Perceiving Function in Geometrical Beauty: Chemical Pressure as a Link between Structure and Properties in Intermetallics

非技术总结：金属间相是一类金属和合金，表现出广泛的材料行为，对技术应用有价值。 例子包括催化化学合成或能量产生的反应，将温度梯度转化为电能，保持强和永久的磁矩，以及在剧烈的机械变形后恢复原始几何形状的能力。 一个紧迫的问题是将这些理想的行为与金属间化合物中通常复杂的原子排列联系起来，解决方案可以允许合理的方法来提高这些性能。 由材料研究部的固态和材料化学（SSMC）计划支持的这项研究的重点是发展金属间化合物的原子排列和材料行为之间的这种联系。 理论方法用于预测这些化合物中的原子几何形状，这些结构产生的物理性质，以及它们对压力或温度变化的响应。 然后，使用涉及创建新材料及其性能测量的实验来测试这些预测并修改理论模型。 此外，该项目还涉及固态和材料化学教学资源的开发，这是一个在本科课程中通常代表性不足的主题。 正在为在线教科书《互动固态化学》开发新内容，该教科书利用网页格式的互动能力，以增强学生对材料的体验。 这一资源可供广大教育工作者和学生通过其作为一个活的教科书列入化学教育数字图书馆，在国家科学数字图书馆的途径。 材料化学的兴趣和意识也通过制作科学漫画来促进，该网站以非技术和幽默的方式说明了该领域的各个方面。 金属间化合物相包括一个广泛的固态材料家族，其结构多样性和丰富的物理性能都是显著的。 因此，金属间化合物显示出很大的希望，材料的设计工作，其中的结构特征进行调整，以优化特定的性能。 然而，实现这种潜力的一个限制因素是需要在它们通常复杂的原子排列和它们所表现出的物理性质之间建立明确的关系。 在先前NSF的支持下，开发了一种理论方法，提供了一种桥接金属间化合物这些方面的方法：化学压力（CP）分析。 在这种方法中，密度泛函理论（DFT）计算的输出被用来构建固态结构内的局部压力的地图，这揭示了电子相互作用和原子堆积约束之间的冲突是如何在金属相的结构现象的基础广泛。 在这个由固态和材料化学（SSMC）计划支持的项目中，CP方法被构建到一个预测性的概念框架中，该框架不仅考虑了金属间化合物的结构趋势，而且还考虑了它们在高温和高压下的性质和相变。 本研究的最终目标是对金属间化合物的结构和性能有一个统一的认识，并能应用于材料设计。 正在通过三个子项目使DFT-CP方法适用于实验设计来实现这一目标：（1）由CP浮雕驱动的新结构化学的综合探索，（2）将结构与振动性质联系起来的原理的发展和验证，这些原理反过来影响诸如热稳定性、导热性和超导性等物理性质，（3）发现了新的压力诱导结构转变。 第一个子项目涉及的CP计算，新遇到的结构的确定，并使用数据挖掘和理论，将这些结构到家庭树的分支代表CP释放的途径，在金属间化合物系统的合成。 第二和第三个子项目分别利用阿贡国家实验室先进光子源的核共振非弹性X射线散射（NRIXS）和高压同步加速器X射线衍射测量的专业知识和设施，以验证理论预测。

NON-TECHNICAL SUMMARY:Intermetallic phases are a class of metals and alloys that exhibit a vast range of materials behaviors valuable for technological applications. Examples include the catalysis of reactions for chemical synthesis or energy generation, the conversion of temperature gradients into electrical energy, the maintenance of strong and permanent magnetic moments, and the ability to recover an original geometry after drastic mechanical deformations. A pressing problem is relating these desirable behaviors to the often complex atomic arrangements within intermetallics, the solution to which could allow rational approaches to enhancing these properties. The focus of this research supported by the Solid State and Materials Chemistry (SSMC) program in the Division of Materials Research is the development of such connections between atomic arrangements and materials behavior for intermetallics. Theoretical methods are used to make predictions about atomic geometries within these compounds, the physical properties arising from these structures, and their responses to changes in pressure or temperature. Experiments involving the creation of new materials and the measurement of their properties are then used to test these predictions and revise the theoretical models. In addition, this project involves the development of resources for teaching solid state and materials chemistry, a subject typically underrepresented in the undergraduate curriculum. New content is being developed for the online textbook Interactive Solid State Chemistry, which harnesses the interactive capabilities of the webpage format to enhance students' experience of the material. This resource is available to a broad range of educators and students through its inclusion as a Living Textbook in the Chemical Education Digital Library, a pathway in the National Science Digital Library. Interest and awareness of materials chemistry is also promoted through the production of Science Through Comics, a website in which aspects of the field are illustrated in a non-technical and humorous way. TECHNICAL SUMMARY:Intermetallic phases comprise a broad family of solid state materials that are remarkable for both their structural diversity and rich range of physical properties. Intermetallics thus show great promise for materials design efforts, in which structural features are adjusted for the optimization of particular properties. A limiting factor in realizing this potential, however, is the need for clear relationships between their often complex atomic arrangements and the physical properties they exhibit. Under prior NSF support, a theoretical method was developed that offers a way of bridging these aspects of intermetallics: Chemical Pressure (CP) analysis. In this approach, the output of density functional theory (DFT) calculations is used to construct maps of the local pressures within solid state structures, which reveal how conflicts between electronic interactions and atomic packing constraints underlie a broad range of structural phenomena in metallic phases. In this project supported by the Solid State and Materials Chemistry (SSMC) program, the CP approach is built into a predictive conceptual framework that accounts not only for structural trends within intermetallics, but also their properties and phase transitions at high temperatures and pressures. The ultimate goal of this research is a unified understanding of structures and properties in intermetallics, which can be applied in materials design. Progress toward this aim is being achieved through three subprojects adapting the DFT-CP method to experimental design: (1) the synthetic exploration of new structural chemistry driven by CP relief, (2) the development and validation of principles connecting structure to vibrational properties, which in turn influence such physical properties as thermal stability, thermal conductivity, and superconductivity, and (3) the discovery of new pressure-induced structural transformations. The first subproject involves the synthesis in intermetallic systems motivated by CP calculations, the determination of newly encountered structures, and the use of data-mining and theory to place these structures into family trees whose branches represent pathways for CP release. The second and third subprojects leverage expertise and facilities available at the Advanced Photon Source at Argonne National Laboratory for Nuclear Resonant Inelastic X-ray Scattering (NRIXS) and high pressure synchrotron X-ray diffraction measurements, respectively, to verify the predictions of theory.