b 0 -Cu x V 2 O 5 nanowires exhibit reversible phase transitions from metallic to insulating states (i.e., a metal-insulator transition, MIT). Unlike in VO 2 where the MIT derives in part from a structural transition, the MIT in b 0 -Cu x V 2 O 5 is primarily an electronic phase transition. Here we show that the transition is underpinned by the diffusion of copper between two closely related sites, which drives polaron oscillation on the V 2 O 5 sublattice. This distinctive mechanism represents an intriguing approach to engineering energy-efficient MITs for neuromorphic computing applications.