Enhanced energy storage performance and phase stability in Sm-modified 0.90NaNbO₃–0.10BiFeO₃ ceramics

NaNbO₃ is a promising, emerging lead-free antiferroelectric (AFE) ceramic due to its high bandgap and low density. However, irreversible phase transitions often lead to significant hysteresis, resulting in an unfavorable trade-off between recoverable energy density (U_rec) and energy efficiency (η). Herein, a composition-design route that balances polarizability, tolerance factor, and phase structure is proposed to stabilize a relaxor antiferroelectric R phase and enhance energy storage. First, BiFeO₃ is optimized in NaNbO₃ to obtain 0.90NaNbO₃–0.10BiFeO₃ with linear-like P-E loops but limited breakdown strength due to volatile Bi/Na-induced oxygen vacancies. Then, partial substitution of Bi3+ with Sm3+ improves electrostatic/structural stability via unit-cell contraction and stronger A-O bonding, suppressing vacancies and increasing insulation. The optimal composition, 0.90NaNbO₃-0.10Bi_0.8Sm_0.2FeO₃, exhibits an excellent U_rec of 6.6 J cm−3 and an η of 80% at 500 kV cm−1, with good thermal stability from 25 °C to 125 °C and fatigue endurance up to 106 cycles. Therefore, this ceramic with a thoroughly optimized Bi3+/Sm3+ ratio is a potential candidate for practical energy storage applications.