论文标题
晶体金属有机框架中类似玻璃的热导率的起源
The Origin of the Glass-like Thermal Conductivity in Crystalline Metal-Organic Frameworks
论文作者
论文摘要
教科书认为，声子，即传播晶格波的能量量子是完美晶体中的主要热载体。结果，在许多晶体中，例如散装硅，温度依赖性的导热率显示了经典的1/t关系，因为系统中的主要UMKLAPP声子 - Phonon散射。但是，许多结晶金属有机框架的导热率非常低，并且表现为否，较弱的阴性，甚至是弱的正温度依赖性（玻璃样的导热率）。它一直在争论中是否可以用金属有机框架中的声子描述热传输。在这里，通过研究两个典型系统，即晶体沸石咪唑酸盐框架-4（CZIF-4）和晶体沸石咪唑酸酯框架-62（C-ZIF62），我们证明，金属 - 有机框架中的超强度范围内的cav范围差异很大，并且由于较大的范围差异而导致金属有机框架中的超导热性，以及较大的cav群体差异。我们的平均自由路径频谱分析表明，系统中存在传播和非传播的非谐波振动模式，并在很大程度上有助于导热率。热导率的相应的弱负温度依赖性是源自传播和非传播的非谐振动模式之间的竞争。我们在这里的研究提供了对金属有机框架中热传输的基本了解，并将使用金属有机框架（例如，易燃气体存储，化学催化，太阳能热转化等）指导与热相关的应用的设计。
It is textbookly regarded that phonons, i.e., an energy quantum of propagating lattice waves, are the main heat carriers in perfect crystals. As a result, in many crystals, e.g., bulk silicon, the temperature-dependent thermal conductivity shows the classical 1/T relationship because of the dominant Umklapp phonon-phonon scattering in the systems. However, the thermal conductivity of many crystalline metal-organic frameworks is very low and shows no, a weakly negative and even a weakly positive temperature dependence (glass-like thermal conductivity). It has been in debate whether the thermal transport can be still described by phonons in metal-organic frameworks. Here, by studying two typical systems, i.e., crystal zeolitic imidazolate framework-4 (cZIF-4) and crystal zeolitic imidazolate framework-62 (c-ZIF62), we prove that the ultralow thermal conductivity in metal-organic frameworks is resulting from the strong phonon intrinsic structure scattering due to the large mass difference and the large cavity between Zn and N atoms. Our mean free path spectrum analysis shows that both propagating and non-propagating anharmonic vibrational modes exist in the systems, and contribute largely to the thermal conductivity. The corresponding weakly negative or positive temperature dependence of the thermal conductivity is stemming from the competition between the propagating and non-propagating anharmonic vibrational modes. Our study here provides a fundamental understanding of thermal transport in metal-organic frameworks and will guide the design of the thermal-related applications using metal-organic frameworks, e.g., inflammable gas storage, chemical catalysis, solar thermal conversion and so on.
