Atomic-scale insight into the oxygen ionic transport mechanisms in La2NiO4-based materials

The computer simulation studies employing both static lattice and molecular dynamics (MD) methods, were used to identify anion migration pathways, relevant energetic parameters and effects of the transition metal cation dopants on oxygen ion transport in La2Ni(M)O4+δ (M = Fe, Co, Cu) solid solutions, a family of promising oxide materials for fuel cell electrodes and dense ceramic membranes for oxygen separation. The factors related to different oxygen sublattices in the K2NiF4-type structure of La2Ni(M)O4+δ were appraised analyzing the MD data. The results show, in particular, that the incorporation of dopants having 3+ oxidation state leads to higher ionic charge-carrier concentration affecting the overall anion diffusivity, which is essentially determined by cooperative mechanisms involving oxygen interstitials and anions occupying regular apical sites in the layered lattices. However, these dopants tend to decrease anion mobility, both in the rock-salt and perovskite-like layers of the K2NiF4-type structure. The likely microscopic mechanisms of anion diffusion in oxygen-hyperstoichiometric La2Ni(M)O4+δ are determined.