Critical role of interfacial polarization suppression in enhancing breakdown strength and energy storage performance of NBT-based dielectric ceramics.

Abstract

Lead-free dielectric ceramics hold significant promise in the field of energy storage materials. To achieve optimal energy storage performance (ESP), it is essential to reach a large difference (∆P) between the maximum polarization (Pmax) and remnant polarization (Pr), while also ensuring a high breakdown strength (Eb). A conventional approach to obtaining a large ∆P involves selecting ferroelectric materials with strong polarization (such as Na0.5Bi0.5TiO3, NBT), and introducing a secondary component to induce relaxor behavior. Recent studies have shown that matching the resistances of grains and grain boundaries to suppress interfacial polarization, thereby eliminating local charge accumulation, is beneficial for enhancing Eb. In this work, we fabricated a series of (1-x)Na0.5Bi0.5TiO3-xCa0.7Nd0.2TiO3 (NBT-xCNT) ceramics. It is revealed that the incorporation of non-polar dielectric CNT not only enhances the relaxor behavior, but also suppresses the interfacial polarization, effectively boosting the Eb. In particular, the NBT-0.24CNT sample exhibits the weakest interfacial polarization and the highest Eb, resulting in a large ΔP of 50.3 μC/cm3, a high recoverable energy storage density Wrec of 9.02 J/cm3, and a large Wrec/E value of 0.018 J·kV-1·cm-2 at 500 kV/cm. Notably, the NBT-0.24CNT sample shows the lowest resistance among all prepared samples, as evidenced by complex impedance spectra and leakage current tests, suggesting that the interfacial polarization suppression for enhancing Eb is still effective despite the typically unfavorable effect of reduced insulation. These findings distinctively demonstrate the critical role of interfacial polarization suppression in enhancing Eb and ESP, offering useful insights for the development of high-performance energy storage ceramics.