Grain size modulated (Na_0.5Bi_0.5)_0.65Sr_0.35TiO₃-based ceramics with enhanced energy storage properties

Ferroelectric ceramics, as a potential candidate for high-power energy storage capacitors, lies in their excellent recoverable energy storage density (W_rec) and outstanding efficiency (η) in practical applications. Herein, a new type of lead-free ceramics (1-x)(Na_0.5Bi_0.5)_0.65Sr_0.35TiO₃-xBiMg_0.5Sn_0.5O₃ or (1-x)NBST-xBMS was prepared with the aim of enhancing the breakdown strength (E_b) and reducing the energy storage loss through grain refinement. It was found that E_b of 0.9NBST-0.1BMS reaches 405 kV/cm due to the reduction in the grain size of ceramic and thus the extremely high ratio of grain boundary resistance to grain resistance. Besides, a remarkable energy-storage performance was obtained, that is, W_rec and η are ∼ 6.68 J/cm³ and 89.1% at 405 kV/cm, respectively, along with excellent stability in terms of frequency, temperature, and fatigue endurance. The outstanding energy-storage performance is resulted from modulating the grain size via doping the moderate content of Bi³⁺ and Mg²⁺/Sn⁴⁺, which is beneficial to increase the breakdown field by increasing resistivity under high electric field while increasing the grain boundary activation energy and promote the formation of a relaxor state at the same time. More importantly, energy storage potential (defined as W_rec/E_b) is up to 0.01649 μC/cm², being the highest value reported so far for BNT-based ceramics in energy-storage application. Our results pave the way for practical applications of NBST-based ferroelectric capacitors with excellent energy storage performance.