An Intragranular Segregation Structure Enables an Excellent Energy Storage Performance in Composite Dielectrics through Delayed Saturation Polarization

An electrostatic capacitor for energy storage is an important basic component of pulse power electronics. The electrical breakdown strength (E_b) of normal ferroelectrics is low, which limits their application in dielectric energy storage. Constructing a 0-3-type composite dielectric, that is, introducing an insulating metallic oxide into the ferroelectric matrix, can greatly enhance E_b. Unfortunately, an intergranular secondary phase typically forms that causes large attenuation of the dielectric constant, which leads to limited improvement of energy storage performance. In this work, a composite ceramic with an intragranular segregation structure was intentionally designed using the BaTiO₃-BaZrO₃-CaTiO₃ (BCZT) system as an example. Compared with those of a BCZT solid solution without a secondary phase and a BCZT composite with a grain-boundary secondary phase, the rationally designed BCZT composite with an intragranular secondary phase delivered a large recoverable energy density of 5.86 J/cm³ and high efficiency of 86.7% at a moderate electric field of 550 kV/cm. Such performance was achieved because the intragranular segregation structure displayed delayed saturation polarization with a high E_b. This microstructural engineering strategy is generally applicable to optimize composite dielectrics to meet the demands of high-performance energy storage capacitors.