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

非技术概述：金属间相是一类金属和合金，表现出广泛的材料性能，对技术应用有价值。例如，催化化学合成或产生能量的反应，将温度梯度转化为电能，维持强大和永久的磁矩，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，解决这个问题可以允许合理的方法来增强这些性质。本研究的重点是由材料研究部固态和材料化学（SSMC）项目支持的原子排列和金属间化合物材料行为之间的这种联系的发展。理论方法用于预测这些化合物的原子几何形状、由这些结构产生的物理性质以及它们对压力或温度变化的反应。实验包括创造新材料和测量它们的性质，然后用来测试这些预测和修改理论模型。此外，本项目涉及固态和材料化学教学资源的开发，这是本科课程中代表性不足的学科。在线教科书“互动固态化学”的新内容正在开发中，它利用网页格式的互动能力来增强学生对材料的体验。通过将其作为化学教育数字图书馆（国家科学数字图书馆的一个途径）的生活教科书，广泛的教育工作者和学生可以使用该资源。通过制作Science through Comics网站，也促进了对材料化学的兴趣和认识，该网站以非技术和幽默的方式说明了该领域的各个方面。技术概述：金属间相包括一个广泛的固体材料家族，其结构多样性和丰富的物理性质范围都是显著的。因此，金属间化合物在材料设计工作中显示出巨大的希望，其中调整结构特征以优化特定性能。然而，实现这种潜力的一个限制因素是，它们通常复杂的原子排列与它们所表现出的物理性质之间需要明确的关系。在NSF之前的支持下，一种理论方法被开发出来，提供了一种连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）计算的输出用于构建固态结构内的局部压力图，这揭示了电子相互作用和原子堆积约束之间的冲突如何成为金属相中广泛结构现象的基础。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概念框架中，该框架不仅考虑了金属间化合物的结构趋势，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统一理解金属间化合物的结构和性质，并将其应用于材料设计。这一目标的进展是通过将DFT-CP方法应用于实验设计的三个子项目来实现的：(1)由CP释放驱动的新结构化学的合成探索，(2)将结构与振动特性联系起来的原理的开发和验证，振动特性反过来影响热稳定性、导热性和超导性等物理特性，以及(3)发现新的压力诱导的结构转变。第一个子项目涉及由CP计算驱动的金属间系统的合成，确定新遇到的结构，并使用数据挖掘和理论将这些结构放入家族树中，其分支表示CP释放的途径。第二个和第三个子项目分别利用阿贡国家实验室核共振非弹性x射线散射（NRIXS）和高压同步加速器x射线衍射测量的先进光子源的专业知识和设施来验证理论预测。

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.