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采用离散变分密度泛函方法计算了层状氧化物Ca_3Co_4O_9及掺铜体系,讨论了电子结构、化学键等与热电性能之间的关系。结果表明,层状氧化物的价带和导带主要由Co3d、Cu3d和O2p原子轨道贡献,能隙宽度表现出了半导体电子结构特征,且掺铜体系的能隙变窄。CoO_2层和Ca_2CoO_3层之间Ca-O的弱结合导致材料具有低的热导率。Ca_2CoO_3层O原子的化学键和电子结构都表现出明显的各向异性特征,在平行于c轴方向上离子键和共价键较强,且在该方向上O2p原子轨道对费米能级附近的贡献比ab面方向弱。掺铜后体系的化学键都减弱,这将对材料的热电性能产生影响。
The layered oxide Ca_3Co_4O_9 and the copper-doped system were calculated by the discrete variation density functional theory. The relationship between the electronic structure, chemical bond and the thermoelectric properties was discussed. The results show that the valence band and conduction band of the layered oxide are mainly contributed by the orbital of Co3d, Cu3d and O2p, the energy gap width shows the electronic structure of the semiconductor, and the energy gap of the Cu-doped system is narrowed. The weak binding of Ca-O between the CoO 2 layer and the Ca 2 CoO 3 layer results in the material having low thermal conductivity. The chemical bond and electronic structure of the O atom in Ca_2CoO_3 layer show obvious anisotropy, strong ionic bond and covalent bond in the direction parallel to the c axis, and in this direction, The contribution is weaker than the direction of ab. After the copper-doped system, the chemical bonds are weakened, which will affect the thermoelectric properties of the material.