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.