Bi0·5K0·5TiO3-based lead-free relaxor ferroelectric with high energy storage performances via the grain size and bandgap engineering

Dielectric capacitors with high energy storage performance show a huge competitive advantage for use in vehicles and power electronics. Here, the (1-x) (0.75Bi0·5K0·5TiO3−0.25BiFeO3) – xSr0.7Bi0·2TiO3 (BKT-BF-xSBT) materials were designed based on the dual optimization strategy of grain size and bandgap. The optimal performance was obtained in the BKT-BF-0.4SBT sample, achieving high energy storage density Wrec of 5.21 J/cm3 and high energy storage efficiency η of 90.87% at 360 kV/cm. The addition of SBT optimized the microstructure and relaxation behavior of BKT-BF ceramic, giving rise to the formation of polar nanoregions (PNRs), small grain size (G), compact grain boundaries, and wide bandgap (Eg) synchronously. Encouragingly, prominent stabilities against temperature, frequency, and cycle numbers, and favorable charge/discharge performance (power density PD ≈ 64.5 MW/cm3, τ0.9 ≈ 90 ns) are also accomplished in designed BKT-based ceramics. These findings indicate that the BKT-BF-xSBT ceramic system has excellent potential in the dielectric energy storage field and also provides a viable prospect for engineering design of high-efficiency lead-free dielectrics via bandgap and grain size.