Theoretical study of the optical and thermodynamic properties of LaxSr1-xCo1-yFeyO3-δ (x/y=0.25, 0.5, 0.75) perovskites

The performance of LaxSr1-xCo1-yFeyO3-delta perovskite systems in applications such as solid oxide fuel cells and catalysis is related to the proportion of substitution atoms. Using a density functional theory method, we investigate the doping effect on the electronic, optical, and thermodynamic properties of LaxSr1-xCo1-yFeyO3-delta (x/y = 0.25, 0.5, 0.75). Our results show that La doping introduces an empty state and pushes the Fermi level upwards. The doping Fe derived states locate away from the Fermi level as compared with Co states. From the results of optical absorption, the peak at 200-300 nm is enhanced and experiences a blue-shift with increasing La concentration. The corresponding peak at 400-700 nm also shows a blue-shift induced by both La and Fe doping, and it could be enhanced by Fe doping while being suppressed by La doping. And the peak above 1500 nm is enhanced by the cooperation of La and Fe doping. From thermodynamic calculations via an Ellingham diagram, it is found that the parent SrCoO3 is the most favorable composition for releasing O-2, with both La and Fe doping hampering the reduction reaction. Therefore, the optical and thermodynamic properties of LaxSr1-xCo1-yFeyO3-delta could be adjusted by special doping values.