Dielectric capacitors with high energy storage density (W_rec) and efficiency (η) are in great demand for high/pulsed power electronic systems, but the state-of-the-art lead-free dielectric materials are facing the challenge of increasing one parameter at the cost of the other. Herein, we report that high W_rec of 6.3 J cm^-3 with η of 90% can be simultaneously achieved by constructing a room temperature M2–M3 phase boundary in (1-x)AgNbO₃-xAgTaO₃ solid solution system. The designed material exhibits high energy storage stability over a wide temperature range of 20–150 °C and excellent cycling reliability up to 10⁶ cycles. All these merits achieved in the studied solid solution are attributed to the unique relaxor antiferroelectric features relevant to the local structure heterogeneity and antiferroelectric ordering, being confirmed by scanning transmission electron microscopy and synchrotron X-ray diffraction. This work provides a good paradigm for developing new lead-free dielectrics for high-power energy storage applications.

Aliovalent A-site engineering enables superior energy storage density in AgNbO₃ lead-free antiferroelectric ceramics.

High energy density was achieved by designing a AgNbO ₃ based lead-free system.

An ultrahigh energy storage density up to 4.87 J cm ⁻³ was achieved in Sm/Ta co-doped AgNbO ₃ ceramics, by decreasing the cation displacement and [Nb/TaO ₆ ] octahedral tilting angle.

Antiferroelectrics (AFEs) are promising candidates in energy-storage capacitors, electrocaloric solid-cooling, and displacement transducers. As an actively studied lead-free antiferroelectric (AFE) material, NaNbO₃ has long suffered from its ferroelectric (FE)-like polarization-electric field (P-E) hysteresis loops with high remnant polarization and large hysteresis. Guided by theoretical calculations, a new strategy of reducing the oxygen octahedral tilting angle is proposed to stabilize the AFE P phase (Space group Pbma) of NaNbO₃. To validate this, we judiciously introduced CaHfO₃ with a low Goldschmidt tolerance factor and AgNbO₃ with a low electronegativity difference into NaNbO₃, the decreased cation displacements and [BO₆] octahedral tilting angles were confirmed by Synchrotron X-ray powder diffraction and aberration-corrected scanning transmission electron microscopy. Of particular importance is that the 0.75NaNbO₃−0.20AgNbO₃−0.05CaHfO₃ ceramic exhibits highly reversible phase transition between the AFE and FE states, showing well-defined double P-E loops and sprout-shaped strain-electric field curves with reduced hysteresis, low remnant polarization, high AFE-FE phase transition field, and zero negative strain. Our work provides a new strategy for designing NaNbO₃-based AFE material with well-defined double P-E loops, which can also be extended to discover a variety of new lead-free AFEs.