Achieving Ultrahigh Energy Storage Density of La and Ta Codoped AgNbO3 Ceramics by Optimizing the Field-Induced Phase Transitions

Energy storage capacitors are extensively used in pulsed power devices because of fast charge/discharge rates and high power density. However, the low energy storage density and efficiency of dielectric capacitors limit their further commercialization in modern energy storage applications. Lead-free AgNbO3-based antiferroelectric (AFE) ceramics are considered to be one of the most promising environmentally friendly materials for dielectric capacitors because of their characteristic double polarization–electric field hysteresis loops with small remanent polarization and large maximum polarization. An enhancement of these characteristics allows achieving a synergistic improvement of both the energy storage density and efficiency of the antiferroelectric materials. This work reports on a feasible codoping strategy enabling the preparation of AgNbO3-based ceramics with high energy storage performance. An introduction of La3+ and Ta5+ ions into the AgNbO3 perovskite lattice was found to increase the structural stability of the antiferroelectric phase at the expense of a reduction of local polar regions, resulting in the shifting of the electric field-induced antiferroelectric–ferroelectric phase transition toward higher fields. An ultrahigh recoverable energy storage density of 6.73 J/cm3 and high energy storage efficiency of 74.1% are obtained for the Ag0.94La0.02Nb0.8Ta0.2O3 ceramic subjected to a unipolar electric field of 540 kV/cm. These values represent the best energy performance in reported lead-free ceramics so far. Hence, the La3+/Ta5+ codoping has been shown to be a good route to improve the energy storage properties of AgNbO3 ceramics.