High Td and large d33 achieved in Bi0.5Na0.5TiO3-based ceramics designed by a novel 2–2-like hamburger structure

There is an inherent trade-off between high piezoelectricity originated from structural instability and enhanced thermal stability derived from structural stability in Bi_0.5Na_0.5TiO₃ (BNT)-based piezoelectric ceramics. As a result, it is a significant challenge for simultaneously achieving both large piezoelectric coefficient (d₃₃) and high depolarization temperature (T_d). Herein, by designing the 2–2 hamburger-structured composites with different Ba^2 + concentration, a harmonious balance between depolarization temperature T_d (493 K) and piezoelectric coefficient d₃₃ (124 pC/N) is obtained in BNT-based ceramic composites. The large d₃₃ primarily originates from the coexistence of rhombohedral and tetragonal phases. The high T_d primarily benefits from the diffused ferroelectric-relaxor phase transition induced by the V-shaped Ba²⁺ diffusion gradient, localized electric field related to pores and residual stress. Consequently, our proposed strategy provides a novel perspective to boost both T_d and d₃₃ in BNT-based piezoceramics.