Fe-B和C-N超硬材料光学性质的第一性原理研究

发布时间：2018-04-06 03:15

本文选题：第一性原理　切入点：密度泛函理论　出处：《鲁东大学》2017年硕士论文

【摘要】：Fe-B体系,C-N体系超硬材料在力学性质方面具有潜在的应用价值。在过去几十年中,对于两种体系的在力学、磁学和电学方面的理论与实验研究不断跟进,但在光学性质方面的研究较少。因此我们利用第一性原理下的多体微扰理论和密度泛函理论方法分别对Fe-B体系和C-N体系的光学性质进行研究。利用GGA+PBE方法研究了tP10-FeB4、I41/acd-FeB4和oP12-FeB2三种结构的晶体结构、能带结构和态密度等电子结构特征。进一步运用GW+BSE方法研究分析了其光学性质。结构表明oP12-FeB2能隙小,在吸收系数上表现为在可见光区出现明显的吸收峰,可用作光学吸收材料;而t P10-FeB4和I41/acd-FeB4由于能隙较宽且在禁带两端轨道占据较少,吸收表现出在紫外吸收较强,而在可见光区吸收非常小。利用密度泛函理论的GGA+PBE方法对C-N体系的十一种结构进行了研究。具体分析了晶体结构参数,电子的跃迁机理,介电函数峰的成因和光学性质。通过光学性质我们对所有结构进行了比较。根据不同结构的光学特点,加之其本身的力学特性,我们对这类结构材料的潜在应用进行了初步的预测。在C-N体系中选取了I2d-CN2结构进行Ti的掺杂研究。通过不同替换方式和调节掺杂浓度,分析比较了Ti替换N和Ti替换C元素的结构参数,电子结构,光学性质和力学性质。由于外层电子数不同,Ti替换N产生自旋极化现象,使得光学性质发生明显变化。吸收系数表明,Ti替换N元素在可见光区吸收较强且在可见光区吸收明显强于Ti替换C元素。综合这些掺杂结构的力学和光学性质,我们确定了获得两种最佳性质的掺杂浓度。
[Abstract]:The superhard materials of Fe-B system and C-N system have potential application value in mechanical properties.In the past few decades, the theoretical and experimental studies on the mechanical, magnetic and electrical aspects of the two systems have been followed up, but less on the optical properties.Therefore, the optical properties of Fe-B system and C-N system are studied by using the multibody perturbation theory and density functional theory under the first principle, respectively.The structure, band structure and density of state of TP10-FeB _ 4 I41 / acd-FeB _ 4 and oP12-FeB2 have been studied by GGA PBE method.The optical properties are analyzed by GW BSE method.The structure shows that the band gap of oP12-FeB2 is small, and the absorption coefficient appears obvious absorption peak in the visible region, which can be used as optical absorption material, while t P10-FeB4 and I41/acd-FeB4 occupy less orbit at the two ends of the band gap because of the wide gap.The absorption was strong in ultraviolet light, but very small in visible region.Eleven structures of C-N system are studied by using the GGA PBE method of density functional theory.The crystal structure parameters, electron transition mechanism, the origin of dielectric function peak and optical properties are analyzed in detail.All structures are compared by optical properties.Based on the optical characteristics of different structures and their mechanical properties, the potential applications of this kind of structural materials are preliminarily predicted.I2d-CN2 structure was selected to study Ti doping in C-N system.The structural parameters, electronic structure, optical properties and mechanical properties of Ti substitution N and Ti substitution C were analyzed and compared by different substitution methods and doping concentration.The optical properties are obviously changed due to the spin polarization phenomenon caused by the different number of electrons in the outer layer.The absorption coefficient indicates that the absorption of N element in the visible region is stronger than that of the substitution C element in the visible light region.Based on the mechanical and optical properties of these doped structures, we have determined the optimum doping concentrations.
【学位授予单位】：鲁东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O469

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