Medium electric field-induced ultrahigh polarization response and boosted energy-storage characteristics in BNT-based relaxor ferroelectric polycrystalline ceramics

Lead-free dielectric ceramics with a high recoverable energy-storage density (W_rec) and improved efficiency (η) are crucial for the development of pulse power capacitor devices. Although W_rec has been constantly improving, mainly via an increased breakdown electric field strength (E_b), a large driving electric field (>500 kV/cm) increases security risks and consequently increases insulating technology costs. In this work, we present a new (Bi_0.5Na_0.5)TiO₃ (BNT)-based relaxor ferroelectric system, (1−x)(0.75Bi_0.5Na_0.4K_0.1TiO₃-0.25SrTiO₃)-xBi(Mg_0.5Ti_0.5)O₃ (BS-xBMT), with x ranging from 0.05 to 0.20. BMT disrupts both the A- and B-site long-range ferroelectric order of the ABO₃ perovskite-structured BS matrix, induces polar nanoregions, and simultaneously increases W_rec and η. Aided by the viscous polymer process, the E_b with x = 0.15 increased to 270 kV/cm, and a maximum polarization (P_m) of 62 μC/cm² was attained. A boosted W_rec of 4.82 J/cm³ and a high η of 84.9% were simultaneously obtained, together with good temperature stability from 30 to 140 °C. These results show that BNT-based dielectric ceramics with superior energy-storage properties can be obtained under a medium electric field.