Electronic structure of iron-doped misfit-layered calcium cobaltite

摘要

The electronic structures of the undoped and Fe-doped misfit-layered calcium cobaltite are calculated using the first-principles calculations under DFT + U scheme. The calculated density of states (DOS) of the undoped sample is in a good agreement with the past theoretical calculation and experiments. The Fermi level falls at nearly the top of the valence band of the CoO2 sublattice. The obtained magnetization could also very well explain the previous experiments. With Fe doping, two obvious changes in the DOS can be observed. Firstly, the Fermi energy has shifted to the higher level value and intercepted at the edge of the valence band where the slope is maximum. This characteristic enhances the thermopower of the system. The second change is the additional states similar to 0.1 eV above the Fermi level coming from the states of Fe atoms. These states are interpreted as a source of charge reservoir providing holes for electrical conduction in the CoO2 layer. The electronic structures of the Fe-doped case show very good agreement with the previous thermoelectric measurements. The thermopower, calculated using Boltzmann transport theory, is significantly enhanced in the Fe-doped system compared to the undoped one. (C) 2015 Elsevier B.V. All rights reserved.