A Strategy of Enhancing Polarization to Achieve Excellent Energy Storage Performance in Simple Bi0.5K0.5TiO3‐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 (Pr), high breakdown strength (Eb), and large maximum polarization (Pm). The first two parameters can be typically achieved through chemical regulation, while the Pmax 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 Bi0.5K0.5TiO3 as a favorable matrix. Here, ultrahigh energy density of 16.5 J/cm3 and high efficiency of 88.2% are achieved in 0.76Bi0.5K0.5TiO3‐0.24Ca0.5Sr0.5HfO3 binary system. This system exhibits the highest comprehensive performance among all reported Bi0.5K0.5TiO3‐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 Pm of 57.4 µC/cm2 under an ultrahigh Eb of 82 kV/mm. The highly disordered local polar clusters at the nanoscale lead to negligible Pr 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.