Structural Plasticity in Intermetallics: Shaping the Crystal Structures of Metals and Alloys with Chemical Pressure

技术概述金属间化合物相结合了多样化的结构化学和一系列有价值的物理和化学性质，包括超导、热电、储氢、催化和各种磁现象。从这些化合物中开发材料的一个限制因素是在试图合成指导或控制它们的晶体结构时遇到的困难。该项目由固态和材料化学(SSMC)计划支持，重点是开发一个新的概念框架，以了解和利用金属间晶体结构背后的化学驱动力：结构可塑性。许多复杂的金属间化合物相的结构可以看作是由更简单的结构类型的碎片组成的，这些碎片被界面分开。这种原子排列使人回想起机械应力在可锻性金属中引起的位错，并调节金属对这种应力的反应。结构塑性模型假设金属间化合物和可塑性金属之间的联系超出了几何范围：将界面插入到简单结构中以创建更复杂的结构，以缓解如果以未经修改的形式采用原始结构将存在的内应力。本项目采用理论计算和实验工作相结合的方法来探索这一假说。这包括密度泛函理论-化学压力(DFT-CP)分析的开发和应用，该分析从DFT结果中提取作用于晶体结构中单个原子的局部压力或化学压力的信息。化学压力分析和经验推理的结果被用于由化学压力诱导的结构塑性所产生的新的金属间化合物结构的合成和结构确定。通过这种理论和实验相结合的方法，将探索结构应对化学压力的三种机制：(1)在简单结构类型中插入缺陷面，(2)由一种结构类型托管另一种结构类型，以及(3)准晶有序的形成。非技术性材料和合金表现出许多有用的性质，有望在能源应用中发挥关键作用，如储存氢作为燃料来源，催化燃料电池电极上的化学反应，以及从温度梯度中提取电能。由于难以控制这些材料中原子的堆积几何形状，将这些性质优化应用变得非常复杂。这项由固态与材料化学(SSMC)计划支持的研究项目的中心目标是了解化学键如何决定这些原子排列，以及基于这些见解定制原子堆积以提高所需材料性能的策略。这一目标将通过将理论和计算模拟与新材料的合成和表征相结合来实现。该项目还包括创建和扩大在线资源，以促进将材料化学纳入高中和本科课程。这些资源包括固态化学资源库和在线教科书《交互式固态化学》。总而言之，这些将有助于将丰富的在线内容系统化，作为固体和材料化学的教学助手，并将填补现有内容在这些主题覆盖方面的空白。两者都将被纳入化学教育数字图书馆，这是国家科学数字图书馆的一条途径。

TECHNICAL SUMMARYIntermetallic phases combine a diverse structural chemistry with a range of valuable physical and chemical properties, including superconductivity, thermoelectric, hydrogen storage, catalysis, and a variety of magnetic phenomena. A limiting factor in the development of materials from these compounds is the difficulty encountered when attempting to synthetically guide or control their crystal structures. The focus of this project supported by the Solid State and Materials Chemistry (SSMC) program is the development of a new conceptual framework for understanding and harnessing the chemical driving forces underlying intermetallic crystal structures: Structural Plasticity. The structures of many complex intermetallic phases can be viewed as being built from fragments of simpler structure types, which are separated by interfaces. Such atomic arrangements recall the dislocations that are induced by mechanical stress in a malleable metal and mediate a metal's response to such stress. The structural plasticity model hypothesizes that the connection between intermetallics and malleable metals goes beyond geometry: interfaces inserted into a simple structure to create a more complex one alleviate internal stresses that would be present if that original structure were to be adopted in an unmodified form. This project uses a combination of theoretical calculations and experimental work to explore this hypothesis. This includes the development and application of the Density Functional Theory-Chemical Pressure (DFT-CP) analysis, which extracts information about the local pressures, or chemical pressures, acting on individual atoms within a crystal structure from DFT results. The results of chemical pressure analysis and empirical reasoning are used in the synthesis and structure determination of new intermetallic structures that emerge from chemical pressure-induced Structural Plasticity. Three mechanisms by which structures cope with chemical pressure will be explored through this joint theoretical and experimental approach: (1) the insertion of defect planes into a simple structure type, (2) the hosting of one structure type by another, and (3) the formation of quasicrystalline order. NON-TECHNICAL SUMMARYMetals and alloys exhibit a host of useful properties that are expected to play key roles in energy applications, such as storage of hydrogen as a fuel source, the catalysis of chemical reactions at fuel cell electrodes, and the extraction of electrical energy from temperature gradients. Optimizing these properties for applications is severely complicated by the difficulty of controlling the packing geometries of atoms in these materials. The central goal of this research project supported by the Solid State and Materials Chemistry (SSMC) program is to develop an understanding how the chemical bonding determines these atomic arrangements, and strategies based on these insights for tailoring atomic packing to enhance the desired materials properties. This objective will be attained through combining theoretical and computational modeling with the synthesis and characterization of new materials. The project also includes the creation and expansion of online resources for facilitating the incorporation of materials chemistry into high school and undergraduate courses. Included among these resources are the Solid State Chemistry Resource Library and the online textbook Interactive Solid State Chemistry. Together, these will help systematize the wealth of on-line content available as teaching aides for solid state and materials chemistry, and will fill gaps in the coverage of these subjects left by the existing content. Both are to be incorporated in the Chemical Education Digital Library, a pathway in the National Science Digital Library.