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

Abstract 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 0.5 Bi 0.25 Na 0.25 )(Ti,Zr)O 3 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.