层状氧化物Ca_3Co_4O_9及掺铜体系的电子结构与化学键

Electronic structure and chemical bond in the layer cobalt oxide Ca_3Co_4O_9 and adding Cu element

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 relation among electronic structure,chemical bond and thermoelectric property of Ca_3Co_4O_9 and Cu-doped was studied using density function and discrete variation method（DFT-DVM）.The highest valence band（HVB） and the lowest conduction （LCB） are mainly contributed from Co3d,Cu3d and O2patomic orbitals.The property of semiconductor is shown from the gap between HVB and LCB.Furthermore,the gap of Cu-doped one is less than that of Ca_3Co_4O_9.The Ca-O weak bond between Ca_2CoO_3 and CoO_2 layer may induce the low thermal conductivity.Electronic structure and chemical bond of oxygen atom in Ca_2CoO_3 layer are shown anisotropy property obviously and the chemical bond along c axis is stronger than that of ab-plane,however,contribution of O2p atomic orbitals near Fermi energy along c axis is weaker than that of ab-plane.The covalent and ionic bonds of Cu-doped one are both weaker than those of Ca_3Co_4O_9.The thermoelectric property can be improved from adding Cu element into the system of Ca_3Co_4O_9.