High energy storage capacity and relaxation ferroelectric characteristics of fine-grained Ba0.99Bi0.01TiO3@MnO core-shell nanoceramics

A novel core-shell structured Ba_0.99Bi_0.01TiO₃@xMnO (BBT@MnO) (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 mol%) relaxation ferroelectric ceramics were prepared by co-precipitation method. The structures, insulating, dielectric, and energy storage properties of the BBT@MnO ceramics were systematically investigated. According to TEM, the particles had a diameter of about 430 nm, high uniformity, and high dispersity. They were fabricated using a coating technique to simultaneously improve both the dielectric breakdown strength (BDS) and densification of the ceramics. The thickness of the MnO layers in the BBT@MnO particles averaged about 19 nm. Complex impedance testing of BBT@MnO ceramics revealed that only a one-grain boundary response existed for all ceramics, with the best insulating properties at x = 0.4 mol%. Furthermore, MnO coating increased lattice distortion and polarization intensity, altering the crystal structure and microstructure morphology while increasing energy storage density. The ceramics with 0.4 mol% MnO coating showed thin P-E hysteresis loops, with an optimal dielectric constant of 3610, a dielectric loss of 0.01, and the discharged energy density (J_d) of 0.26 J/cm³ and efficiency (η) of 76.5 %. The results showed that MnO coating is beneficial for reducing dielectric loss and improving insulation performance. This study provided valuable insights for the research of lead-free dielectric ceramic capacitors, and the BBT@MnO ceramics present good development prospects in high-power pulse energy storage systems.