A Strategy of Enhancing Polarization to Achieve Excellent Energy Storage Performance in Simple Bi_0.5K_0.5TiO₃-Based Relaxors

Dielectric energy storage capacitors are indispensable components in advanced electronic and electrical systems. Excellent performance requires the dielectric materials possessing low residual polarization (P_r), high breakdown strength (E_b), and large maximum polarization (P_m). The first two parameters can be typically achieved through chemical regulation, while the P_max is closely related to the matrix. Theoretical calculations demonstrate that a strong coupling of A-O bonds and a large lattice can enhance polarization, thus identifying the prototype Bi_0.5K_0.5TiO₃ as a favorable matrix. Here, ultrahigh energy density of 16.5 J/cm³ and high efficiency of 88.2 % are achieved in 0.76Bi_0.5K_0.5TiO₃-0.24Ca_0.5Sr_0.5HfO₃ binary system. This system exhibits the highest comprehensive performance among all reported Bi_0.5K_0.5TiO₃-based ceramics. The large perovskite framework facilitated by the large ionic radius of K⁺ enhances the local polarity of Bi−O and Ca−O, resulting in a large P_m of 57.4 μC/cm² under an ultrahigh E_b of 82 kV/mm. The highly disordered local polar clusters at the nanoscale lead to negligible P_r and high η. This work not only provides a unique design concept to enhance the comprehensive energy storage performance from the perspective of local structure, but also offers insight into the origin of high performance.