Synergistic phase and octahedral tilt boundaries enable record BNT piezoelectricity

Bi_1/2Na_1/2TiO₃ (BNT) ceramics are a prototypical class of lead-free piezoelectric materials, widely investigated for their large spontaneous polarization and substantial electrostrain. However, their piezoelectric coefficients remain lower than those of conventional PZT ceramics, limiting practical applications. Although single crystals can deliver superior performance compared with polycrystalline ceramics, growth of high-quality BNT single crystals is hindered by multiple technical challenges, so studies focused on single crystals remain relatively scarce.

Here, we propose a synergistic control strategy that combines T–PC phase-boundary engineering with modulation of oxygen-octahedral tilt boundaries, and we apply this approach to grow high-quality, Nb-modified Bi_1/2Na_1/2TiO₃-Bi_1/2K_1/2TiO₃–BaTiO₃ single crystals using a flux growth method. The resulting single crystals exhibit an exceptional piezoelectric coefficient d₃₃ of 662 pC/N, representing the highest comprehensive performance reported to date in the BNT family. In addition, we reveal a distinctive electric-field-induced strain behavior of BNT-based single crystals near the depolarization temperature.

This work not only provides a practical route for the development of high-performance, lead-free piezoelectric single crystals for next-generation sensors and actuators but also deepens the understanding of structure–property relationships in piezoelectric materials. The work entitled “Tetragonal-pseudocubic phase boundaries and octahedral order-disorder tilting transitions facilitate high piezoelectric performance in Bi_1/2Na_1/2TiO₃-based single crystals” was published in Advanced Powder Materials (Available online on 26 September 2025).