High energy-storage density under low electric field in lead-free relaxor ferroelectric film based on synergistic effect of multiple polar structures

Although dielectric energy-storage devices are frequently used in high voltage level, high voltage risk and large cost of insulation technology have increased the demand on the energy-storage devices at finite electric field strength. Here, we propose an approach on enhancing energy-storage density (W-rec) of dielectric materials under low electric field by utilizing the synergistic effect of multiple polar structures. An excellent W-rec of 40.8 J/cm(3) under only 1500 kV/cm is obtained in 0.5(Bi-0.5 Na-0.5)TiO3-0.5Bi(Zn0.5Zr0.5)O-3 (BNT-0.5BZZ) relaxor ferroelectric film, resulting in a large energy-storage coefficient that exceeds most of the dielectric materials. It is revealed that the addition of BZZ to BNT matrix induces the distortion of the octahedral [TiO6] in the lattice and establishes a coexistence structure of ferroelectric domains and polar nanoregions (PNRs), which enlarges the discrepancy between the maximum polarization and the remnant polarization. Besides, the BNT-0.5BZZ film shows strong fatigue endurance after 5 x 10(7) cycles and good thermal stability in a wide temperature range (25-145 degrees C). This work not only develops a promising lead-free candidate for low electric field electrostatic energy storage, but also, more importantly, opens up a new door to systematically design lead-free dielectrics for high-energy-storage applications at low electric field via microstructural engineering.