(639d) Theoretical Investigation of the Electronic, Optical and Thermodynamic Properties of LaxSr1-XCoyFe1-YO3-? (x, y =0.0 ~ 1.0) Perovskites

The development of high temperature gas sensors for industrial applications is essential to improve energy efficiency and reduce toxic emissions. However, gas sensors operating at high temperatures encounter many challenging issues, such as thermal and long-term stability, sensitivity, reproducibility and selectivity. Sensing processes at such high temperatures are complicated and have not well understood. Hence, theoretical modeling could play a role to explore the sensing mechanisms and support experimental development of practical sensor devices. The perovskites in the form of ABO₃ (A=alkaline-earth metal or La, B=3d transition metal) are good candidates as high temperature sensor materials. In this study, the electronic, optical and thermodynamic properties of La_xSr_1-xCo_yFe_1-yO_3-δ (x, y = 0.0 - 1.0) are investigated using density functional theory calculations. The obtained results showed that pure SrMO₃ (M=Co, Fe) are metals, while LaMO₃ are insulators and all of them exhibit strong hybridization of the Fe/Co-3d and O-2p orbitals. By correlating the energy band structures with the peaks of the imaginary part of the dielectric function, we obtained that the origin of each electron excitation provides information about the active bands for the corresponding optical transitions observed in the experiment. By exploring the influence of O vacancy on their optical properties, we found that there are extra optical absorption peaks from vacancy-level transition for LaMO₃ insulators, however, the O vacancy has little influence on the optical properties of SrMO₃ metals. The optical absorption coefficients of LaMO₃ are very different for their high and low temperature phases. We also found that the optical absorption coefficients of SrMO₃ are influenced by the electronic correlation. The calculated thermodynamic properties versus temperatures are in good agreement with the available experimental data. Our results showed that the properties of pure LaMO₃ could be adjusted or enhanced for specific applications by chemical doping, hence, the doped La_xSr_1-xFe_yCo_1-yO₃ systems could possess improved performance and are under exploration.