Significantly Enhanced Energy Storage Performance in High Hardness BKT-Based Ceramic via Defect Engineering and Relaxor Tuning

Hybrid electric cars and pulsed power technologies have increased the demand for capacitors with high energy density, wide temperature stability, high operating voltage, and good mechanical qualities. In this work, (1 – x) (0.6Bi0.5K0.5TiO3-0.4BiFeO3)-x(Na0.4Sm0.2NbO3) ((1 – x) (BKTBF)-xNSN) relaxor ceramics were prepared by constructing morphotropic phase boundary (MPB) combined with oxygen vacancy defect engineering. It is worth noting that the 0.6BKT-0.4BFO ceramics at MPB have a high Pmax ∼ 60 μC/cm2. The ultra-hard (HV = 10.7 GPa) BKTBFO-0.16NSN relaxor ferroelectric ceramic achieves a high Wrec of 6.52 J/cm3, a working temperature of 20–120 °C, and a working frequency of 1–1000 Hz. Additionally, the BKTBFO-0.16NSN ceramic demonstrates comprehensive pulse charge–discharge performance (Imax = 17.2 A, CD = 546.7 A/cm2, PD = 54.7 MW/cm3, and t0.9 = 59 ns) and excellent stability (25–125 °C and 104 charge–discharge cycles). This study offers a novel approach for the practical implementation of high-performance pulse capacitors, which will undoubtedly stimulate further research and development of high-Pmax energy storage dielectrics (such as BNT, BKT, and BFO).