Research On The Electronic Structure And Chemical Bonding Of Metal-doped Boron Clusters And Materials

Boron materials and boron compounds are widely used in the applications on materials,chemical industry,aerospace,medical fields,such as superhard materials,semiconductor electronic devices and biological compounds with antibacterial and antiviral properties.Boron materials demonstrate diverse structures,most of which are composed of B₁₂ icosahedron,and have four different kinds of rhombic hexahedron for pure element phases.The successful synthesis of two-dimensional boron materials in2015 has provided a foundation for the design and development of new boron materials and opened the door for the research on boron based two-dimensional materials.Compared with carbon,boron clusters are lack of investigations,which is due to the bonding complexity caused by electron deficiency of boron and the structural diversity of boron clusters with the growth of size.The order of magnitude of clusters is generally in the nanometer range,which can show strong quantum effect and lead to the emergence of many new phenomena.Therefore,it is crucial to systematically study the structural and the chemical bonding characteristics of size-specific boron clusters by quantum chemical calculations to reveal the unique bonding mechanism and understand the properties of boron materials.Due to the electron deficiency,boron clusters are more susceptible to be doped by electron-rich metals,so as to balance the electron distribution and maintain the stability of the system.Different types of metals and specific doping forms enrich the diversity of geometric structure,electronic structure and bonding mechanism.In this thesis,we have constructed a series of different metal-doped boron clusters.The thermodynamic stability of the structure was verified by the global minimum search program.Based on various bonding analysis methods,the electronic structure and the chemical interaction were thoroughly studied.Then,we extend the stable unitary structure to 2D or 3D to explore the potential applications in metal-doped boron materials.Three main achievements are summarized as the following content:1)Analogous with carbon nanotubes and fullerenes,the transition-metal doped boron-nanotubes(Mn B^-₁₆,Ta B^-₂₀)and borophene-like clusters(Co B^-₁₈,Rh B^-₁₈)have been fabricated,which enrich the structural diversity of boron clusters.The chemical interaction between the doped metal and boron framework and the inherent stability of the system were investigated based on density functional theory and wave functional methods.These stable clusters with high symmetry are expected to be the unitary structures for t he new metal-doped boron nanomaterials.2)Lanthanide elements generally have 4f unpaired electrons so that can be served as the dopants into boron clusters.Single lanthanide atom doping and double lanthanide atom doping have been studied successively,which has enriched the understanding of the electronic structure o f metal-boron compounds and the related solid materials.Different kinds of metal dopants can not only balance the electronic distribution of boron materials,but also be expected to improve new materials with excellent magnetic,optical and catalytic properties.3)It is important to establish a n efficient bridge between the gas-phase compounds and solid material for better understanding of both systems.We have proposed a rational relationship between Ln₂B₈ and Ln B₆ species on the perspectives of geometries,electronic structure s and bonding patterns.It provides a unique perspective to analyze the stability for both gaseous complexes and solid-state materials.