Quenching-induced polar state transformation and enhanced electromechanical response in BNT-Mn single crystals

Ultra-fast cooling at high temperatures provides a promising strategy for enhancing the thermal stability of (Bi_1/2Na_1/2)TiO₃-based (BNT) relaxor ferroelectrics, yet its role in tuning the polar state has been largely overlooked. In this work, we demonstrate that liquid nitrogen quenching (LNQ) can induce a transition from a predominantly ergodic relaxor (ER) to a long-range ferroelectric (FE) state in 0.5mol. % Mn-modified BNT single crystals. The LNQ-treated crystals exhibit a piezoelectric coefficient of 172 pC/N and a depolarization temperature of 170°C, representing enhancements of 7 times and 95%, over the as-grown (AG) crystals. This synergistic improvement in piezoelectric performance and thermal stability is associated with enhanced rhombohedral distortion (rhombohedral angle α: 89.857° for AG vs 89.701° for LNQ) and the ER-to-FE transition driven by LNQ. Local piezoelectric response and the thermal evolution of in situ piezoresponse force microscopy domain structure as well as electrical properties further confirm the improved ferroelectricity and thermal stability induced by liquid nitrogen quenching. These findings provide valuable insight into the tunability of polar states in BNT-based materials.