Well-defined double hysteresis loop in NaNbO₃ antiferroelectrics

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.