Oxygen migration performance of LaFeO₃ perovskite-type oxygen carriers with Sr doping

A perovskite-type metal oxide with the formula of ABO₃ exhibits excellent redox reaction properties for the chemical looping process, where A is usually an alkaline earth metal and B is a transition metal. The oxygen transfer property plays an important role in the performance of oxygen carriers. In this study, the difference in oxygen vacancy formation energy and oxygen migration barrier between the surface and the bulk in the LaFeO₃ (ABO₃ type) perovskite is investigated via density functional theory (DFT). The effect of Sr doping on the A-site is considered. The results show that the covalency of the interaction between Fe and O at the surface is higher than that in the bulk, and the Sr doping on the A-site enhances this covalency, leading to a lower oxygen vacancy formation energy. The oxygen migration barrier is also different with the distance from the surface. A smaller deviation of the surrounding lattice atoms from their original place in the crystal at a deeper layer leads to a higher oxygen migration energy. Meanwhile, Sr doping increases the lattice constant, leading to larger migration space thus lowering the migration barrier. In addition, Sr doping can weaken the difference in the oxygen migration barrier between near the surface and in the bulk.