Ultrahigh piezoelectricity by polaron-defect complexes

Materials capable of delivering giant and rapid piezoelectric responses at kilohertz frequencies are pivotal for advanced electromechanical technologies. However, their development has been constrained by a long-standing magnitude-speed trade-off: Ferroelectrics with intrinsic electric dipoles offer fast response but limited polarization, whereas ionic defect motion generates highly polarizable defect dipoles but responds slowly, limiting kilohertz-rate applications. We overcame this fundamental limitation by devising 8 mole % K-doped AgNbO₃ (Ag_0.92K_0.08NbO₃) thin films engineered to host dynamically reconfigurable polaron-defect complexes through electro-elastic interactions between small electron polarons and lattice defects. Field-driven multi-unit-cell polaron hopping reconfigures these complexes, producing giant defect polarization, and orders-of-magnitude faster kinetics of polaron hopping (versus ionic migration) enables their rapid response. This synergy leads to an unprecedented field-induced effective piezoelectric coefficient of ~7170 picometers per volt with ~6.2% strain at kilohertz frequencies in engineered silver niobate-based films.