Structure and Dynamics of Framework Inorganic Materials

本提案旨在理解和发展一些由单晶硅多面体（即金属M，被n个氧原子包围）组成的迷人无机材料的化学性质，通过它们的顶点连接在一起形成一个连续的结构。我们感兴趣的特殊材料常常表现出极不寻常的负热膨胀现象。这些材料不是随着温度的升高而膨胀（热振动的增加往往会增加键长），而是收缩。此外，我们已经证明，在这些材料中，氧原子经常在非常低的温度下运动。了解氧原子如何在材料中运动具有很大的技术兴趣；氧化离子导体是燃料电池等替代能源的关键部件。寻找能让氧气在低温下穿过这种结构的材料是一项重大挑战。现代化学是跨学科的，提出的工作也不例外；我们将开发合成新材料和化合物的方法，并使用各种互补的分析技术来了解它们是如何工作的。我们一直在开发复杂的合成策略，使我们能够通过相对温和的加热过程将预先安排的前体转化为特定的目标材料。在开发了这些路线之后，我们渴望看到可以生产出哪些其他新材料。这项工作真正具有挑战性的方面在于这些材料的结构和运动的特征。它们的行为复杂而有趣。在高温下，结构相对简单且高度对称。然而，随着温度的降低，它们的许多结构扭曲，并且单位胞（重复结构基序）变得非常大（在一种情况下有1000个原子！）。最根本的是，形成了不同的低温结构，尽管起始材料表面上很相似。理解为什么一种特定的材料形成一种特定的结构而不是另一种是一个基本问题。确定这些复杂的结构是极具挑战性的：没有一种技术能提供所有的答案。我们将同时使用衍射和固体核磁共振来解决这个问题，衍射和固体核磁共振是研究长程结构的，固体核磁共振是对局部结构敏感的。虽然一些研究小组已经使用了来自核磁共振的明显信息（例如，单位细胞中不同位点的数量），但我们建议将这两种互补技术适当地结合起来。我们的中心思想是使用最新的计算计算将结构的特定局部特征与它们的核磁共振谱联系起来。然后，例如，当从衍射数据求解结构时，我们可以使用核磁共振信息作为约束。即使有了这些信息，解决如此复杂的结构仍将是一个挑战。幸运的是，我们有一些有希望的想法来提高结构解决方案的效率。这笔拨款不仅将使我们能够发展一些令人着迷的新化学，而且还将把两种截然不同但互补的分析技术的力量结合起来，解决材料科学中的一些基本问题

This proposal seeks to understand and develop the chemistry of some fascinating inorganic materials which consist of MOn polyhedra (i.e. a metal, M, surrounded by n oxygen atoms), linked together through their vertices to form a continuous structure. The particular materials we are interested in often show the highly unusual phenomenon of negative thermal expansion . Rather than expanding as the temperature is increased (increasing thermal vibrations tend to increase bond lengths), these materials contract. In addition, we've shown that the oxygen atoms are often in motion at remarkably low temperatures in these materials. Understanding how oxygen atoms move in materials is of great technological interest; oxide-ion conductors are key components of alternative energy sources such as fuel cells. Finding materials that allow oxygen to move through the structure at low temperatures is a major challenge.Modern chemistry is inter-disciplinary, and the proposed work is no exception; we will be developing ways to synthesise new materials and compounds and using a variety of complementary analytical techniques to understand how they work. We have been developing sophisticated synthetic strategies that allow us to transform pre-arranged precursors to specific target materials via a relatively gentle heating process. Having developed these routes, we are keen to see what other new materials can be produced.The really challenging aspects to this work lie in the characterisation of the structure and motion in these materials. Their behaviour is complex and intriguing. At high temperatures the structures are relatively simple and highly symmetric. As the temperature is reduced, however, many of their structures distort and the unit cell (repeating structural motif) becomes very large (>1000 atoms in one case!). Most fundamentally, different low temperature structures are formed, despite the apparent similarity of the starting materials. Understanding why a particular material forms a particular structure and not another is a fundamental question. Determining these complex structures is extremely challenging: no one technique provides all the answers. We will use both diffraction, which looks at the long-range structure, and solid-state NMR, which is sensitive to the local structure, to tackle the problem.Although several research groups have used the obvious information from NMR (e.g. number of distinct sites in the unit cell), we are proposing to properly integrate these two complementary techniques. Our central idea is to use the latest computational calculations to link specific local features of the structures to their NMR spectrum. We can then, for instance, use the NMR information as constraints when solving the structure from diffraction data. Even with this information, solving such complex structures will be a challenge. Fortunately we have some promising ideas for improving the efficiency of the structure solution.The award of this grant would not only allow us to develop some fascinating new chemistry, but it would bring the power of two very different, but complementary, analytical techniques together to solve some fundamental problems in materials science