Origin of Metal–Insulator Transition in n-doped ABO₃Perovskite Metals

A subclass of ABO_x perovskites undergoes metal-to-insulator transitions (MITs) when n-doped either via oxygen vacancies concomitant with ordering, chemical substitution or strain. For example, the oxygen-rich perovskite SrCoO₃ is a ferromagnetic metal, while the oxygen-deficient brownmillerite SrCoO_2.5 is an anti-ferromagnetic insulator. The precise mechanism driving the MIT, and its relation to the electronic-structure of the metallic phase, remains unknown. Here we hypothesize that metallic ABO₃ that are more susceptible to a MIT via n-doping are self-hole doped negative charge transfer metals; n-doping fills these pre-existing holes and gives rise to an insulating state. Magnetism is a secondary effect that may or may not assist in the gap opening. Moreover, this tendency to remain self-hole doped determines a universal electronic response to modulations in stoichiometry/composition/pressure. In this work, we use ab-initio density functional theory (DFT), DFT+U, DFT+hybrid as well as many-body quantum Monte Carlo (QMC) calculations to shed light on the hypothesis, with comparison to experiments where possible.