Energy Storage and Charge/Discharge Performance of Sm-Doped NBT-Based Lead-Free Ceramics

(Na 0.5 Bi 0.5 ) 0.75 Sr 0.25 TiO 3 – x Sm 2 O 3 ceramics (denoted as NBSTS x ) were obtained by the solid-state reaction method, and their crystal structure and morphological characteristics were characterized by X-ray diffractometer mapping (XRD) and scanning electron microscopy (SEM). The NBSTS x ceramics, when doped with a concentration of x = 0.03, demonstrated outstanding performance in terms of maximum recoverable energy storage density ( W rec ∼ 3.35 J/cm 3 ) and energy storage efficiency (η ∼ 84.8%). This ceramic exhibited the highest potential at an electric field strength of 210 kV/cm. Additionally, the thermal stability of NBSTS 0.03 ceramic remained constant within the temperature range of 30–90 °C, while their frequency stability covered the range of 10–1000 Hz. By analyzing the dielectric spectra of the material, we investigated the variation of the relative permittivity (ε r ) and the dielectric loss angle tangent (tan δ), and we probed the relaxation behavior by means of a modified Curie–Weiss law. The NBSTS x ceramic with a density of x = 0.03 exhibited a fast charge/discharge rate of 128 ns and a discharge energy density of 1.06 J/cm 3 . From the impedance spectra, the relaxation phenomena observed in the system could potentially be attributed to the migration of oxygen vacancies.