Redox‐Governed Phase Selection Enables Multimetal Perovskite Synthesis by Acidic Redox‐Assisted Precipitation

Synthesis of multinary perovskite oxides is often limited by unstable phase formation and uncontrolled metal incorporation. Acidic redox‐assisted precipitation (ARP) offers stoichiometric redox control but has historically produced spinel or amorphous oxides rather than ABO 3 phases. Here we show that introducing citric acid redirects ARP into a phase‐selective, perovskite‐forming pathway, enabling the synthesis of phase‐pure La–Co–Mn oxides. Phase selection arises from competition between Co 2+ –MnO 4 − oxidation and citric‐acid‐to‐MnO 4 − reduction, establishing a redox stoichiometric window and enabling reaction‐selective metal incorporation that yields an A:B ratio approaching 1:1. The final composition reflects composition selection rather than precursor replication, revealing a previously unrecognized dimension of redox‐governed phase selection in multimetal oxide synthesis.