CAREER: Chemical Frustration - A Guiding Principle for the Discovery and Interpretation of New Complex Intermetallic Phases

技术摘要：合成和结构研究不断揭示金属间化合物相是一个具有无与伦比的结构复杂性和多样性的领域。这种多样性的扩大速度远远超过了能够解释和预测这种结构化学的理论模型的发展速度。缺乏这样的模型是设计具有定制结构的新型金属间化合物和合金材料的一个瓶颈。最近关于复杂金属间化合物相的理论和实验研究的结果可以看出一个共同的主题，这些研究可以作为更全面的理论框架的基础。这些阶段的结构复杂性通常可以追溯到相互排斥的键合或几何堆积模式之间的竞争或共存，通过类比磁化受挫现象，这种紧张在这里被称为“化学受挫”。在SSMC/DMR计划的支持下，该项目旨在通过检查金属间化合物系统来发展这一概念，该系统旨在控制简单紧密堆积(SCP)和基于四面体的堆积(TCP)变体之间的内在张力。金属间化合物系统将用固态合成来研究，目的是发现新相、这些新相的结构分析和电子结构计算。理论上的努力将包括开发用于检测和分析竞争性化学键类型的理论工具。这些理论工具将基于应用于根据密度泛函理论(DFT)结果校准的Hück el计算的矩方法。同时，还将执行一项教育计划，包括创建固态化学网络资源库，作为国家科学数字图书馆的一部分，并为该资源库开发材料。非技术摘要：金属间化合物形成了一大类对材料科学极其重要的化合物。它们采用了各种各样的晶体结构，这一点还没有用化学键的概念来解释。缺乏了解和预测这些相的首选晶体结构的理论框架是设计具有有用的储氢、催化和超导性能的新金属材料的限制因素。在这个由SSMC/DMR支持的项目中，采取了理论和实验相结合的方法，以加深对这些相的晶体结构背后的驱动力的理解，并获得对这些结构的一定程度的控制。这种方法引出了一个在一些最复杂的金属间晶体结构中已经被察觉到的共同主题：结构的复杂性可以与在同一阶段共存的相互排斥的键合类型之间的紧张联系在一起。在这个项目中，将通过选择在首选类型的化学键和原子堆积中具有内在冲突的元素组合来诱导这种紧张，从而寻找新的化合物。这种设计新的金属间化合物结构的方法有可能促进新合金的开发，使其具有广泛的应用。预计将研究的几种化合物还具有用于储氢和超导的有用材料性能。这项工作的教育和社会影响也将是巨大的：该项目将包括创建固态化学网络资源库，这是一个为化学教师和讲师提供教育材料的储存库，他们有兴趣将当前材料科学的主题纳入他们的课堂。该项目将通过代表人数不足的群体成员的参与来促进科学多样性。

TECHNICAL SUMMARY: Synthetic and structural studies are continuously revealing intermetallic phases to be a domain of unparalleled structural complexity and diversity. The rate at which this diversity is expanding far exceeds that of the development of theoretical models capable of accounting for and making predictions regarding this structural chemistry. The absence of such models is a bottleneck in the design of new intermetallic and alloy materials with tailored structures. A common theme can be perceived in the results of recent theoretical and experimental studies on complex intermetallic phases that may serve as the basis for a more comprehensive theoretical framework. Structural complexity in these phases can often be traced to a competition between or coexistence of mutually exclusive bonding or geometrical packing modes, a tension referred to here as "chemical frustration", by analogy with the phenomenon of magnetic frustration. Under the support of the SSMC/DMR program, this project aims to develop this concept through the examination of intermetallic systems designed to contain inherent tensions between variants on simple close-packing (SCP) and tetrahedra-based packing (TCP). Intermetallic systems will be studied with solid state synthesis aimed at the discovery of new phases, the structural analysis of these new phases, and electronic structure calculations. The theoretical efforts will include the development of theoretical tools designed for the detection and analysis of competing chemical bonding types. These theoretical tools will be based on the Moments Method applied to Hückel calculations calibrated against Density Functional Theory (DFT) results. In parallel, an education plan will be pursued involving the creation of the Solid State Chemistry Web Resource Library as part of the National Science Digital Library, as well as the development of materials for this library.NON-TECHNICAL SUMMARY: Intermetallic phases form a broad family of compounds of immense importance to materials science. They adopt a diverse array of crystal structures that has yet to be accounted for with chemical bonding concepts. The absence of a theoretical framework for understanding and predicting the preferred crystal structures of these phases is a limiting factor in the design of new metallic materials with useful properties for hydrogen storage, catalysis, and superconductivity. In this SSMC/DMR-supported project, a joint theoretical and experiment approach is taken to develop understanding the driving forces underlying the crystal structures of these phases, and to gain some degree of control over these structures. The approach draws a common theme that has been perceived in some of the most complex intermetallic crystal structures: structural complexity can be linked to a tension between mutually exclusive bonding types coexisting in the same phase. In this project, new compounds will be sought out by inducing such tension through the selection of combinations of elements with inherent conflicts in the preferred types of chemical bonding and atomic packing. This approach to the design of new intermetallic structures has the potential of facilitating the development of new alloys for a wide range of applications. Several of the compounds to be investigated are also anticipated to have useful materials properties for hydrogen storage and superconductivity. The educational and social impacts of this work will also be considerable: the project will include the creation of the Solid State Chemistry Web Resource Library, a repository of educational materials for chemistry teachers and instructors interested in including current topics in materials science in their classes. The project will promote diversity in science through the participation of members of underrepresented groups.