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The relation among electronic structure, chemical bond and thermoelectric property of Ca_3Co_4O_9 was studied using density function and discrete variation method (DFT-DVM). The gap between the highest valence band (HVB) and the lowest conduction band (LCB) shows a semiconducting property. Ca_3Co_4O_9 consists of CoO_2 and Ca_2CoO_3 two layers. The HVB and LCB near Fermi level are only mainly from O(2) 2p and Co(2) 3d in Ca_2CoO_3 layer. Therefore, the semiconducting or thermoelectric property of Ca_3Co_4O_9 should be mainly from Ca_2CoO_3 layer, but it seems to have no direct relation to the CoO_2 layer, which is consistent with that binary oxides hardly have a thermoelectric property, but trinary oxide compounds have quite a good thermoelectric property. The covalent and ionic bonds of Ca_2CoO_3 layer are both weaker than those of CoO_2 layer. Ca plays the role of connections between CoO_2 and Ca_2CoO_3 layers in Ca_3Co_4O_9, decrease the ionic and covalent bond strength, and improve the thermoelectric property.
The relation among electronic structure, chemical bond and thermoelectric property of Ca_3Co_4O_9 was studied using density function and discrete variation method (DFT-DVM). The gap between the highest valence band (HVB) and the lowest conduction band (LCB) shows a semiconducting property The HVB and LCB near Fermi level are mainly from O (2) 2p and Co (2) 3d in Ca_2CoO_3 layer. Thus, the semiconducting or thermoelectric property of Ca_3Co_4O_9 should be mainly from Ca_2CoO_3 layer, but it seems to have no direct relation to the CoO_2 layer, which is consistent with that of a binary oxide hardly have a thermoelectric property, but trinary oxide compounds have quite a good thermoelectric property. The covalent and ionic bonds of Ca_2CoO_3 layer are both weaker than those of CoO_2 layer. Ca plays the role of connections between CoO_2 and Ca_2CoO_3 layers in Ca_3Co_4O_9, decreasing the ionic and covalent bond strength, and improve the thermoelectric property.