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本文采用基于密度泛函理论的第一性原理方法研究了未掺杂、A位掺杂与B位掺杂LaCrO3材料的电子结构，揭示了掺杂对材料电子结构影响的微观机理以及对导电性能的影响规律，为LaCrO3材料的开发利用做一些基础性的研究工作。首先对所需研究对象建立模型，优化几何结构，之后进行自洽计算得出能带结构、电子态密度分布、重叠布居和Mulliken电荷布居并进行分析。主要结论如下：（1）构建了无掺杂LaCrO3模型，研究了无掺杂情况下体系的电子结构。无掺杂LaCrO3为间接带隙半导体材料，费米能级附近的价带与导带由自旋为alpha态的电子能级构成；价带范围（-8eV-0eV）主要由Cr的3d态与O的2p态轨道成键构成；导带范围（0eV-6eV）是由La的5d、Cr的3d以及O的2p态轨道成键构成；La-O键为离子键，Cr-O键为共价键。（2）构建了三种不同Ca掺杂浓度的LaCrO3模型，研究了A位掺杂的性质。掺Ca后体系的晶胞体积变小， Ca掺杂使晶胞发生畸变；Ca掺杂后费米能级进入价带，材料变成p型掺杂半导体；随着Ca掺杂浓度的增加，价带顶与导带底的间隙逐渐缩小，材料的导电性增强，与文献实验结果吻合；由电子态密度分布图分析出Ca的掺入影响Cr原子3d轨道电子的分布状态，从电子态密度分布的角度验证了Zener的双重交换理论。（3）构建了三种不同Mn掺杂浓度的LaCrO3模型，研究了B位掺杂的性质。掺Mn后体系的晶胞体积变大，费米能级附近的能带仍然是由自旋为alpha态的电子能级构成；Mn掺杂后导带底与价带顶发生交叠，带隙消失，随着Mn掺杂浓度的增加，交叠程度加剧；费米能级附近的能带宽度随掺杂量的增加而变宽，电子的有效质量变小，容易受外场作用而获得加速度；Mn的掺入对La、Cr原子的电子转移影响不大，Mn主要与O之间发生电荷转移；Mn-O键的长度大于Cr-O键的长度，Cr-O键的共价性更强，La-O键仍为离子键。;In this thesis, the electronic structures of undoped, A-site doped and B-site doped LaCrO3 materials are studied by the first-principles method based on density functional theory. The micro-mechanism of the influence of doping on the electronic structure and the law of the influence on the conductivity of LaCrO3 materials are revealed. Some basic research work is done for the development and utilization of LaCrO3 materials.Firstly, the model of the research object is established and the geometric structure is optimized. Then, the band structure, electron density distribution, overlapping population and Mulliken charge population are calculated and analyzed by self-consistent calculation. The main conclusions are as follows: (1) LaCrO3 without doping is an indirect bandgap semiconductor material. The valence band and conduction band near Fermi level are composed of spin-alpha electrons. The valence band range (-8eV-0eV) is mainly composed of the 3d state of Cr and the 2p state of O. The conduction band range (0eV-6eV) is composed of the 5d, 3d and 2p state of La, 3d and O. The La-O bond is an ionic bond and the Cr-O bond is a covalent bond. (2) three different Ca doped LaCrO3 models were constructed, and the properties of A-site doping were studied. After adding Ca, the cell volume of the system decreases and Ca doping causes distortion of the cell. After doping Ca, Fermi energy enters valence band and the material becomes P doped semiconductor. With the increase of Ca doping concentration, the gap between the top of valence band and the bottom of conduction band decreases gradually, and the conductivity of the material increases, which is consistent with the experimental results in the literature. The influence of Ca doping on the distribution of 3d orbital electrons of Cr atom is analyzed from the electron density distribution diagram. Zener's double exchange theory is validated from the point of view of the distribution of electron density of states. (3) three different Mn doped LaCrO3 models were constructed, and the properties of B-site doping were studied. After doping Mn, the cell volume of the system becomes larger, and the energy band near the Fermi level is still composed of the electronic energy level with spin as alpha state. After Mn doping, the conduction band bottom overlaps with the valence band top, and the band gap disappears. With the increase of Mn doping concentration, the overlap degree increases. The bandwidth near the Fermi level broadens with the increase of doping content, and the effective mass of electrons decreases. The acceleration is easily obtained by the external field. The incorporation of Mn has little effect on the electron transfer of La and Cr atoms, and Mn mainly takes charge transfer with O. The length of the Mn-O bond is longer than the length of the Cr-O bond, and the covalent bond of the Cr-O bond is stronger. The La-O bond is still an ionic bond.
|白洋. 掺杂对铬酸镧电子结构影响的第一性原理研究[D]. 中国科学院大学,2018.|
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