Giant Energy‐Storage in Pb‐Free Relaxor Ferroelectrics via Atomic‐level Design

Perovskite-structured relaxor ferroelectrics have been extensively studied as dielectric energy-storage capacitors, with applications across various electronics and electrical power systems. However, substantial improvements in energy-density are typically hindered by early polarization saturation and a rapid decline in polarizability under high-fields. To address this challenge, an atomic-level design strategy is presented that integrates framework, ferroelectric-active, rattling ions at A-site and insulating ions at B-site to induce a cooperative local polarization enhancement and rattling effects. Large-scale simulations and local structure analysis based on neutron total scattering reveal that large-sized framework ions enable local polarization enhancement of small ferroelectric-active and rattling ions through size differences. Rattling ions, endowed with an expanded displacement space, heighten field-driven polar extension, thereby slowing the reduction of polarizability under high-fields. Guided by this strategy, (Ba_0.5Bi_0.25Na_0.25)(Ti,Zr)O₃ system is elaborately designed, which exhibits favorable polarization behavior featured with deferred polarization saturation and record-high polarizability under an ultrahigh breakdown field. Consequently, the optimal composition demonstrates a giant energy density of 24.3 J cm^-3 with a high efficiency of 92.4%, outperforming current bulk ceramic capacitors. The work establishes a universal design paradigm for relaxor ferroelectrics toward next-generation dielectric capacitors, and provides a theoretical framework for the chemical design of function-orientated complex ferroelectrics.