Frustrated polar slush-like state leads to advanced stability and high energy storage in NaNbO₃-based ceramics

Dielectric capacitors are extensively utilized in electronic and power systems due to their high operating voltage, superior power density, and rapid charge-discharge capability. Nevertheless, simultaneously attaining large recoverable energy density (W_rec) and high efficiency (η) together with robust thermal stability remains a persistent challenge. Here, guided by the phase field simulations, we introduce a frustrated polar slush-like strategy that disrupts nanoscale domains within the polar matrix into a highly disordered polarization state, accompanied by randomly distributed oxygen octahedral tilts with smaller tilt angles embedded within an ordered octahedral-tilt matrix possessing larger tilt angles, thereby effectively suppressing hysteresis loss by reducing domain-switching barriers and enhancing breakdown strength through grain refinement. A high W_rec of 8.52 J·cm⁻³ and ultra-high η of 96.61%, along with excellent temperature stability with a W_rec of 5.08 J·cm⁻³ and η of 95.31% at 160 °C, have been simultaneously achieved in NaNbO₃-based ceramic capacitors. This work delineates a viable route toward the rational design of dielectric capacitors that sustain high performance under elevated-temperature conditions.