arXiv 2011.137652020-11-27cond-mat.mtrl-sci

混合钙钛矿、金属-有机框架及其他：分子框架中的非常规自由度

Hybrid Perovskites, Metal--Organic Frameworks, and Beyond: Unconventional Degrees of Freedom in Molecular Frameworks

Hanna L. B. Boström, Andrew L. Goodwin

摘要：

材料的结构自由度是由外部刺激最直接激活的各种扭曲。在材料化学中，一个非常成功的设计策略就是控制这些个别的扭曲，以产生有用的功能反应。例如，在钛酸铅等铁电体中，关键的自由度涉及Pb $^{2+}$的位移;通过将这些耦合在一起，系统与电场相互作用。一个令人兴奋的发展是利用不同扭曲之间的相互作用：$e.g.$通过结合不同的多面体旋转产生偏振。因此，自由度作为几何“元素”，可以结合工程材料与有趣的属性。正如新元素的发现使化学空间多样化一样，识别新型结构自由度是开发新功能材料的关键策略。在这种情况下，分子框架是一个肥沃的来源，意想不到的失真类型，其中许多没有平行的传统固态化学。骨架材料是固体，其结构由节点和接头组装而成，形成支架状网络。这些结构通常包含空腔，其可以容纳用于电荷平衡的额外离子。在已建立的系统中-如钛酸铅-这些成分都是原子，但在分子框架中，至少有一个离子是分子。在这里，我们调查的非常规自由度通过分子取代原子。我们的动机是了解这些新的扭曲在不同材料特性中的作用。在实验示例的背景下总结和描述了各种自由度。我们强调了一些未来研究的方向，这表明了这个新兴领域的非凡的可能性。

英文摘要：

The structural degrees of freedom of a material are the various distortions most straightforwardly activated by external stimuli. A highly successful design strategy in materials chemistry involves controlling these individual distortions to produce useful functional responses. In a ferroelectric such as lead titanate, for example, the key degree of freedom involves displacements of Pb$^{2+}$; by coupling these together, the system interacts with electric fields. An exciting development has been to exploit the interplay between different distortions: $e.g.$ generating polarisation by combining different polyhedral rotations. Thus, degrees of freedom act as geometric `elements' that can be combined to engineer materials with interesting properties. Just as the discovery of new elements diversified chemical space, identifying new types of structural degrees of freedom is a key strategy for developing new functional materials. In this context, molecular frameworks are a fertile source of unanticipated distortion types, many of which have no parallel in conventional solid-state chemistry. Framework materials are solids whose structures are assembled from nodes and linkers to form scaffolding-like networks. These structures usually contain cavities, which may host additional ions for charge balance. In the well-established systems---such as lead titanate---these components are all atomic, but in molecular frameworks, at least one ion is molecular. Here, we survey the unconventional degrees of freedom introduced through the replacement of atoms by molecules. Our motivation is to understand the role these new distortions play in different materials properties. The various degrees of freedom are summarised and described in the context of experimental examples. We highlight a number of directions for future research, which demonstrate the extraordinary possibilities for this nascent field.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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英文摘要：

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