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

技术概述：热膨胀在确定材料是否适合特定应用方面起着非常重要的作用。所提出的工作将有助于加深对低热膨胀和负热膨胀（NTE）材料的结构性质关系的理解，以及控制热膨胀的策略。将研究各种低和负热膨胀材料中热膨胀（TE）的压力依赖关系，以确定导致此类材料中热膨胀（cte）的高压依赖系数的因素。假设NTE材料中的低压相变将导致相当广泛的极端压力敏感性的发生。cte的压力依赖性是复合材料的设计考虑因素，其中NTE填料可能经历应力。通过改变O:F比来控制具有ReO3骨架结构的氟氧化物的热膨胀，并通过使用总散射方法分别询问M-F-M和M-O-M链对温度和压力的响应来建立潜在的结构性质关系。以氟化物取代氧化物作为控制热膨胀的一种手段，是一个尚未开发的领域，极有可能产生有趣的发现。AX2O7 (A - Zr, Hf；X - P， V)将使用总散射来检查，以更好地了解它们的高温相变以及它们无序高温相的纳米结构（局部结构）如何导致低热膨胀或负热膨胀。摘要：材料的热膨胀特性在决定它是否适合于各种各样的应用方面起着非常重要的作用。所提出的工作将导致对控制热膨胀和制备新材料的策略的更好理解。这对寻找新的有用的工程材料是有价值的。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/科学的重要概念，并参与培养专业技能的活动。这些技能对美国经济具有相当大的价值。拟议的实验工作的一个重要组成部分将使用位于能源部（DOE）国家实验室的主要x射线和中子散射设备进行。美国能源部实验室的工作提高了学生的教育经验，并促成了大学和政府实验室员工的专业合作。

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.