Low-Field-Driven Superior Energy Storage Effect with Excellent Thermal Stability by Constructing Coexistent Glasses

In this work, we found that the defreezing coexistent glassy ferroelectric states hold significant potential for achieving superior energy storage performance, especially under low fields, by using phase field simulations and experimental approaches. A remarkable room-temperature energy recoverable storage density W_r exceeding 2.7 J/cm³ with a high efficiency η surpassing 80% under a low electric field of 170 kV/cm was obtained in the x = 6-12% compositions of x[Bi(Mg_2/3Nb_1/3)O₃]-(1-x)[0.94(Bi_0.5Na_0.5)TiO₃-0.06BaTiO₃-1%MnO₂] (BNBT-BMN) ceramics due to the combination of low P_r and high P_m of the coexistent ferroelectric glasses. Intriguingly, the superior W_r and η of the coexistent state of glasses can also be maintained in a wide temperature range of 293-430 K, indicating the excellent thermal stability of the energy storage behavior. Importantly, the W_r and η of this glass coexistent composition increase upon heating from room temperature to 360 K due to the defreezing process, leading to maximum W_r ∼ 2.9 J/cm³ with high efficiency η ∼ 90% of x = 10% at 360 K. When considering both energy storage behavior and thermal stability under low fields (<250 kV/cm), the BNBT-BMN ceramics outperform nearly all lead-free counterparts available today. Consequently, our work not only expands the research scope of ferroic glasses but also establishes a new paradigm for developing superior lead-free dielectrics suitable for high-temperature energy storage devices.