Stress-modulated phase boundaries and ferroelectricity in NaNbO3: mechanical double-loop behavior near the P→R transition

As the demand for renewable energy continues to grow, the need for efficient energy storage systems becomes increasingly critical. Lead-free antiferroelectric NaNbO 3 has attracted considerable attention due to its promising polarization switching behavior under an applied electric field, offering significant potential for advanced energy storage applications. Although considerable efforts have been devoted to enhancing its energy storage density and efficiency, investigations into its mechanical properties remain limited, particularly under conditions that simulate realistic thermal environments. Here, by combining X-ray diffraction with in situ uniaxial stress Raman spectroscopy, we demonstrate that polycrystalline NaNbO 3 ceramics initially adopt a structure dominated by the antiferroelectric P phase, coexisting with a ferroelectric Q phase. The ferroelastic behavior is primarily governed by both ferroelastic domain switching and stress-induced irreversible AFE P→FE Q phase transitions, closely resembling the well-known irreversible electric field-induced AFE-to-FE transformation. Remarkably, at elevated temperatures, NaNbO 3 exhibits a distinctive double-loop-like hysteresis with mechanical constitutive characteristics that deviate from those of conventional ferroelectrics or antiferroelectrics. Permittivity variations with temperature under constant uniaxial stress reveal that this anomalous ferroelasticity may originate from stress-induced domain wall rotation and shifts in different ferroelastic phase transition. Analysis of the elevated-temperature mechanical constitutive behavior of polycrystalline NaNbO 3 ceramics provide mechanistic insights into ferroelectric and antiferroelectric materials under realistic conditions, offering reference for the design and practical application of antiferroelectrics.