Stabilization mechanism of antiferroelectric Pnma phase and low-field reversible phase transition in sodium niobate-based ceramics

The stabilization mechanism of antiferroelectric (AFE) phases in sodium niobate ceramics remains unclear, leading to irreversible AFE–ferroelectric (FE) phase transitions and requiring a high operating E-field, which significantly limits the utilization of AFE properties. In this work, leveraging insights from density functional theory calculations, we design and fabricate xBi_2/3SnO₃-(1-x)NaNbO₃ ceramics, overcoming these limitations by achieving both a reversible AFE–FE phase transition and a low operating field (< 200 kV×cm^-1). Notably, the optimized composition exhibits an exceptionally low remanent polarization compared to conventional AFE systems. Structural analysis reveals a three-stage phase evolution with increasing x: FE Q + AFE P phases (x < 0.02) ®pure AFE P phase (x = 0.02) ®coexistence of AFE P + AFE R phases (0.02 < x < 0.08). The AFE P phase is characterized by a 4-layer multicell structure (~1.65 nm), periodically disrupted by 6-layer antiphase boundaries (APBs, ~2.44 nm), which are associated with dislocation formation and a large energy difference between P and Q phases (7.20 meV×f.u.^-1). These features likely contribute to reduced domain size and lower field-induced AFE→FE transition. Furthermore, the stabilization of the AFE R phase is primarily caused by a reduction in the distortion index (from 0.047 to 0.003) and enhanced covalency in A-O and B-O bonds. This study provides new insights and theoretical guidance for developing low-field-driven reversible phase transitions in AFEs.