First-principles study of La2CoMnO6: a promising cathode material for intermediate-temperature solid oxide fuel cells due to intrinsic Co-Mn cation disorder

La2CoMnO6 has attracted intensive research interest because of its prospect for novel technological applications and rich fundamental physics. And, due to the similar radii size as well as small covalent difference (as large as 2) between Co and Mn, cation disorder should be intrinsic within this perovskite. We performed comprehensive first-principles calculations on both La2CoMnO6 (LCMO) and LCMO with Co-Mn-Mn-Co antisite defects (AD:LCMO), focusing on the formation of bulk oxygen vacancies, which plays a key role in oxygen ion diffusion process in solid oxide fuel cell (SOFC) electrodes. First, it is found that the covalent states are 2 and +4 for Co and Mn at their regular sites while they are both prone to be +3 in the antisites. The formation energies for oxygen vacancies are predicted to follow the trend Co2+-O-Mn4+ > Co2+-O-Co3+ > Mn3+-O-Mn4+, and the underlying microscopic mechanism is attributed to the more electron delocalization between mixed-covalent transition metals (Co2+-O-Co3+ and Mn3+-O-Mn4+), which is beneficial to diminish the electronic repulsion and help to stabilize the vacancy. Therefore, we could conclude that oxygen ionic conductivity should be enhanced in the compounds with higher degree of cation disorder. Our results indicate that AD:LCMO should be a promising intermediate-temperature solid oxide fuel cell cathode material.