Influence of atomic configuration on electronic and magnetic properties of complex Ruddlesden-Popper oxides La_2−xSr_xCo_1/2Fe_1/2O₄

Ruddlesden-Popper (RP) transition-metal oxides belong to a versatile class of functional materials whose electronic properties can be tuned by varying chemical composition in a wide range. However, the relation between chemical composition and electronic properties of multi-metal RP oxides, in particular taking into account different distributions of metal ions in the lattice, has not been investigated systematically so far. In this work, we use density-functional theory (DFT) to explore the compositional dependence of electronic, magnetic, and structural properties of La \(_{2-x}\) $2-x$ Sr \(_x\) $x$ Co \(_{1/2}\) $1/2$ Fe \(_{1/2}\) $1/2$ O \(_4\) $4$ oxide series for x = 0, 1, 2. To account for localized nature of transition-metal d-orbitals, self-consistent DFT+U approach Agapito-Curtarolo-Buongiorno-Nardelli (ACBN0) is employed. We show that widely used electronic-structure-based descriptors of oxygen-defect formation energies, oxygen transport, and catalytic activity strongly depend on the distribution of transition metal ions. Nevertheless, the distribution-averaged and ground-state descriptor values for La \(_{2-x}\) $2-x$ Sr \(_x\) $x$ Co \(_{1/2}\) $1/2$ Fe \(_{1/2}\) $1/2$ O \(_4\) $4$ are found to depend monotonically on the composition x. In addition, we showed that in complex systems such as multi-metal Ruddlesden-Popper phases, Hubbard U values for the same species vary significantly between crystallographically non-equivalent sites.