermal expansion of any sign is necessarily an excited state effect and involves anharmonic interactions, the basic science motivation surrounds the likely possibilities that strong quantum fluctuations, rotational tunneling, and many-body nonlinear localization play a role in this remarkable effect. Inelastic X-ray scattering, infrared and terahertz absorption spectroscopy, and thermal transport measurements will be performed in a select subset of recently discovered NTE materials whose structures have related features, including members possessing the important perovskite structure. Detailed study of Brillouin zone boundary and zone-center modes believed to contribute will be assessed and compared across materials classes. Educational activities involve training a new generation of scientists through a novel project permitting advanced science majors to exercise their creative potential by developing new document camera demonstrations for use in large lecture settings. This curricular effort flips the demo room in the spirit of peer instruction and other recent science teaching innovations.

非技术摘要：热膨胀是所有材料都具有的特性，最常见的情况是随着温度的升高而增大体积。然而，最近新材料的发现揭示了负热膨胀(NTE)的例子，这是一种由热引起的体积收缩的特殊现象。NTE材料目前没有用于工业领域，但作为受益于热控制应力的电子设备的元件，在稳定电信部件方面具有很强的应用潜力，并有可能形成具有工程热性能的刚性复合材料结构材料。该项目使用基于光和X射线的光谱学来研究在一组有代表性的材料中驱动NTE效应的激发，目的是实现对能够领导新材料发现工作的理解。通过研究生和本科生参与者在康涅狄格州的旗舰州立大学和国家用户设施开展实验活动，培训下一代高科技劳动力是该项目的一个组成部分。此外，一项新颖的课程努力为理科专业的低年级和高年级学生提供了一个机会，让他们有机会开发适合在大型报告厅的文件摄像机平台上演示的演示，用于为理工科一年级和二年级学生服务的入门物理课程。在系教职员工的指导下，学生和学生的教育发展是Doc-Cam演示项目的中心主题。技术摘要：在过去的10年里，发现具有强大和相当大的负热膨胀(NTE)的材料的速度加快了。我们的目标是促进我们对NTE的理解，这些NTE与紧密结合的、僵硬的分子单元和局部原子排列的动力学有关，允许在横向于定义单元单元的结构连接的方向上发生强烈的核晶格波动。由于任何符号的热膨胀必然是一种激发态效应，并涉及非简谐相互作用，所以基本的科学动机围绕着强烈的量子涨落、旋转隧道和多体非线性局域在这种显著效应中发挥作用的可能性。非弹性X射线散射、红外和太赫兹吸收光谱以及热输运测量将在最近发现的NTE材料的精选子集中进行，这些材料的结构具有相关特征，包括具有重要钙钛矿结构的成员。对布里渊区域边界和区域中心模式的详细研究被认为是贡献的，将在材料类别中进行评估和比较。教育活动包括通过一个新颖的项目培训新一代的科学家，该项目允许高级科学专业的学生通过开发用于大型讲座环境的新文件相机演示来发挥他们的创造潜力。这项课程的努力在同行指导和其他最近的科学教学创新的精神下颠覆了演示室。