Pulsed power systems require high-performance capacitors with high energy storage density. In this work, (1 − x)BaTiO3-xBi(Mg1/2Sn1/2)O3 ferroelectric ceramics were synthesized in a solid-state solution. The sample of x = 0.12 (0.88BT-0.12BMS) has excellent energy storage density, wide temperature, and wide frequency stability. The excellent energy density of 4.87 J/cm3 at 315 kV/cm and the energy efficiency of 72% at room temperature for 0.88BT-0.12BMS ceramics were achieved. Furthermore, the 0.88BT-0.12BMS ceramics demonstrated well temperature stabilities in the range of 20–100 °C and very good frequency stability in the range of 1–100 Hz. Through pulsed charging–discharging testing, the current density is calculated as 314.01 A/cm2, and the power density is 21.98 MW/cm3. Moreover, the oxygen vacancies' defects and ferroelectric domain mechanism for enhanced breakdown strength as well as high energy density were discussed. These findings broaden the horizon for lead-free dielectrics and show promising applications for pulse power capacitors.

This study fabricated SrTiO₃ grain boundary layer ceramics using hot isostatic pressing (HIP), achieving a remarkably high dielectric constant of 60,350 and a superior breakdown strength of 1722 kV/m. Microstructural characterization via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that HIP treatment significantly refined grain size uniformity and homogenized bismuth distribution at grain boundaries, thus enhancing the interfacial barrier effect. Probe-based impedance spectroscopy elucidated the dielectric behavior and conduction mechanisms of individual grain boundaries. HIP promotes the formation of interfacial barrier layers (IBLs), significantly improving electrical performance. Compared to untreated samples (average breakdown strength: 555 kV/m), HIP-processed ceramics exhibited a threefold enhancement in breakdown strength (1722 kV/m). The treated ceramic exhibited excellent temperature stability, with TCC ≤8% over −55 to 125 °C. The optimized dielectric properties stem from HIP-induced structural modifications, including reduced oxygen vacancy concentrations and homogenized electronic distribution at grain boundaries. These findings establish a quantitative correlation between HIP parameters, grain boundary restructuring, and macroscopic performance, providing critical insights for designing high-energy-density dielectric materials.