Superior Energy Storage Performances under Moderate Electric Field Achieved in Bi_0.5K_0.5TiO₃-Based Ceramics via a Two-Step Optimization Design

Environmentally friendly lead-free relaxor ferroelectric ceramic capacitors with high energy density at moderate electric fields are critical for many pulse power systems. However, their moderate field energy storage property is usually restricted greatly by the limited polarization difference of the dielectric ceramic. In this work, a two-step optimization design strategy is adopted to optimize the energy storage performance of the Bi 0.5 K 0.5 TiO 3 (BKT) ceramic. In the first step, Ba 0.4 Sr 0.6 TiO 3 (BST) is added to reduce pores, boost polarization, and enhance the relaxor behavior. In the second step, CaTiO 3 (CT) is introduced to further enhance the breakdown strength and boost the polarization difference. Consequently, a large recoverable energy storage density ( W rec ∼ 5.78 J/cm 3 ) and a high energy efficiency (η ∼ 87.9%) are concurrently achieved in the BKT-BST-CT ceramic under a moderate electric field of 380 kV/cm. More importantly, the BKT-BST-CT ceramic exhibits a high utilization rate of the energy storage electric field with a gigantic W rec / E b of 0.015 J/kV·cm 2 . Furthermore, the ceramic has brilliant charge–discharge characteristics with a rapid discharge rate ( t 0.9 < 90 ns), a large current density (1151 A/cm 2 ), and a superpower density (143.9 MW/cm 3 ). The obtained findings indicate that the designed BKT-BST-CT specimen may be a prospective material for energy storage capacitor applications.