Spin-assisted covalent bond mechanism in charge-ordering perovskite oxides

First-principles density functional calculations on the metal-insulator transition (MIT) in perovskite CaFeO3 point to local ferromagnetic coupling as the microscopic origin for the electronic charge order transition. Our atomic, electronic, and magnetic structure analyses reveal that the MIT results from a spin-assisted covalent bonding mechanism between the O 2p and Fe 3d states with anisotropic Fe-O bonds and negligible intersite Fe-Fe charge transfer. We suggest that control of the lattice distortions, which mediate the covalent bond formation, in oxides containing late transition-metal row cations in high valence states provides a platform to tailor electronic transitions.