失配层结构Bi-Ca-Co-O体系的量子化学计算

Quantum Chemical Calculation of Bi-Ca-Co-O with Misfit-layer

采用密度泛函离散变分方法计算了[Bi_(1.68)Ca_2O_4]^(RS)[CoO_2]1.69的电子结构以及化学键,讨论了它们与热电性能之间的关系。从计算结果可以看出,Bi钴酸盐的电子结构有明显的半导体特征,在费米能级附近,Co 3d、Bi 6p和O 2p轨道在费米能级附近做主要贡献。在CoO_2层中,Co 3d和O 2p在费米能级到-4.5eV的范围内存在极强的杂化作用,而Bi-O/Bi-O层间的价键关系极弱。从原子净电荷及化学键级的计算结果看,Bi钴酸盐材料有明显的各向异性特征,而且在CoO_2层与中间层的层间仅存在Ca与O之间的弱结合。这些都将对体系的热电性能产生影响。

The relations among electronic structure,chemical bonds and thermoelectric properties of[Bi1.68-Ca2O4]RS[CoO2]1.69 with misfit-layer were analyzed by density function theory and discrete variational method.It could be found from calculation results that semiconductor characteristics of Bi misfit cobaltates were shown obviously,and that Co 3d,Bi 6p and O 2p atomic orbitals make main contribution to the highest valence band and the lowest conduction band.There was higher hybridization between Co 3dand O 2p in CoO2 layer in the range of Fermi level and-4.5eV;however,there was little valence bond interlayer Bi-O/Bi-O in middle layer from calculated covalent bonds and molecular orbital which gave a chance to modulate its crystal structure.The net charge of atoms and covalent bonds of Bi misfit cobaltates showed anisotropic property obviously and the week bonds of Ca and O between CoO2 layer and middle layer.These results will have influence on thermoelectric properties.