Energy storage performance of Na_0.5Bi_0.5TiO₃ based lead-free ferroelectric ceramics prepared via non-uniform phase structure modification and rolling process

With the rapid growth of electronic devices towards to miniaturization and integration, the Pb-free ceramic materials with excellent recoverable energy storage density and efficiency are extremely required for the real application of pulse power capacitors. Moreover, it is also a huge challenge to sustain excellent energy storage performance in a dynamic temperature. The paper proposed a design strategy for building the co-existence of polymorphic PNRs through phase structure control. Based on the strategy, (1-x)(0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃)-xBiMg_2/3Nb_1/3O₃ ((BNT-BT)-xBMN) solid-solution was engineered and synthesized to achieve co-existence of tetragonal and rhombohedral phase PNRs in the perovskite structure. The pinch phenomenon of the P-E loops is linked with the phase transition caused by the electrical field. High polarization with limited hysteresis has been achieved, taking advantage of ample hybridization between O^2– 2p and Bi³⁺ 6p orbitals for polarization and increased structural disorder caused by composition modification. With the further enhancement of the electrical breakdown strength by the rolling process, an ultra-high energy density of 6.3 J/cm³, an improved energy efficiency of 79.6% and an excellent temperature stability (W_rec > 5.03 J/cm³, η > 82%, and a small variation of W_rec (less than 10%) in the temperature range of 30 to 170 °C) were achieved. The current work shows that this strategy is very important and successful in the design of high-performance Pb-free dielectric capacitors for real applications in the future.