本文利用基于密度泛函理论的第一原理方法研究了典型金属有机框架材料——MOF-5的力学、电学性质及其应变调控特性.通过对MOF-5材料施加不同类型的应变,系统地研究了MOF-5材料的力学特性,获得了MOF-5的弹性常数、杨氏模量等基本力学参数.另一方面,通过分析能带结构等特征得到了MOF-5的本征电学特性,计算得到的MOF-5的禁带带宽为3.49 eV,属于宽禁带半导体.对MOF-5电学性质的应变调控特性研究发现,外界应变会显著降低MOF-5的禁带带宽,提高其导电性.通过进一步分析其电子态密度、共价键键长等的变化,发现外界应变会引起MOF-5有机配体中共价键强度的降低,继而导致材料禁带带宽的减小.研究从理论上定量揭示了外部应变对MOF-5电学性质的调控行为,为基于MOF-5的气氛传感器优化设计和性能评估等提供了重要的理论依据.%Metal-organic frameworks (MOFs) have attracted a great deal of interest from both academia and industry due to their extensive potential applications. The tunable physical properties through the manipulation of composition have led to increasing attention to the exploration of the MOF applications. However, the tunability of physical property of MOF with external mechanical load, which usually steams from actual fabrication and application processes, has been rarely investigated. Here, ab initio (first-principles) density functional theory calculations are performed to investigate the mechanical, electrical properties and strain engineering of a typical metal-organic framework, MOF-5. Preliminary calculations by using different pseudopotentials and cut-off energies are performed to verify the adopted critical param-eters in subsequent simulations. Both the structural stability of MOF-5 and the effect of applied strain are investigated from an energetic point of view. With the increase of applied strain, the cohesive energy of MOF-5 decreases, inducing the reduction of structural stability. In addition, the variation of cohesive energy of MOF-5 shows an asymmetry under expansive and compressive conditions. By applying strain along different directions, the mechanical properties of MOF-5 are systematically investigated, and mechanical constants including Young’s modulus, Poisson ratio and elastic constants are obtained. In addition, by analyzing the band gap of MOF-5, the intrinsic electrical property of MOF-5 is clarified. The band gap of MOF-5 is 3.49 eV, indicating that MOF-5 is a wide bandgap semiconductor, which is represented by the combination effect of both [Zn4O]6+ metal clusters and organic linkers. Analysis on the strain engineering of electrical properties of MOF-5 reveals that the applied strain induces the decrease of band gap of MOF-5, and thus leading to the increase of conductivity. This transition is induced by the decrease of conduction energy-level. Further studies on the variations of PDOS and covalent bond show that the strain engineering of electrical property of MOF-5 intrinsically originates from the variation of covalent bond in the organic linker. The applied strain apparently weakens the covalent bond, and thus inducing the relaxation and redistribution of electrons, which increases the activities of electrons, and finally leads to the overall increase of conductivity of MOF-5. This theoretical study quantitatively clarifies the tunability of electronic band gap of MOF-5 with external strain, and provides a theoretical guidance in the design optimization and property evaluation of gas sensors based on MOF-5.
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