Local Polymorphic Nanoclusters Enhanced Capacitive Energy Storage in Lead-Free Superparaelectrics

Lead-free dielectric capacitors with a high power density and fast discharge speed are the core components for next-generation pulse power systems. However, the low energy storage density and efficiency limit the development of devices toward miniaturization and low power consumption. In this work, guided by phase-field simulation, we introduce low-tolerance-factor components composed of multielements to significantly enhance random fields for regulating the local structure, resulting in the formation of local polymorphic nanoclusters with ultrasmall sizes of 1-2 nm, which can be identified by atomic-resolution scanning transmission electron microscopy. Through controlling this distinctive polarization configuration, high polarization fluctuations, low hysteresis, and delayed polarization saturation behavior under ultrahigh electric fields can be achieved, which contribute to an ultrahigh energy density of 11.6 J cm^-3 with an exceptional efficiency of 92% in BaTiO₃-based lead-free superparaelectrics. This work demonstrates that the strategy of local polymorphic nanoclusters is effective in developing advanced dielectric capacitors with excellent energy storage properties.