Enhancement of piezoelectric performance in (Bi_1/2Na_1/2)TiO₃-based system through single-crystallization

(Bi_1/2Na_1/2)TiO₃-based ceramics are prominent candidates for lead-free piezoelectric applications; however, they are hampered by low piezoelectric coefficients (∼200 pC/N) and low depolarization temperatures (∼100 °C). Herein, we present a strategy for enhancing the comprehensive piezoelectric performance of these ceramics through single-crystallization. High-quality 0.85(Bi_1/2Na_1/2)TiO₃-0.11(Bi_1/2K_1/2)TiO₃-0.04BaTiO₃ (BNT-11BKT-4BT) single crystals were synthesized using a flux growth method. These crystals exhibit significantly enhanced piezoelectric coefficients (∼360 pC/N) and elevated depolarization temperatures (∼220 °C) compared to random ceramics with equivalent composition. The observed increase in depolarization temperature by 100 °C in single crystals, attributed to an elevated c/a ratio (1.014 versus 1.005 in random ceramics). Notably, the piezoelectric coefficient surpasses 1000 pC/N at 210 °C, a phenomenon linked to the flattening of the free energy near the tetragonal-pseudocubic phase transition point. Furthermore, the polarization and electrostrain demonstrate remarkable temperature stability, owing to the improved depolarization temperature. This study elucidates a pathway towards advancing the comprehensive piezoelectric performance of (Bi_1/2Na_1/2)TiO₃-based materials, providing valuable insights for future research and development in the field.