Lattice dynamics of strong negative thermal expansion materials

非技术摘要：热膨胀是所有材料都具有的性质，并且最常见的是响应于温度升高而体积增加。然而，最近的新材料发现揭示了负热膨胀（NTE）的实例，这是一种特殊的热致体积收缩现象。NTE材料目前未用于工业环境中，但在稳定电信组件方面具有强大的应用潜力，作为受益于热控制应力的电子设备元件，以及形成具有工程热性能的刚性复合结构材料的潜力。该项目使用基于光和X射线的光谱学来研究在一组代表性材料中驱动NTE效应的激发，其目标是实现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进行实验活动，培训下一代高科技劳动力，是该项目的一个组成部分。此外，一个新的课程努力提供初级和高级科学专业的机会，开发适合演示文稿的文件相机平台上的大型演讲霍尔斯，用于在介绍物理类服务的科学和工程新生和大二学生。Doc-cam demos项目的中心主题是在系内教职员工的指导下，为学生和学生提供教育发展。技术摘要：过去10年，人们发现具有强大和相当大的负热膨胀（NTE）的材料的速度加快。我们的目标是推进我们的理解NTE与动力学的紧密结合，刚性的分子单位和本地原子的安排，允许强的核晶格波动的方向横向的结构连接定义的晶胞。由于任何符号的热膨胀必然是一种激发态效应，并涉及非谐相互作用，基本的科学动机围绕着强量子涨落、旋转隧道和多体非线性局域化在这一显着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和热传输测量将在最近发现的NTE材料的一个选定的子集中进行，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。布里渊区边界和区中心模式的详细研究，相信有助于将评估和比较跨材料类。教育活动包括通过一个新项目培训新一代科学家，该项目允许高级科学专业的学生开发新的文档相机演示，供大型讲座使用，从而发挥他们的创造潜力。这门课程的努力在同伴指导和其他最近的科学教学创新的精神翻转演示室。

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.