The understanding of large electromechanical strain under low electric field in lead-free BNT-based relaxor

The abnormally large strain properties in (Bi, Na)TiO₃ (BNT)-based ceramics have been intensively investigated for nearly two decades. However, it is still a serious challenge that the threshold electric field for triggering large strain is excessively high, obstructing them toward practical applications. To overcome this issue, this study investigated that large strain properties under a low electric field can be realized by the synthesis of a ternary system with co-modifying BiAlO₃ (BA) and SrTiO₃ (ST) in BNT-based ceramics. Consequentially, a high S_max/E_max value of 850 pm/V was obtained in BNT-BA-24ST ceramics under a low electric field of 2 kV/mm. it was successfully suggested that the coexisting static PNRs in the ergodic relaxor state are responsible for changing the internal free energy (ΔE) of BNT-BA-24ST ceramics. This leads to a significant reduction of the threshold electric field to induce phase transition from ER to ferroelectrics, resulting in the realization of large strain under a low electric field.