Enhancement of energy storage and hardness of (Na0.5Bi0.5)0.7Sr0.3TiO3-based relaxor ferroelectrics via introducing Ba(Mg1/3Nb2/3)O3

High comprehensive performances with large energy storage density (Wrec), high efficiency (η), good hardness (H), and large operating temperature range are the main challenge in applications of modern electronics and electrical power systems. Herein, excellent comprehensive energy storage performances [high Wrec of 5.50 J/cm3, large η of 90.10%, and broad usage temperature range (20–200 °C)] and ultrahigh H of 7.35 GPa in lead-free (Na0.5Bi0.5)0.7Sr0.3TiO3-based (BNST) ceramics are achieved synergistically. Improving dielectric breakdown strength (Eb), mitigating early polarization saturation, large polarization difference, and decreasing grain size are beneficial to the enhancement of comprehensive performances. Further analysis of intrinsic electronic structure indicates that the introduction of Ba(Mg1/3Nb2/3)O3 (BMN) is conducive to enhancing Eb values of BNST via first-principle calculation upon density functional theory (DFT), which can also be verified by experiments. Significantly domain relaxor behavior, as evidenced by piezoresponse force microscopy (PFM) and Vogel-Fulcher (V-F) model, provides strong evidence for restraining early polarization saturation and large polarization difference. Additionally, for practical applications, the BNST-based ceramics exhibit a large power density (49.26 MW/cm3) and fast discharge time (∼120.00 ns) over broad temperature range (20–140 °C). We believe that these findings in this study can provide an effective guideline approach to attain high-performance capacitors for application in pulsed power capacitors.