Electronic Structure and Thermoelectric Property of Misfit Layered Cobaltite and Doped Series

摘要

The relations between electronic structure, chemical bond and thermoelectric property of misfit layered cobaltite of Ca_3Co_4O_9 and 3d transitional metal (Ti, Cr, Mn, Fe and Cu) doped series are studied using density function and discrete variation method (DET-DVM). Ca_3Co_4O_9 consists of two layers of CoO_2 and Ca_2CoO_3- The highest valence band (HVB) and the lowest conduction band (LCB) near Fermi level are only mainly from O 2p and Co 3d in Ca_2CoO_3 layer. Therefore, the semiconductor, 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 thermoelectric property, but trinary oxide compounds have quite good thermoelectric property. The variation of electronic structure, chemical bond strength and thermoelectric property of doping series is discussed. The improvement of thermoelectric property of Cu-doped Ca_3Co_4O_9 is the most obvious.