层状结构钴酸盐热电材料的理论分析与研究

Research and Theoretical Analysis of Cobalt Oxide Thermoelectric Material with Layer Structure

采用密度泛函离散变分法计算了具有不同中间层的Na-Co-O和Ca-Co-O体系的电子结构和化学键。结果表明,在费米能级附近,两体系均有较强的峰值,且CoO2层中Co 3d和O 2p对价带和导带的贡献表现相似,Co3d在费米能级附近做主要贡献。通过对中间层比较分析可知,Na层中Na-Na之间存在金属键,而Ca2CoO3层则表现出明显的各向异性特征,这些也可从键级计算与波函数图形中看出。两体系的层间分别存在Na-O和Ca-O的弱结合,在NCO体系中还存在Na-Co的键性弱结合。由此可以看出,对两体系Na、Co和Ca的组分调节都将对材料的热学和电学性能产生影响。

Density function theory and discrete variation method （DFT-DVM） is applied to calculate electronic structure and chemical bonds of Na-Co-O system and Ca-Co-O system with different middle layer. The results include that higher peak value of two systems come out between the highest valence band （HVB） and the lowest conduction band （LCB）, and that the performance of Co 3d and O 2p atomic orbitals are similar in CoO2 layer~ especially, the contribution of Co 3d atomic orbitals play an important role near Fermi energy. By comparison with middle layer, it can be discovered that there is Na-Na metallic bond in Na layer, and that Ca2CoOa layer shows anisotropie property ob-viously, which can be found through calculated molecular orbitals and bond orders of two systems. Furthermore, Na-Co, Na-O and Ca-O are weak bond between interlayer of two systems. So component adjustment of Na, CO and Ca of these systems will have an influence on thermology and electricity property.