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采用密度泛函离散变分方法计算了Sr位掺杂对Bi-Sr-Co-O的电子结构和化学键的影响,讨论了它们与热电性能之间的关系。计算结果表明,掺杂前后,两体系的电子结构表现出半导体特征。与未掺杂的相比,掺Ca体系的能隙变窄,Co 3d、O 2p和Bi 6p仍在费米能级附近在主要贡献,Ca 4s轨道贡献向费米能级移动。通过计算键级和分子波函数轨道可知,两体系的化学键在不同方向上均体现了明显的各向异性特征,在Bi-Sr钴酸盐体系中不同层间存在着多组弱结合,掺Ca后原子间相应的键级减弱。这些都将有利于改善材料的热电性能。
The influence of Sr doping on the electronic structure and chemical bond of Bi-Sr-Co-O was calculated by using density functional discrete variational method. The relationship between them and the thermoelectric properties was discussed. The calculated results show that the electronic structures of the two systems show the characteristics of semiconductors before and after doping. Compared with undoped, the bandgap of Ca-doped system becomes narrower and Co 3d, O 2p and Bi 6p are still the main contribution near the Fermi level, and the orbital of Ca 4s contributes to the Fermi level shift. By calculating the orbital and the molecular orbital, we can see that the chemical bonds of the two systems show obvious anisotropy in different directions. There are many groups of weak bonds between different layers in the Bi-Sr cobaltate system, Ca After the corresponding atomic bond between the weakened. These will help to improve the material’s thermoelectric properties.