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

技术摘要：热膨胀在确定一种材料是否适合特定应用方面起着非常重要的作用。这项拟议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以及控制热膨胀的策略的理解。我们将研究各种低膨胀和负膨胀材料的热膨胀系数与压力的关系，以确定导致此类材料热膨胀系数高度依赖于压力的因素。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。对于NTE填充物可能承受应力的复合材料，CTE的压力依赖性是一个设计考虑因素。通过改变O：F比，对具有稀土骨架结构的氟氧化合物的热膨胀控制进行了研究，并通过使用总散射方法分别询问M-F-M和M-O-M对温度和压力的响应来建立潜在的结构性质关系。用氟化物代替氧化物作为一种控制热膨胀的方法，是一个未被探索的领域，有很大的潜力获得有趣的发现。AX2O7(A-Zr，Hf；X-P，V)的局域结构将用全散射来研究，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(局域结构)如何导致低或负的热膨胀，因为只有这些材料的无序形式才表现出有趣的膨胀特性非技术摘要：材料的热膨胀特性在确定它是否适合于广泛的应用中起着非常重要的作用。拟议的工作将使人们更好地理解控制热膨胀的战略，以及新材料的制备。这对寻找新的有用的工程材料将是有价值的。作为这项工作的组成部分，研究生和本科生将接受各种合成和材料表征技术的培训，了解材料化学/科学中的重要概念，并参与发展专业技能的活动。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利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。美国能源部实验室的工作增强了学生的教育体验，并促成了合作，使大学和政府实验室的员工都在专业上受益。

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.