Effect of Multiple Oxygen Vacancies on the Optical and Thermodynamic Properties of La0.75Sr0.25Co0.25Fe0.75O3-d Perovskite

The oxygen vacancy concentration of perovskites changes with the work condition in applications such as oxygen carriers and oxygen sensors. To explore the effect of multiple oxygen vacancies on the optical and thermodynamic properties, we perform first-principles calculations to investigate the formation of multiple oxygen vacancies in the paramagnetic La0.75Sr0.25Co0.25Fe0.75O3-delta. Our results show that the higher V-O concentration in La0.75Sr0.25Co0.25Fe0.75O3-delta occurs at the conditions of higher temperatures and lower oxygen partial pressures. The electrons liberated upon oxygen vacancy formation are partially localized on the nearby Fe/Co sites and partially delocalized through the lattice, with the result that the unoccupied Fe/Co states near the Fermi level decrease and the Fermi level shows an upward shift. From the results of optical absorption, the peaks from 250 to 600 nm are weakened and blue-shifted with an increase of oxygen vacancy concentration due to the decrease of empty Fe states and an upward shift of the Fermi level. The obvious change of optical absorption with oxygen vacancy concentration indicates that La0.75Sr0.25Co0.25Fe0.75O3-delta could be a good candidate for optical oxygen sensors in the visible spectrum.