Confronting Complexity in Intermetallics: A Synthetic, Structural and Theoretical Approach

本项目涉及两种金属结构基元（贵金属-黄铜上层结构）之间存在晶格不匹配的相，可以分解为更简单组分的大立方相，由同心二十面体对称团簇组成的相和由扩展的缺电子团簇组成的结构。所有这些系统都位于金属-绝缘体边界附近，有些在一边，有些在另一边，具有复杂的结垢特性，并且可能包含更多金属（共价）和更多离子成分之间的界面。它们测试了目前用于纯金属、绝缘体或半导体的范例的边界。参与本项目的学生将学习如何应用现代电子结构计算来理解复杂的晶体结构，这些结构现在可以通过现代同步辐射衍射实验获得。非技术解释文明的经典合金，黄铜和青铜，元素，铜，银和金是拟议项目的核心。我们今天对它们结构的理解仍然明显地植根于古典观念：例如柏拉图式的多面体。该项目旨在对这些结构及其衍生的其他结构进行连贯的结构改造。这将是一个从经典几何图像（例如，仍然用于理解γ -黄铜的结构）到基于简单量子力学计算的范式的改造。预计这种理解将演变为基于最小表面和互锁相互啮合子结构的模型。我们之所以选择这些材料，不仅是因为它们迄今为止被证明是难以理解的，而且还因为我们认为这些材料具有不同寻常的键合趋势平衡，这很可能导致材料具有新的特性，如离子和金属成分之间的分离，亚晶格剪切模式，这些特性会影响这些基本合金的电、磁和内聚特性。

TECHNICAL EXPLANATION This project addresses the synthesis, structural characterization, properties, and band calculations for, are phases in which there are lattice mismatches between two metal structural motifs (noble metal gamma-brass superstructures), large cubic phases which can be decomposed into simpler components, phases composed of concentric icosahedral symmetry clusters, and structures composed of extended electron deficient clusters. All these systems lay near the metal-insulator boundary, some on one side, some on the other, have complex scaling properties, and potentially contain interfaces between their more metallic (covalent) and more ionic components. They test the boundaries of current paradigms useful for pure metals, insulators or semiconductors. Students working on this project will learn how to apply modern electronic structure calculations to understand the complex crystal structures that can now be obtained through modern synchrotron radiation diffraction experiments.NON-TECHNICAL EXPLANATIONThe classic alloys of civilization, brass and bronze, the elements, copper silver and gold lie at the heart of the proposed project. Our understanding today of their structures is remarkably still often imbedded in classical notions: the Platonic polyhedra for example. This project aims at a coherent structural reworking of these structures and the other structures derived from them. It will be a reworking from a classical geometrical picture (still used in understanding structures of gamma-brass for example), to paradigms based on simple quantum mechanical calculations. It is anticipated that the understanding will evolve into models based on minimal surfaces and interlocking intermeshed substructures. The materials being studied are chosen not just because they have hitherto proven difficult to understand but also because we think that such materials possess an unusual balance of bonding trends that could very well lead to materials with novel properties such as segregation between ionic and metallic components , and sub-lattice shear patterns, properties which affect the electrical and magnetic and cohesion properties of these essential alloys.