The Influence of Nanostructure and Pressure on the Properties of Low and Negative Thermal Expansion Materials

热膨胀在确定材料是否适用于特定应用方面起着非常重要的作用。拟议的工作将导致在低和负的热膨胀（NTE）材料的结构性能关系，以及控制热膨胀的策略的增强理解。在各种低和负TE材料的热膨胀（TE）的压力依赖性将被检查，以建立的因素，导致高度压力依赖性的热膨胀系数（CTE）在这样的材料。据推测，在NTE材料中的低压相变将导致相当广泛的极压敏感性的发生。CTE的压力依赖性是NTE填料可能经受应力的复合材料的设计考虑因素。热膨胀的控制，通过修改的O：F的比例，在氟氧化物与ReO 3框架结构，将被检查和基本的结构性质的关系，通过分别询问M-F-M和M-O-M链接的温度和压力的响应，使用总散射方法建立。用氟化物代替氧化物，作为控制热膨胀的一种手段，是一个未探索的竞技场，具有很大的潜在有趣的发现。AX_2O_7的局域结构（A-Zr，Hf; X-P，V）的纳米结构将使用总散射进行检查，以更好地理解它们的高温相变以及纳米结构如何它们的无序高温相的（局部结构）可导致低的或负的热膨胀，因为只有这些材料的无序形式显示出令人感兴趣的膨胀特性。材料的热膨胀特性在确定其是否适用于各种应用中起着非常重要的作用。拟议的工作将导致对控制热膨胀和制备新材料的策略的进一步理解。这将是在寻找新的有用的工程材料的价值。作为这项工作的一个组成部分，研究生和本科生将接受各种合成和材料表征技术的培训，介绍材料化学/科学中的重要概念，并参与开发专业技能的活动。这些技能对美国经济具有相当大的价值。拟议实验工作的一个重要组成部分将使用位于能源部国家实验室的主要X射线和中子散射设施进行。在DOE实验室的工作增强了学生的教育经验，并导致专业上有利于大学和政府实验室员工的合作。

TECHNICAL SUMMARY:Thermal expansion plays a very important role in determining if a material will be suitable for a particular application. The proposed work will lead to an enhanced understanding of both structure property relationships in low and negative thermal expansion (NTE) materials, and strategies for controlling thermal expansion. The pressure dependence of thermal expansion (TE) in a variety of low and negative TE materials will be examined to establish the factors that lead to highly pressure dependent coefficients of thermal expansion (CTEs) in such materials. It is hypothesized that low pressure phase transitions in NTE materials will lead to the quite widespread occurrence of extreme pressure sensitivity. The pressure dependence of CTEs is a design consideration for composites where a NTE filler may experience stresses. The control of thermal expansion, by modifying the O:F ratio, in oxyfluorides with a ReO3 framework structure, will be examined and the underlying structure property relationships established by separately interrogating the response of M-F-M and M-O-M links to temperature and pressure using total scattering methods. Substitution of fluoride for oxide, as a means of controlling thermal expansion, is an unexplored arena with great potential for interesting findings. The local structures of AX2O7 (A - Zr, Hf; X - P, V) will be examined using total scattering to better understand their high temperature phase transitions and how the nanostructure (local structure) of their disordered high temperature phases can lead to low or negative thermal expansion, as only the disordered forms of these materials display interesting expansion characteristicsNON-TECHNICAL SUMMARY:The thermal expansion characteristics of a material play a very important role in determining if it is suitable for use in a wide variety of applications. The proposed work will lead to an enhanced understanding of strategies for controlling thermal expansion, and the preparation of new materials. This will be of value in the search for new useful engineering materials. As an integral part of this work, graduate and undergraduate students will be trained in a wide variety of synthetic and materials characterization techniques, introduced to important concepts in materials chemistry/science, and engaged in activities that develop professional skills. These skills are of considerable value to the US economy. A significant component of the proposed experimental work will be conducted using major x-ray and neutron scattering facilities located at Department of Energy (DOE) national laboratories. The work at DOE laboratories enhances the educational experience of students, and leads to collaborations that professionally benefit both university and government laboratory employees.